HomeMy WebLinkAboutState of Hawaii, DBEDT, OPSD, CZM - Low Impact Development 2006LOW IMPACT DEVELOPMENT
A PRACTITIONER’S GUIDE
June 2006
Horsley Witten Group
HAWAII
LID
LID WORKBOOK: A PRACTITIONER’S GUIDE
A publication of the Hawaii Offi ce of Planning, Coastal Zone Management Program,
Pursuant to National Oceanic and Atmospheric Administration Award No. NA03NOS4190082.
LID WORKBOOK: A PRACTITIONER’S GUIDE
Agenda
Low Impact Development
A Practitioner’s Guide
8:00 Registration
8:30 Welcome/Introductions
8:45 Introduction to LID
Better Site Design Principles
The Value of LID vs. Conventional Design
Effectiveness
Cost Comparisons
9:30 Road Design – How Much is Enough?
Introduction to the Issue
Appropriate Design Standards
Case Studies – Precedents from Other States
10:00 Break
10:15 Stormwater Management and LID
Design Criteria for Hawaii
BMP Selection and Design
Case Studies
Operation and Maintenance Requirement
Incorporating LID into Design Codes
11: 30 Wastewater Management and LID
Hawaii Wastewater Management Requirements
Wastewater Impacts on Drinking and Coastal Waters
Alternative Wastewater Management Options
Case Studies
12:00 Overview of Available LID References
12:15 Adjourn
Laura Thielen
Mark Nelson - Maui, Kauai
Scott Horsley - Hawaii, Oahu
Michelle West - Maui, Kauai
Rich Claytor - Hawaii, Oahu
Scott Horsley - Hawaii, Oahu
Michelle West - Maui, Kauai
Rich Claytor - Hawaii, Oahu
Mark Nelson - Maui, Kauai
LID WORKBOOK: A PRACTITIONER’S GUIDE
1.0 Overview of Low Impact Development Principles
1.1 The Problem with Convential Design.......................................................1-1
1.2 Defi nition of LID .....................................................................................1-2
1.3 Goals of LID ............................................................................................1-2
1.4 Benefi ts of LID ........................................................................................1-2
1.5 LID Planning Process .............................................................................1-3
1.6 LID Categories .........................................................................................1-3
1.7 LID Best Management Practices .............................................................1-4
1.8 LID Case Studies ...................................................................................1-12
1.9 The Value of Implementing LID.............................................................1-16
1.10 References...............................................................................................1-17
2.0 Road Design Criteria
2.1 Goal – Better Road Design Criteria .........................................................2-1
2.2 Functional Classes of Roads ....................................................................2-1
2.3 Conventional Road Design ......................................................................2-2
2.4 Better Design Criteria ..............................................................................2-3
2.4.1 Right of Way (ROW) Width......................................................... 2-4
2.4.2 Pavement Width............................................................................2-4
2.4.3 Parking Requirements...................................................................2-6
2.4.4 Driveway Width and Layout.........................................................2-7
2.4.5 Curb Requirements.......................................................................2-7
2.4.6 Size of Vegetated Buffer Strips.....................................................2-8
2.4.7 Sidewalk and Bike Path Layout....................................................2-8
2.4.8 Stormwater Treatment...................................................................2-9
2.4.9 Design Speed.................................................................................2-9
2.4.10 Minimum Sight Distance.............................................................2-10
2.4.11 Maximum and Minimum Grade..................................................2-10
2.4.12 Minimum Centerline Radius....................................................... 2-10
2.4.13 Length and Radius of Cul-de-sacs.............................................. 2-10
2.4.14 Intersection Approach Speed and Sight-distance....................... 2-11
2.4.15 Minimum Intersection Curb Radii............................................. 2-12
2.4.16 Intersection Layout..................................................................... 2-12
2.5 Summary ................................................................................................2-13
2.6 Case Study...............................................................................................2-13
2.7 References .............................................................................................2-16
3.0 Stormwater Management
3.1 Introduction - Why Stormwater Matters ..................................................3-1
3.2 The Concept of Integrated Stormwater Management ..............................3.2 The Concept of Integrated Stormwater Management ..............................3.2 The Concept of Integrated Stormwater Management 3-7
Table of Contents
LID WORKBOOK: A PRACTITIONER’S GUIDE
3.3 Stormwater Criteria and Standards ...................................................... 3-10
3.3.1 Designation of Stormwater “Hotspot” Land Uses......................3-10
3.3.2 General Performance Standards .................................................3-11
3.3.3 Treatment Criteria ......................................................................3-12
3.4 Acceptable Best Management Practices (BMPs) ..................................3-14
3.4.1 Acceptable Water Quality Practice List ....................................3-15
3.4.2 Minimum Design Criteria for BMPs .........................................3-17
3.4.2.1 Stormwater Ponds/Wetlands........................................3-17
3.4.2.2 Stormwater Infi ltration.................................................3-30
3.4.2.3 Stormwater Filtering Systems......................................3-39
3.4.2.4 Open Channel Systems................................................3-50
3.5 Selecting the Most Effective Stormwater Treatment System . .3-57
3.5.1 Step 1-Land Use ........................................................................ 3-60
3.5.2 Step 2-Physical Feasibility .........................................................3-61
3.5.3 Step 3-Watershed .......................................................................3.5.3 Step 3-Watershed .......................................................................3.5.3 Step 3-Watershed 3-63
3.5.4 Step 4-Stormwater Management Capability ..............................3-64
3.5.5 Step 5-Pollutant Removal .........................................................3-65
3.5.6 Step 6-Community and Environmental .....................................3-65
3.6 General Landscaping for all BMPs ........................................................3-67
3.6.1 General Landscaping Guidance for All Stormwater BMPs........3-68
3.6.2 Other Considerations in Stormwater BMP Landscaping............3-73
3.7 Case Studies ...........................................................................................3-74
3.7.1 BMP Selection Example.............................................................3-74
3.7.2 Treatment Volume Calculation................................................... 3-76
3.8 References.............................................................................................. 3-78
4.0 Wastewater Management
4.1 Introduction – Overview of Hawaii Regulations .....................................4-1
4.2 Approved Wastewater Treatment Technologies ......................................4-2
4.2.1 Septic Systems/Wastewater Treatment Facilities ..........................4-3
4.3 Alternative Wastewater Technologies ......................................................4-6
4.4 Clustered Wastewater Systems. .............................................................4-11
4.5 Centralized Wastewater Systems ..........................................................4-12
4.6 Wastewater Reuse .................................................................................4-12
4.7 Servicing Options for Rural Communities ...........................................4-13
4.8 Opportunities to Implement Alternative Wastewater Strategies ............4-28
4.9 Case Studies ...........................................................................................4-38
4.10 Useful Weblinks .....................................................................................4-53
4.11 References...............................................................................................4-54
5.0 LID Resources
6.0 Workshop Presentation Slides
LID WORKBOOK: A PRACTITIONER’S GUIDE
LIST OF FIGURES
Figure 1.1 Example of Natural Resource Inventory Plan ..........................................................1-5
Figure 1.2 Fit the design of a site to the terrain and natural features .........................................1-6
Figure 1.3 Residential Road in Saipan that is much wider than necessary ................................1-7
Figure 1.4 Turnaround Options for Residential Streets .............................................................1-8
Figure 1.5 Examples of Permeable Pavers ................................................................................1-9
Figure 1.6 Use of a Grassed Filter Strip ....................................................................................1-9
Figure 1.7 Dry Well .................................................................................................................1-10
Figure 1.8 Rooftop Runoff is directed to a landscaped area around this house in Saipan .......1-11
Figure 1.9 Residential Subdivision - Conventional Design and Better Site Design ................1-13
Figure 1.10 Commercial Development - Conventional Design and Better Site Design ...........1-14
Figure 1.11 Single Family Residential Site Plan.........................................................................1-15
Figure 2.1 Typical Road Functional Classes............................................................................. 2-2
Figure 2.2 Typical Cross-section and Right-of-way.................................................................. 2-5
Figure 2.3 Example of Queuing Lane..................................................................................... ...2-6
Figure 2.4 Alternative to Street Parking..................................................................................... 2-6
Figure 2.5 Example Cross-section with Open Channel..............................................................2-9
Figure 2.6 Common and Alternative Turnarounds................................................................... 2-11
Figure 2.7 Sample Layout........................................................................................................ 2-12
Figure 2.8 Plan View of the Fields........................................................................................... 2-14
Figure 3.1 Water Balance at Developed and Undeveloped Sites ...............................................3-2
Figure 3.2 Relationship Between Impervious Cover and Runoff Coeffi cient ...........................3-2
Figure 3.3 Hydrographs Before and After Development ...........................................................Figure 3.3 Hydrographs Before and After Development ...........................................................Figure 3.3 Hydrographs Before and After Development 3-3
Figure 3.4 The Integrated Stormwater Management Site Design Process ................................3-8
Figure 3.5 Micropool Extended Detention Pond (P-1) ............................................................3-18
Figure 3.6 Extended Detention Shallow Wetland (P-2) ...........................................................3-19
Figure 3.7 Wet Extended Detention Pond (P-3) ......................................................................3-20
Figure 3.8 Infi ltration Trench (I-1) ...........................................................................................3-31
Figure 3.9 Sand Filter (F-1) .....................................................................................................3-40
Figure 3.10 Organic Filter (F-2) ................................................................................................3-41
Figure 3.11 Bioretention (F-3) ...................................................................................................3-42
Figure 3.12 Dry Swale (O-1) .....................................................................................................3-51
Figure 3.13 Planting Zones for Bioretention Facilities ..............................................................3-72
Figure 3.14 BMP Selection at the Honu Beach Shopping Center.............................................. 3-75
Figure 3.15 Hypothetical Medium-density Residential Development- Aloha Estates............... 3-76
Figure 4.1 Septic Systems ......................................................................................................... 4-3
Figure 4.2 The Rural Servicing Wheel......................................................................................4-13
LIST OF TABLES
Table 1.1 LID General Categories and Specifi c BMPs ............................................................1-4
Table 1.2 Comparison of Conventional Versus LID Construction Costs ..............................1-16
Table 2.1 Minimum Pavement Widths ....................................................................................2-5
Table 2.2 Turning Radius of Design Vehicles .......................................................................2-11
LID WORKBOOK: A PRACTITIONER’S GUIDE
Table 2.3 Design Criteria ......................................................................................................2-13
Table 3.1 Classifi cation of Stormwater Hotspot Land Uses ..................................................3-11
Table 3.2 Water Quality Storm Depth Based on Annual Rainfall (AR) ................................3-13
Table 3.3 List of BMPs Acceptable for Water Quality ..........................................................3-16
Table 3.4 Three Design Variants for the Island Ponds and Wetlands ....................................3-23
Table 3.5 Typical Maintenance Inspection Frequencies for Stormwater Pond/Wetlands ......3-29
Table 3.6 Water Quality Volume for Infi ltration Based on Annual Rainfall ..........................3-33
Table 3.7 Three Design Variants for Island Infi ltration Practices...........................................3-34
Table 3.8 Typical Maintenance Problems for Infi ltration Practices .......................................3-37
Table 3.9 Typical Maintenance Activities for Infi ltration Trenches ..........................................3-38
Table 3.10 Three Design Variants for Island Biorention ..........................................................3-44
Table 3.11 Construction Specifi cations for Island Bioretention Areas ...................................3-47
Table 3.12 Recommended Maintenance Activities for Bioretention Areas .............................3-49
Table 3.13 Three Design Variants for Island Swales ...............................................................3-53
Table 3.14 Conditions where Check Dams (CD) are needed to get Surface WQ Storage ......3-55
Table 3.15 Recommended Maintenance Activities for Swales ................................................3-57
Table 3.16 BMP Selection Matrix 1-Land Use ........................................................................3-61
Table 3.17 BMP Selection Matrix 2-Physical Feasibility ........................................................3-62
Table 3.18 BMP Selection Matrix 3-Watershed ......................................................................Table 3.18 BMP Selection Matrix 3-Watershed ......................................................................Table 3.18 BMP Selection Matrix 3-Watershed 3-63
Table 3.19 BMP Selection Matrix 4-Stormwater Management Capability .............................3-64
Table 3.20 BMP Selection Matrix 5-Pollutant Removal .........................................................3-65
Table 3.21 BMP Selection Matrix 6-Community and Environmental .....................................3-66
Table 3.22 Planting Soil Characteristics ..................................................................................3-70
Table 3.23 Planting Plan Design Considerations............ .........................................................3-72
Table 3.24 Planting Specifi cation Issues for Bioretention Areas..............................................3-73
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-1
1As research, technology, and information
transfer have improved over recent years,
alternative approaches are being sought by
the public and regulatory boards to reduce the
environmental impacts from new development
and redevelopment. Developers and designers
are also seeking alternatives to expedite
permitting processes, reduce construction costs,
reduce long-term operation and maintenance
costs, and increase property values. Low
Impact Development sometimes referred to as
“Low Impact Design” (LID) has emerged as an
effective way to address these issues.
LID is a relatively new comprehensive planning and engineering design approach that surfaced
in the early 90s. Since then, much has been learned about which techniques work in the fi eld and
which do not. The ultimate goal of this LID workbook is to compile this hard-won knowledge
and experience into a single comprehensive handbook that is useful to planners, engineers, and
the regulating community in order to protect the vital water resources of the Hawaiian Islands.
The purpose of this chapter is to provide an introduction to LID, as well as guidance to plan for
and implement LID practices for new development and redevelopment projects in the State of
Hawaii. While reducing the impacts from development may be achieved through both regulatory
and non-regulatory techniques, this chapter focuses on the site-level planning and design tools
available to the development community. Chapters 2 - 4 provide further detail on road design
criteria, stormwater management, and wastewater management. LID resources are included in
Chapter 5 for more information on these topics.
1.1 The Problem with Conventional Design
For the purposes of this chapter, Conventional Design can be viewed as the style of suburban
development that has evolved over the past 50 years. This development pattern, based on
conventional zoning codes, often results in sprawl with developments associated large lot areas,
loss of natural areas, and alteration of hydrologic systems. Too often, the development process
begins with the clearing and leveling of the entire parcel. The conventional developments that
follow commonly contain wide roads, monolithic parking lots, segregated land uses, enclosed
drainage systems for stormwater/wastewater conveyance, and large “hole-in-the-ground”
detention basins. The large impervious areas prevent water from infi ltrating into the ground
(which normally replenishes groundwater supplies and supports nearby wetlands and streams
with basefl ow) and quickly convey polluted runoff into nearby water bodies. Conventional
landscaping of these developments brings additional concerns including the introduction of non-
native plants, use of herbicides, pesticides and fertilizers, and excessive water consumption.
Overview of Low Impact Development Principles
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-2
1.2 Defi nition of LID
LID is defi ned as a more sustainable land development pattern than the conventional method
currently used in most areas. It incorporates a suite of landscaping and design techniques known
as “Better Site Design” that attempt to maintain the natural, pre-development hydrology of a
site and the surrounding watershed. An important LID principle is the idea that stormwater
is not merely a waste product to be disposed of, but rather that rainwater is a resource. LID
also integrates a range of structural best management practices (BMPs) for road design and
stormwater and wastewater management systems that minimize environmental impacts. These
are discussed in more detail in Chapters 2-4.
1.3 Goals of LID
The aim of LID is to reduce the environmental impact “footprint” of the site while retaining
and enhancing the owner/developer’s purpose and vision for the site. Many of the LID
concepts employ non-structural on-site treatment that can reduce the cost of infrastructure
while maintaining or even increasing the value of the property relative to conventional designed
developments. The goals of LID include:
• Prevent environmental impacts rather than having to mitigate for them;
• Manage water (quantity and quality) as close to the source as possible and minimize the use
of large or regional collection and conveyance;
• Preserve natural areas, native vegetation and reduce the impact on watershed hydrology;
• Use natural drainage pathways as a framework for site design;
• Utilize less complex, non-structural methods for stormwater/wastewater management that are
lower cost and lower maintenance than conventional structural controls; and
• Create a multifunctional landscape.
1.4 Benefi ts of LID
LID provides important benefi ts to the local municipality, the developer, and the general
public. More concentrated (cluster) design, with less impervious area and smaller infrastructure
(stormwater drainage and other utilities), means signifi cant construction cost savings to
developers. Less impervious surface creates less surface runoff, which will decrease the burden
to municipal drainage infrastructure. These techniques also reduce nonpoint source pollution
to drinking water supplies, recreational waters, and wetlands, saving future expenditures for
restoration of valuable water resources. Other LID benefi ts include:
• Reduced long-term operation and maintenance costs;
• Increased property values;
• Easier compliance with wetland and other resource protection regulations;
• More open space for recreation;
• More pedestrian friendly neighborhoods;
• Protection of sensitive forests, wetlands, and habitats; and
• More aesthetically pleasing and naturally attractive landscape.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-3
1.5 LID Planning Process
Site design should be done in unison with the design and layout of stormwater and wastewater
infrastructure in attaining management and land use goals. The LID process utilizes a three-step
process as follows:
1. Avoid the Impacts – Preserve Natural Features and use Conservation Design Techniques.
2. Reduce the Impacts – Reduce Impervious Cover.
3. Manage the Impacts – Utilize Natural Features and Natural Low-Impact techniques to
manage stormwater.
The fi rst step in the planning and design process is to avoid or minimize disturbance by
preserving natural areas or strategically locating development based on the location of resource
areas and physical conditions at a site. Resources can include drinking water supply areas,
streams/rivers, wetlands, coral reefs, sensitive habitat areas and scenic views, all of which should
be set aside and preserved. Constraints include poor soils that cannot support septic systems and
steep slopes which make construction diffi cult and expensive. The mapping of these areas results
in “building envelopes,” areas which can support development economically and ecologically.
Once sensitive resource areas and site constraints have been avoided, the next step is to minimize
the impact of land alteration by reducing impervious areas. Finally, for the areas that must be
impervious, alternative and “natural-systems” stormwater management techniques are chosen as
opposed to the more routine structural, “pipe-to-pond,” approach.
1.6 LID Categories
Stormwater LID practices and techniques covered in this chapter are grouped into the following
three categories:
Preservation of Natural Features and Conservation Design: Preservation of natural features
includes techniques to foster the identifi cation and preservation of natural areas that can
be used in the protection of water resources. Conservation Design includes laying out the
elements of a development project in such a way that the site design takes advantage of a site’s
natural features, preserves the more sensitive areas, and identifi es any site constraints and
opportunities to prevent or reduce impacts.
Reduction of Impervious Cover: Reduction of Impervious Cover includes methods to reduce
the amount of rooftops, parking lots, roadways, sidewalks and other surfaces that do not allow
rainfall to infi ltrate into the soil, in order to reduce the volume of stormwater runoff, increase
groundwater recharge, and reduce pollutant loadings generated from a site.
Utilization of Natural Features and Source Control for Stormwater Management: Utilization
of Natural Features for Stormwater Management includes design strategies that use natural
features to help manage and mitigate runoff, rather than structural stormwater controls. Source
Control for Stormwater Management includes elements to mitigate or manage stormwater in a
more natural manner.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-4
1.7 LID Best Management Practices
Table 1.1 lists the specifi c LID BMPs and techniques for each of the three categories, followed
by a description of each practice.
Table 1.1 LID General Categories and Specifi c BMPs
Preservation of Natural Features and Conservation Design
1. Preservation of Undisturbed Areas
2. Preservation of Buffers
3. Reduction of Clearing and Grading
4. Locating Sites in Less Sensitive Areas
5. Open Space Design
Reduction of Impervious Cover
6. Roadway Reduction*
7. Sidewalk Reduction*
8. Driveway Reduction
9. Cul-de-sac Reduction
10. Building Footprint Reduction
11. Parking Reduction
Utilization of Natural Features and Source Control for Stormwater Management
12. Vegetated Buffer/Filter Strips
13. Open Vegetated Channels**
14. Bioretention and Rain Gardens**
15. Infi ltration**
16. Rooftop Runoff Reduction Mitigation
17. Stream Daylighting for Redevelopment Projects
18. Tree Planting
* These practices are described in further detail in Chapter 2.**These practices are described in further detail in Chapter 3.
Practice #1 – Preservation of Undisturbed Areas: Important natural features and areas such as
undisturbed forested and native vegetated areas, natural terrain, riparian corridors, wetlands and
other important site features should be delineated and placed into permanent conservation areas.
• Delineate and defi ne natural conservation areas before performing site layout and design; and
• Ensure that conservation areas and native vegetation are protected in an undisturbed state
through the design, construction and occupancy stages.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-5
Practice #2 – Preservation of Buffers: Naturally vegetated buffers should be defi ned,
delineated and preserved along perennial streams, rivers, coastlines, and wetlands.
• Delineate and preserve naturally vegetated riparian buffers (defi ne the width, identify the
target vegetation, designate methods to preserve the buffer indefi nitely);
• Ensure that buffers and native vegetation are protected throughout planning, design,
construction and occupancy; and
• Consult local planning authority for minimum buffer width and/or recommended width.
Practice #3 – Reduction of Clearing and GradingPractice #3 – Reduction of Clearing and Grading: Clearing and Grading of the site should
be limited to the minimum amount needed for the development function, road access, and
infrastructure (e.g. utilities, wastewater disposal, stormwater management). Site foot-printing
should be used to disturb the smallest possible land area on a site.
• Restrict clearing to the minimum area required for building footprints, construction access,
and safety setbacks;
• Establish limits of disturbance for all development activities;
• Use site foot-printing to minimize clearing and land disturbance;
• Limit site mass grading approach; and
• Use alternative site designs that use open-space or “cluster” developments.
Figure 1.1 Example of Natural Resource Inventory Plan.
(Source: Georgia Stormwater Manual, 2001)
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-6
Practice #4 – Locating Sites in Less Sensitive AreasPractice #4 – Locating Sites in Less Sensitive Areas: Development sites should be located to
avoid sensitive resource areas such as fl oodplains, steep slopes, erodible soils, wetlands, mature
forests and critical habitat areas. Buildings, roadways, and parking areas should be located to fi t
the terrain and in areas that will create the least impact.
• Ensure all development activities do not encroach on designated fl oodplain and/or wetland
areas;
• Avoid development on steep slope
areas and minimize grading and
fl attening of hills and ridges;
• Leave areas of porous or highly
erodible soils as undisturbed
conservation areas;
• Develop roadway patterns to
fi t the site terrain and locate
buildings and impervious
surfaces away from steep slopes,
drainageways and fl oodplains; and
• Locate site in areas that are less
sensitive to disturbance or have a
lower value in terms of hydrologic
function.
Practice #5 – Open Space DesignPractice #5 – Open Space Design:
Open space site designs (also referred
to as conservation development or
clustering) incorporate smaller lot
sizes to reduce Figure 1.2 Fit the
design of a site to the terrain and
natural features
overall impervious cover while
providing more undisturbed open
space and protection of water
resources.
• Use a site design which
concentrates development and
preserves open space and natural
areas of the site;
• Locate the developed portion of the
cluster areas in the least sensitive areas of the site (see practice #4); and
• Utilize reduced setbacks and frontages, and narrower right-of-way widths to design non-
traditional lot layouts within the cluster.
Figure 1.2 Fit the design of a site to the terrain and
natural features.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-7
Practice #6 – Roadway ReductionPractice #6 – Roadway Reduction: Roadway lengths and widths should be minimized on a
development site where possible to reduce overall imperviousness (See Chapter 2 for more
detailed information on this practice).
• Consider different site and road layouts that reduce overall street length;
• Minimize street width by using narrower street designs that are a function of land use,
density and traffi c demand; and
• Use smaller side yard setbacks to reduce total road length.
Practice #7 – Sidewalk Reduction: Sidewalk lengths should be minimized on a development
site where possible to reduce overall imperviousness (Chapter 2 includes more information on
this practice).
• Locate sidewalks on only one side of residential streets;
• Provide common walkways linking pedestrian areas;
• Use alternative sidewalk and walkway surfaces; and
• Shorten front setbacks to reduce walkway lengths
Practice #8 – Driveway ReductionPractice #8 – Driveway Reduction: Driveway lengths and widths should be minimized on a
development site where possible to reduce overall imperviousness.
• Use shared driveways that connect two or more homes together;
• Use alternative driveway surfaces such as permeable pavers (see Figure 1.5); and
• Use smaller lot front building setbacks to reduce total driveway length.
Figure 1.3 Residential road that is much wider than necessary to accommodate residential traffi c fl ow.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-8
Practice #9 – Cul-de-sac Reduction: Minimize the number of cul-de-sacs and incorporate
landscaped areas to reduce their impervious cover. The radius of a cul-de-sac should be
the minimum required to accommodate emergency and maintenance vehicles. Alternative
turnarounds should also be considered.
• Reduce the radius of the turnaround bulb or consider alternative cul-de-sac design, such as
“tee” turn-a-rounds or looping lanes;
• Apply site design strategies that minimize dead-end streets; and
• Create a pervious island or a stormwater bioretention area in the middle of the cul-de-sac to
reduce impervious area.
Figure 1.4 Turnaround Options for Residential Streets.
(Source: Adapted from Schueler, 1995)
Practice #10 – Building Footprint ReductionPractice #10 – Building Footprint Reduction: The impervious footprint of residences and
commercial buildings can be reduced by using alternate or taller buildings while maintaining the
same fl oor to area ratio.
• Use alternate or taller building designs to reduce the impervious footprint of buildings;
• Consolidate functions and buildings or segment facilities to reduce footprints of structures;
and
• Reduce directly connected impervious areas.
Practice #11 – Parking ReductionPractice #11 – Parking Reduction: Reduce the overall imperviousness associated with parking
lots by eliminating unneeded spaces, providing some compact car spaces, minimizing stall
dimensions, incorporating effi cient parking lanes, utilizing multi-storied parking decks, and using
porous paver surfaces or porous concrete in overfl ow parking areas where feasible.
• Reduce the number of unneeded parking spaces by examining minimum parking ratio
requirements, and set a maximum number of spaces;
• Reduce the number of unneeded parking spaces by examining the site’s accessibility to mass
transit;
• Minimize individual parking stall dimensions;
• Examine the traffi c fl ow of the parking lot design to eliminate unneeded lanes / drive aisles;
• Consider parking structures and shared parking arrangements between non-competing uses;
• Use alternative porous surface for overfl ow areas, or in main parking areas if not a high
traffi c parking lot;
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-9
• Use landscaping or vegetated stormwater practices in parking lot islands; and
• Provide incentives for compact cars.
Practice #12 – Vegetated Buffer/Filter StripsPractice #12 – Vegetated Buffer/Filter Strips: Undisturbed natural areas such as forested
conservation areas and stream buffers, or vegetated fi lter strips, can be used to treat and control
stormwater runoff from some areas of a development project. (Figure 1.6)
• Direct runoff towards buffers and
undisturbed areas using sheet fl ow or
a level spreader to ensure sheet fl ow;
• Utilize natural depressions for runoff
storage;
• Direct runoff and nature of runoff
(sheet fl ow vs. shallow concentrated
fl ow) to buffer/fi lter strip areas;
• Examine the slope, soils and
vegetative cover of the buffer/fi lter
strip; and
• Disconnect impervious areas to these
areas.
Figure 1.6 Use of a Grassed Filter Strip.
Figure 1.5 Examples of Permeable Pavers.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-10
Practice #13 – Open Vegetated ChannelsPractice #13 – Open Vegetated Channels: The natural drainage paths of a site, or properly
designed and constructed vegetated channels, can be used instead of constructing underground
storm sewers or concrete open channels. Where density, topography, soils, slope, and safety
issues permit, vegetated open channels can be used in the street right-of-way to convey and treat
stormwater runoff from roadways.
• Preserve natural fl ow paths in the site design;
• Direct runoff to natural drainage ways, ensuring that peak fl ows and velocities will not cause
channel erosion;
• Use vegetated open channels (enhanced wet or dry swales or grass channels) in place of curb
and gutter, and pipes, to convey and treat stormwater runoff; and
• Ensure runoff volumes and velocities provide adequate residence times and non-erosive
conditions (i.e. use of check dams).
Practice #14 – Bioretention and Rain Gardens: Provide stormwater treatment for runoff from
impervious surfaces using bioretention areas or rain gardens that can be integrated into required
landscaping areas and traffi c islands.
• Integrate bioretention into a parking lot or roadway design;
• Integrate bioretention, or rain gardens, into on-lot residential designs;
• Closely examine runoff volumes and velocities to ensure runoff enters bioretention in a
distributed manner and in a non-erosive condition;
• Ensure the bioretention has proper pre-treatment;
• Carefully select the landscaping materials required; and
• Works well as a retrofi t or in redevelopment projects.
Practice #15 – Infi ltration: Utilize infi ltration trenches,
basins, or leaching chambers to provide groundwater
recharge, mimic existing hydrologic conditions, and reduce
runoff and pollutant export. Permeable paving surfaces may
also be used where site conditions are appropriate.
• May be used for roadway or parking impervious areas if
adequate pre-treatment is provided;
• Rooftop runoff may discharge directly to drywells or
infi ltration chambers (Figure 1.7);
• The site must have soils with moderate to high
infi ltration capacities and must have adequate depth to
groundwater;
• Certain sites (i.e. pollutant hotspots) require additional
pretreatment prior to infi ltration;
• Use porous pavers only in low traffi c areas or for
pedestrian walkways/plazas; and
• Poor soils may preclude aggressive infi ltration.
Figure 1.7 Dry Well.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-11
Practice #16 – Rooftop Runoff Reduction Practice #16 – Rooftop Runoff Reduction
MitigationMitigation: Direct runoff from residential
rooftop areas to pervious areas, lower-impact
practices, or utilize “green roof” strategies to
reduce rooftop runoff volumes and rates.
• Direct rooftop runoff to pervious areas
such as yards, open channels, or vegetated
areas;
• Direct rooftop runoff to lower-impact
practices such as rain barrels, cisterns,
drywells, rain gardens, or stormwater
planters; and
• Utilize “green roofs” (specially designed
vegetated rooftops) to reduce stormwater
runoff from rooftops.
Practice #17 – Stream Daylighting for Redevelopment ProjectsPractice #17 – Stream Daylighting for Redevelopment Projects: Daylight previously-
culverted/piped streams to restore natural habitats, better attenuate runoff, and help reduce
pollutant loads where feasible and practical.
• Daylighting should be considered when a culvert replacement is scheduled;
• Restore historic drainage patterns by removing closed drainage systems and constructing
stabilized, vegetated streams;
• Carefully examine fl ooding potential, utility impacts and/or prior contaminated sites; and
• Consider runoff pretreatment and erosion potential of restored streams/rivers.
Practice #18 – Tree PlantingPractice #18 – Tree Planting: Plant or conserve trees at new or redevelopment sites to reduce
stormwater runoff, increase nutrient uptake, provide bank stabilization, provide shading, and
provide wildlife habitat. Trees can be used for applications such as landscaping, stormwater
management practice areas, conservation areas and erosion and sediment control.
• Conserve existing trees during construction by performing an inventory of the existing forest
and identifying trees to protect;
• Design the development with tree conservation in mind, protect trees during construction,
and protect trees after construction;
• Plant trees at development sites by fi rst selecting the planting sites and then evaluate and
improve the planting sites. Trees should be planted in stormwater management practices and
other open spaces; and
• Tree types and locations should be chosen to withstand the constraints of the new land use
and setting.
Figure 1.8 Rooftop runoff is directed to a landscaped area around this house.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-12
1.8 LID Case Studies
The following case studies illustrate how LID practices can be successfully incorporated into site
planning. Comparisons to a conventional design approach illustrate how LID practices can be
used to reduce impacts. In addition, a single-family home example is included to show how LID
practices can also be utilized on a small (< 1 acre) scale.
Medium Density Residential Subdivision Case Study
A conventional residential subdivision design on a parcel is shown in Figure 1.9a. The entire
parcel except for the subdivision amenity area (clubhouse and tennis courts) is used for lots. The
entire site is cleared and mass graded, and no attempt is made to fi t the road layout to the existing
topography. Because of the clearing and grading, all of the existing tree cover and vegetation
and topsoil are removed, dramatically altering both the natural hydrology and drainage of the
site. The wide residential streets create unnecessary impervious cover and a curb-and-gutter
system that carries stormwater fl ows to the storm sewer system. No provision for non-structural
stormwater treatment is provided on the subdivision site.
A residential subdivision employing stormwater better site design practices is presented in
Figure 1.9b. This subdivision confi guration shows six (6) more lots than the conventional,
while also preserving a quarter of the property as undisturbed open space and vegetation.
The road layout is designed to fi t the topography of the parcel, following the high points and
ridgelines. The natural drainage patterns of the site are preserved and are utilized to provide
natural stormwater treatment and conveyance. Narrower streets reduce impervious cover
and open vegetated channels provide for treatment and conveyance of roadway and driveway
runoff. Bioretention islands at the ends of cul-de-sacs also reduce impervious cover and provide
stormwater treatment functions. When constructing and building homes, only the building
envelopes of the individual lots are cleared and graded, further preserving the natural hydrology
of the site.
Commercial Development Case Study
Figure 1.10a shows a conventional commercial development containing a supermarket,
drugstore, smaller shops and a restaurant on an adjacent lot. The majority of the parcel is a
concentrated parking lot area. The only pervious area is a small replanted vegetation area acting
as a buffer between the shopping center and adjacent land uses. Stormwater quality and quantity
control are provided by a wet extended detention pond in the corner of the parcel.
A better site design commercial development can be seen in Figure 1.10b. Here the same
amount of retail space is dispersed on the property, providing more of an “urban-village” feel
with pedestrian access between the buildings. The same number of parking spaces are broken
up into separate areas, and bioretention areas for stormwater treatment are built into parking
lot islands. A large bioretention area which serves as open green space is located at the main
entrance to the shopping center. A larger undisturbed buffer has been preserved on the site.
Because the bioretention areas and buffer provide water quality treatment, only a dry extended
detention basin is needed for water quantity control.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-13
Figure 1.9b Residential Subdivision - Better Site Design.
(Source: Georgia Stormwater Manual, 2001)
*Number of lots actually increased in Better Site Design layout.
Figure 1.9a Residential Subdivision - Conventional Design.
(Source: Georgia Stormwater Manual, 2001)
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-14
Figure 1.10b Commercial Development - Better Site Design.
(Source: Georgia Stormwater Manual, 2001)
Figure 1.10a Commercial Development - Conventional Design.
(Source: Georgia Stormwater Manual, 2001)
*Number of parking lots and amount of retail space are same in both designs.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-15
Single-family Home Case Study
This case study represents a single-family residential site. This example (see Figure 1.11)
focuses on a hypothetical site consisting of a ¼-acre lot. There are many structural and non-
structural ways that a single-family home can incorporate LID practices. Some BMPs that could
be utilized for this site are shown in Figure 1.11 and described below.
The impacts from this site can be reduced by using a cistern for rooftop runoff that overfl ows to
a drywell. In general, the primary function of cisterns is to capture and store rooftop runoff that
can be used at a later time. The drywell is intended to accept overfl ow from the cistern in larger
rain events, or when the cistern is already full from a previous storm event. Both the cistern and
the drywell help to reduce peak fl ows leaving the site.
In addition, a rain garden is used here to treat runoff from the yard and paved areas, although
rain gardens can also be designed to capture rooftop runoff. Permeable pavers can be used in the
driveway and walkway areas, and a dry swale can be used along the road to collect the overfl ow
from the rain garden, driveway, and walkways, and can help meet water quality requirements for
the site.
Figure 1.11 Single-family Residential Site Plan.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-16
1.9 The Value of Implementing LID
This introductory chapter highlights the environmental benefi ts of the LID approach. However, as
discussed briefl y in Section 1.4, there are also signifi cant cost benefi ts to developers and communities
when they follow the LID guidelines in this book. These benefi ts are seen in four areas:
• The initial construction cost for a project;
• Operation and maintenance costs for some LID-based best management practices
• Increased property values for LID sites, and;
• Future costs for clean-up or remediation of damaged watersheds or water bodies.
Cost savings are provided by using both better site design techniques and LID-based best management
practices. A case study at the end of Chapter 2 highlights the cost savings provided by an LID project
in Virginia. A 48% savings was provided by using a clustered site design and substituting open channel
stormwater management systems for underground, fi xed drainage systems.
Cost savings are found both in residential and commercial designs (Center for Watershed Protection,
1998). Four case studies developed by the Center for Watershed Protection showed savings of 5-20%
when LID approaches were compared to standard designs for the same sites (Table 1.2).
Table 1.2 Comparison of Conventional Versus LID Construction Costs
Med. Density
Residential
Low Density
Residential
Shopping Center Offi ce Park
Conv. Design $1,539,000 $143,000 $782,000 $948,000
LID Design $1,239,000 $126,000 $746,000 $788,000
Cost Savings $300,000 $17,000 $36,000 $160,000
Percent Savings 20%12%5%17%
The greatest cost savings were realized for the medium density residential development where there are
the greatest opportunities for clustering the homes and therefore reducing infrastructure costs. It is safe
to assume that similar savings can be achieved for projects in Hawaii, although the relative costs will be
different given the locations of the case study sites and the time since the analysis was conducted.
Operation and maintenance costs for the BMPs described in Chapter 3 are similar, and sometimes
less than those for standard drainage systems. In commercial settings, where parking lot islands are
used for stormwater management, the overall site maintenance costs are likely to be less for an LID-
based project. The landscaped islands must be maintained whether or not they are used for stormwater
management. The extent of landscape maintenance is not too different for each approach, and if the
islands are used for stormwater controls, there is no need to maintain other stormwater structures on the
site as well.
Evidence has also shown that the values of properties built with an LID approach equal or exceed those
developed based on a conventional design. Clustered homes adjacent to protected open space increased
in value faster than homes in a standard subdivision in Amherst, Massachusetts (Lacy, 1991). Research
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-17
in Illinois, Maryland and Virginia has found that home prices in dense residential areas are higher for
homes adjacent to stormwater BMPs such as wet ponds or other aesthetic surface water features (Adams
et al, 1986, Emmerling-DiNovo, 1995).
Finally, and perhaps most importantly, the use of an LID approach provides signifi cant environmental
benefi ts that can translate directly to cost savings in the need for future remediation of environmental
resources. LID approaches can reduce the loading of sediments nutrients and pathogens to coastal
waters and associated coral reefs in Hawaii. This improves the health of these systems and makes them
more attractive for those interested in boating, snorkeling or diving. Future development using standard
approaches will continue to threaten these systems, ultimately requiring expensive and diffi cult fi xes
if the heath of the coastal ecosystem is to be restored. If Hawaii hopes to preserve these resources for
residents and visitors, the use LID techniques provides one cost effective tool to accomplish this goal.
1.10 References
Adams, L.W., Franklin, T.M., Dove, L.E., and J.M. Duffi eld. 1986. Design Considerations for Wildlife
in Urban Stormwater Management. In Proceedings of Fifty-First North American Wildlife and
Natural Resources Conference, J.E. Townsend and R.J. Smith (eds) pp. 249-259
Arendt, Randall. 1994. Designing Open Space Subdivisions: A Practical Step-by-Step Approach. Natural
Lands Trust, Inc. Media, PA. Available from www.natlands.org or www.greenerprospects.com
Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open
Space Networks. American Planning Association. Chicago, IL. Available from the American
Planning Association at www.planning.org
Atlanta Regional Commission. August 2001. Georgia Stormwater Management Manual. Atlanta, GA.
Available from www.georgiastormwater.com
Cappiella, K., T. Schueler, T. Wright. 2004. Urban Watershed Forestry Manual. Available from www.
cwp.org
Center for Watershed Protection. 2000. “An Introduction to Better Site Design.” Watershed Protection
Techniques. Vol. 3.
Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development
Rules in Your Community. Available from www.cwp.org
Center for Watershed Protection (CWP). 1998b. Nutrient Loading from Conventional and Innovative
Site Development. Center for Watershed Protection.
Emmerling-Dinovo, C. 1995. Stormwater Detention Basins and Residential Locational Decisions.
Water Resources Bulletin 31(3):515-521.
LID WORKBOOK: A PRACTITIONER’S GUIDE 1-18
Fukuda, K., P. Lui, W. Okazaki, K. Pacheco, and N. Sultana. 2004. Impervious Cover Analysis and
Study of Existing Regulation vis-à-vis Low Impact Design for the State of Hawai’i, Prepared for
Hawai’i Offi ce of Planning, Honolulu, Hawai’i. Department of Urban and Regional Planning,
University of Hawai’i, Honolulu.
Lacy, J. 1991. Clustered Home Values Found to Appreciate More. Land Development 3(3).
Low Impact Development (LID) Center website: http://www.lowimpactdevelopment.org/
Massachusetts Executive Offi ce of Environmental Affairs (EOEA). 2005. Smart Growth Toolkit.
Boston, MA. Available from http://www.mass.gov/envir/
Metropolitan Area Planning Council (MAPC). 2005. Massachusetts Low Impact Development Toolkit
Fact Sheets. Metropolitan Area Planning Council. Boston, MA. Available from www.mapc.org/lid
MPCA. 1989. Best Management Practices for Minnesota. Minnesota Pollution Control Agency.
Minneapolis, MN.
Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated
Design Approach. Prince George’s County, Maryland, Department of Environmental Resources,
Largo, Maryland. Available from www.epa.gov
Rhode Island Department of Environmental Management. January 2005. The Urban Environmental
Design Manual. Rhode Island Department of Environmental Management, Providence, Rhode
Island. Available from http://www.dem.state.ri.us/programs/bpoladm/suswshed/pubs.htm
Schueler, T. 1995. Site Planning for Urban Stream Protection. Prepared for: Metropolitan Washington
Council of Governments. Washington, DC. Center for Watershed Protection, Ellicott City, MD.
Available from www.cwp.org
www.epa.gov/ebtpages/envismartgrowth.html Environmental Protection Agency (EPA) site on smart
growth including a focus on community based approaches to reducing sprawl.
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-1
22.1 Goal – Better Roadway Design Criteria
Roadways developed under the principals of Low Impact
Design (LID) should satisfy standard design criteria,
including safety, access and constructability, while
maximizing the livability of pedestrians, neighborhoods
and communities, and minimizing negative impacts from
stormwater runoff and pollution.
The primary goals of conventional road design are efficiency
and safety. Both are vitally important, but there is a growing
consensus that other factors have been left out. These
include the effects of roads on human and environmental
concerns, and are especially significant at the local
level. Recent publications from organizations such as the
Institute of Transportation Engineers (ITE), the American Association of State and Highway
Transportation Officials (AASHTO), and others are attempting to set better standards for local
road design.
This chapter gives an overview of the evolution of conventional road design and its problems.
Better roadway design criteria are developed based on recommendations by AASHTO, ITE
and others; new ideas are presented where applicable, and comparisons are made to typical
design standards for Hawaii where possible. Finally, a case study is presented illustrating a
development that has successfully implemented some of these criteria.
2.2 Functional Classes of Roads
Road systems are typically grouped into three functional classes, arterial, collector and local.
Arterial roads, such as interstate highways, convey traffic on a regional scale and are grade-
separated from all other roads, with access points spaced at regular intervals. These roads make
up about 12 percent of the total mileage in the United States (AASHTO, 2004). Most of these
roads are part of the National Highway System, and the standards for their design are set by
the Federal Highway Administration (FHA). These standards are based on guidelines for the
geometric design of highways developed by AASHTO and others, beginning in the early part of
the 20th Century.
Collector roads convey traffic on an intra-county or municipal scale and provide access to the
arterial roads. In urban areas, major collector roads may receive in excess of 3,500 average daily
trips (ADT), while minor collector roads typically receive 1,500 to 3,500 ADT (ITE, 1997).
These roads make up about 23 percent of the total roadway mileage in the United States. Most
of these roads are part of the state highway system; design standards for these roads are set by
the state departments of transportation.
Road Design Criteria
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-2
Local roads convey traffic on the
residential level and provide access to
collector roads, receiving an average
of 100 to 1,500 ADT. These roads
make up about 70 percent of the
total roadway mileage in the United
States. Design standards for these
roads are set at the local or municipal
level. Often, these standards were
based on the same guidelines used
to build state or federal highways, or
on early attempts to design roads for
the large scale subdivisions that were
built starting in the 1950s. Although
these standards can be appropriate
for some uses, many of the roads
that have been built based on them
are over-designed. The remainder of
this chapter will focus on local road
design.
2.3 Conventional Road Design
Conventional design of local roads has typically focused on the efficient movement of
vehicles and vehicular safety, to the detriment of other functions such as pedestrian activities,
environmental concerns, cost and community aesthetics.
For example, a local urban road in Maui County must be 28 feet wide. This road provides one
8-foot parking lane and two 10-foot travel lanes. It is an appropriate design choice for larger
streets with high traffic flows, and where ample on-street parking is required. This road can
easily serve dense developments of 6.0 or more units per acre.
In areas of low density, 2.0 units or less per acre, or even medium density, 2.1 to 6.0 units per
acre, this road may be too large. These areas do not require as much on-street parking as the
denser development. Even in the dense areas, a 28-foot road is too large in some cases. Shorter
roads, such as lanes or courts, which serve only a few houses and receive less than 250 ADT can
be designed to be narrower based on the low traffic flows and vehicle speeds.
The long, wide stretches of pavement built as a result of an over-designed road create a number
of problems:
• Vehicle speeds increase, posing a safety risk to both drivers and pedestrians. This has
a negative effect on community character, and makes it difficult for law enforcement
officers to perform proper policing.
Figure 2.1 Typical road functional classes.
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-3
• Capital expenditures for construction and maintenance are unnecessarily high.
• Larger right-of-ways (ROW) required increase clearing and reduce the amount of land
available for residential and agricultural use.
• Larger impervious areas increase stormwater runoff and reduce groundwater infiltration.
Pollutant loads are also larger, especially where curb-and-gutter systems are built.
2.4 Better Design Criteria
There is a growing consensus that better design criteria need to be developed for local roads. In
1974, the American Society of Civil Engineers (ASCE), Urban Land Institute (ULI) and National
Homebuilders Association (NHBA) published Residential Streets, an early attempt to develop
local road designs that were not based on highway standards. A subsequent edition published in
1993, and others such as Guidelines for Residential Street Design (ITE, 1997) and Guidelines for
Design of Very Low-Volume Local Roads (AASHTO, 2001) further develop the design of roads
tailored to the local setting.
Building shorter, narrower roads can have a number of benefits:
• Encourages moderate speeds through residential neighborhoods;
• Saves capital and resources;
• Creates neighborhoods that are more pedestrian friendly;
• Preserves valuable open space and agricultural land, and;
• Minimizes impervious area and its negative stormwater impacts.
The authority, and responsibility, for creating and implementing better design standards for local
roads is at the town, municipal and county level. The guidelines developed by AASHTO, ITE
and others are good starting points, but are designed to be recommendations rather than rules.
The following elements of design criteria for roads are considered in this chapter:
• Right of Way (ROW) width
• Pavement width
• Parking requirements
• Driveway width and layout
• Curb requirements
• Size of vegetated buffer strips
• Sidewalk and bike path layout
• Stormwater treatment
• Design speed
• Minimum sight distance
• Maximum and minimum grade
• Minimum centerline radius
• Length and radius of cul-de-sacs
• Intersection approach speed and sight-distance
• Minimum intersection curb radii
• Intersection layout
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-4
Other design criteria, such as vertical curve sizes, street lighting, and intersection alignments
are not discussed in this text but are given consideration in ITE’s Guidelines for Residential
Subdivision Street Design.
2.4.1 Right of Way (ROW) Width
The ROW must be wide enough to enclose all of the cross-sectional features of the roadway,
including the pavement width, curbing, buffers, sidewalks, stormwater treatment and grading.
Maui County recommends a 44-foot ROW width for 28-foot wide minor urban streets, and
a 40-foot ROW for 22-foot wide minor rural streets. ITE guidelines are more conservative,
recommending a minimum ROW width of 50 feet for low-density development and 60 feet for
medium and high-density developments. 60 feet is a common design choice throughout the
country, but can be excessive in many situations.
Wide ROWs reduce the amount of land that may be developed and increase the amount of
clearing and grading that must occur, creating negative environmental and economic effects. The
ROW need only be wide enough to contain all of the cross-sectional elements. The Maui County
guidelines are a good choice given the size of the road; further reductions might be possible if
the road width was decreased. For an 18-foot paved lane with 5-foot sidewalks offset six feet
from the road and one foot from the edge of the property lines, the ROW may be as narrow as 42
feet. Similar reductions can be made for higher-order streets. ROW widths of 24 to 52 feet are
practical for most applications.
A common justification for 60-foot ROW widths is that the additional space is required for future
roadway expansion. However, the traffic volume of most residential streets is constant over time
since additional units are unlikely to be constructed.
2.4.2 Pavement Width
The road should be wide enough to accommodate travel lanes, street parking (if required), and
the passage of emergency vehicles and the occasional delivery truck. Maui County guidelines
specify that minor urban roads be 28 feet wide and minor rural roads be 22 feet wide. These
guidelines are appropriate for high-density development or high vehicle volumes, but may be
excessive for smaller uses. AASHTO recommends that a two-lane rural road traveled at 25
mph should be 18 feet wide, while an urban road should be 20 to 28 feet wide for low-density
developments and 28 to 34 feet wide for medium density developments, depending on street
parking requirements (AASHTO, 2001; ITE, 1997). See Table 2.1 for a summary of typical
pavement width requirements.
Minimizing the pavement width has several advantages. First, the developer will save money
on labor and materials. Second, the ROW width (and clearing) will be reduced, and stormwater
impacts will be minimized. Finally, narrower roads reduce vehicle speeds, enhancing safety and
increasing the quality of life for nearby residences.
One way to reduce the width is to use a queuing lane (see Figure 2.3). Where traffic flow
is low, two-way traffic can use a single lane, and passing vehicles can queue in the parking
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-5
lane as necessary. AASHTO
recommends that a single travel
lane be 9 to 12 feet wide, and
that parking lanes be 8 to 12
feet wide (AASHTO, 2004).
Parking widths of 6 to 7 feet may
be appropriate at low speeds.
AASHTO recommends that the
use of a queuing lane be limited
to those streets receiving 50 or
less ADT (AASHTO, 2001).
However, queuing lanes can be effective for most local streets and even the smallest collector
streets, (often termed ‘sub-collector’ streets), provided that traffic flows do not require the
establishment of two clear lanes of travel. Residential Streets recommends that streets smaller
than major collector streets, which have two lanes for both parking and travel and are usually 36
feet wide, can be 26 feet wide or less using a queuing lane (ASCE, 1990).
Another option is to reduce or eliminate the need for on-street parking (for more on this topic,
see the next section).
Sufficient width must be provided for the use of emergency vehicles. The most cited vehicle
is a ladder truck used for fighting fires. This vehicle can navigate the typical 9- to 10-foot
lane outlined above, but needs extra space for setting up its outriggers when raising the ladder.
The National Fire Protection Administration recommends that a 20-foot unobstructed way be
provided; some states such as Massachusetts and Virginia require an 18-foot width. Where street
parking does not occur and the shoulder is constructed of a firm, stable material, the ladder truck
can set up one of its supports on the shoulder.
Roads can be designed that minimize impervious area while taking the requirements of
emergency vehicles into account.
Figure 2.2 Typical cross-section and right-of-way.
Table 2.1
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-6
2.4.3 Parking Requirements
Parking requirements make up a significant portion of the impervious area in a development.
Provision of street parking increases the roadway width, while off-street parking in the form of
driveways and garages increases the total amount of impervious area per lot.
Off-street parking in residential districts is
usually sized to accommodate the needs of
the resident, while on-street parking is used
for overflow requirements from visitors and
other vehicles. ITE recommends that 1.5
to 3.0 spaces be provided per dwelling unit,
depending on the size and type (ITE, 1997).
Most communities require that 2 to 2.5 spaces
be provided per single family home (CWP,
1998). Usually, a two-car garage and/or
driveway is sufficient for these needs.
A typical on-street parking space is 20 feet
long by 7 feet wide (CWP, 1998). Often,
a continuous parking lane is provided on
one or both sides of the street, depending
on the density of the development. In rural
or low-density developments, on-street
parking may be accommodated on the grassy
shoulder, provided that it has been sufficiently
compacted and stabilized. The road may
also be narrowed and widened to encourage
parking in some areas and minimize impervious
cover in others. Occasionally, lot configurations
create driveways that are long enough to
accommodate all reasonable overflow requirements,
and no on-street parking is required.
Figure 2.3 Example of queuing lane.
Figure 2.4 Alternative to street parking.
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-7
2.4.4 Driveway Width and Layout
Driveways must be wide enough to allow for the passage of vehicles, and long enough to satisfy
parking requirements. Typically, a 10-foot wide drive is sufficient for one vehicle, while 20-foot
wide drives are used for two car garages connected directly to the street (ITE, 1997). Driveways
should always be designed with proper slopes, sight distances and radii.
One way to reduce the total amount
of impervious area required by
driveways in a development is to
use shared driveways. These are
privately owned and maintained
roads, typically 16 feet wide. Maui
County recommends that these
roads serve no more than three
residences, but two to six residences
can be comfortably accessed.
Careful design can provide
sufficient space for overflow
parking while reducing the overall
area required. Since municipal
authorities do not have oversight,
it is important that the developer or
a homeowners’ association provide
for the continued maintenance.
2.4.5 Curb Requirements
Curbs establish a clear boundary between the
edge of the road and the buffer area, guarding
against erosion and protecting the roadway
edge. Curbing also protects pedestrians, and
is an integral part of a closed drainage system,
helping to deliver storm runoff to collection
basins. Vertical curbing is most commonly used
in urban areas, and is recommended by ITE
for all medium to high-density developments
(ITE, 1997). Rolled curbing, or asphalt berm,
is less expensive and is typically used in
medium to low-density developments. While
vertical curbing provides greater protection for
pedestrians, rolled curbing allows for on-street
parking using part of the shoulder, and facilitates
driveway construction.
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-8
One disadvantage to curbing is its cost; it is much more expensive to build a road with curbs
and a closed drainage systems than with grassy shoulders and open swales. Curbs also prevent
stormwater runoff from infiltrating along the side of the road, and create concentrations of debris,
pollutants and bacteria. As a result, more runoff occurs at higher pollutant concentrations on
curbed streets. Where practical, curbing should be eliminated and open drainage swales should
be used in lieu of closed drainage systems, as outlined in brief in Section 2.5.8 and in detail in
Chapter 3. In Rural By Design, Randal Arendt recommends that curb and gutter systems only
be used where high densities prohibit the use of swales (four or more units per acre), or where
erosion is a concern due to steep slopes of eight percent or more (Arendt, 1994).
One common argument against eliminating curbs is that it may increase the potential for surface
erosion or failure of the road surface at the pavement edge. However, these effects can be
mitigated by hardening the pavement grass interface through the use of grass pavers, or a low-
rising concrete strip (CWP, 1998). The use of such a strip also increases the visibility of the
roadway edge, enhancing traffic safety at night.
2.4.6 Size of Vegetated Buffer Strips
Vegetated buffer strips between the roadway edge and sidewalks or stormwater treatment
facilities offer a number of advantages. Pedestrians are given increased protection, and space
is available for such curb-side activities as garbage pickup. These areas also offer space for
landscaping improvements, which offer aesthetic advantages and reduce vehicular speeds by as
much as 10-15 mph (Burden, 1999).
ITE recommends that buffers 5 to 6 feet wide be constructed on both sides of the street; this is
also a common requirement of many municipalities. In Residential Streets, a three to five-foot
width is recommended. Using a narrower buffer strip reduces its effectiveness, but affords a
narrower ROW width and reduces clearing and grading requirements.
2.4.7 Sidewalk and Bike Path Layout
Sidewalks can enhance community character
by providing a safe place for people to walk
and play. However, sidewalks are costly
and increase the total impervious area of a
development. Many communities require
a 5-foot sidewalk on each side of the street;
ITE recommends 4-6 foot sidewalks offset 1
foot from the edge of the ROW on both sides
of the street, for medium- and high-density
developments (ITE, 1997). Typically, the
width requirement for a sidewalk is increased
if it is constructed adjacent to the edge of
the roadway, buildings, or shrubs (Burden,
1999).
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Constructing 5-foot sidewalks on both sides of the street is not always appropriate, even in
medium- to high-density developments. In Better Site Design, a 3-4 foot sidewalk on one side
of the street is proposed for most situations. A reduction in property values and safety are two
often-cited arguments against reducing sidewalk requirements. However, CWP found no marked
reduction in either.
Where practical, sidewalks should be graded to drain into front lawns, reducing the total amount
of runoff generated by the roadway. Where practical, walkways may be removed from the
roadway entirely and used to provide access to natural features; see the case studies for more
information. At low design speeds, (10 to 15 mph), sidewalks may be integrated with the road
surface (Burden, 1999).
Bike paths are a nice amenity but also increase cost and imperviousness. Traffic volumes are
low enough on most streets and lanes so as not to require them (Burden, 1999). Bicycle paths
are recommended for larger routes where bicycle trips are more common and vehicle speeds are
higher.
2.4.8 Stormwater Treatment
Open drainage systems enhance stormwater treatment and reduce runoff, and are encouraged
where permitted by soils, slopes and lot configurations. Common treatment systems include dry
swales, grass channels and biofilters. These are typically 1 to 2 feet deep and 7 to 10 feet wide.
See Chapter 3 for more information on these and other stormwater management practices.
2.4.9 Design Speed
Many residential developments have a speed limit of 25 mph; designs for roads in Maui County
are based on this speed. In general, many subdivision designs permit drivers to go faster,
especially where roads are wide and straight. The Uniform Vehicle Code recommends that a
design speed of 30 mph be used for residential developments; ITE recommends 20 to 30 mph,
depending on the grade of the terrain.
Figure 2.5 Example cross-section with open channel.
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-10
Slower vehicle speeds increase public safety, giving drivers more time to react and reducing
the severity of accidents. A design speed of 20 mph should be suitable for most residential
developments (Burden, 1999), and can be encouraged by building narrow, windy roads.
Developments that use geometry to reduce vehicle speeds are also easier for law enforcement
officers to manage.
2.4.10 Minimum Sight Distance
The minimum sight distance at horizontal and vertical curves should be sufficient to allow
drivers to come to a stop at the design speed. At 25 mph, AASHTO recommends 115 feet for
low-volume and 125 feet for high-volume roads. ITE recommends 125 to 200 feet for residential
streets, depending on the grade of the terrain and the design speed.
2.4.11 Maximum and Minimum Grade
To allow for proper drainage, the general standard for the absolute minimum lateral and
longitudinal slopes for roads is 0.5%, and the recommended minimum is 1.0%. Maui County
allows roads to slope at a minimum of 0.25%. In hilly terrain, the road grade should be a
compromise between safety and economics; steeper roads may be cheaper to build but can pose a
safety risk. ITE recommends that the maximum grade for roads in hilly terrain be 15%.
2.4.12 Minimum Centerline Radius
The minimum centerline radius of a road is a function of its design speed and traffic volume, and
of the friction factor of the pavement surface. At 25 mph, AASHTO recommends centerline radii
of 90 to125 feet for ADT less than 250 and 135 to 205 feet for ADT between 250 and 400. ITE
recommends 100 to 200 feet, depending on the grading and design speed of the road.
Larger turn radii can lead to increased vehicle speeds. Radii of 90 to 120 feet can help maintain
vehicle speeds at 20 mph (Burden, 1999).
2.4.13 Length and Radius of Cul-de-sacs
Lanes and ways terminating in a cul-de-sac offer lower vehicle flows and speeds, increasing
quality of life and often creating higher property values. However, such dead end streets offer
reduced access in the time of an emergency and can increase the total impervious area of a
development. Building narrow streets with sharper turns is a preferable alternative to cul-de-
sacs, since it can accomplish the same goal of reducing traffic disturbances, while maintaining
essential connectivity between neighborhoods.
Where cul-de-sacs must be built, they are generally designed for a maximum of 200 ADT. This
is equal to the traffic generated by 20 to 25 houses at 8 to 10 trips per day. Depending on the
density of the development, ITE recommends maximum cul-de-sac lengths between 700 and
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1,500 feet. Cul-de-sacs in Maui County may be no longer than 800 feet in agricultural areas and
550 feet in other areas. Recommending that cul-de-sacs be as short as possible is a good practice
as it may help to reduce their overall use.
A cul-de-sac must be wide enough to accommodate the turning radii of large emergency vehicles
such as fire trucks. Maui recommends a minimum radius of 43 feet and a minimum pavement
width for the access road of 28 feet for urban areas and 22 feet for rural areas (these roads may
be too wide in some cases, as illustrated above). The impervious area can be minimized by
creating a vegetated area in the center, provided that a sufficient paved width is maintained,
(ITE recommends a minimum of 25 feet). Newer fire trucks have reduced turning radii, and the
paved radius may be reduced to 30 to 40 feet in some cases (ASCE, 1990). See Table 2.2 for a
summary of turning radii for AAHSTO design vehicles. Where a vegetated area is used, a 20-
foot paved width may be sufficient for these vehicles (CWP, 1998).
Alternative layouts, such as a tee- or hammer-shaped turnaround, may be appropriate for streets
shorter than 200 feet in length. These areas offer significant reductions in impervious area over
the standard cul-de-sac. A loop road is also a good option; these provide multiple access points
for emergency vehicles and can carry double the traffic volume of a cul-de-sac. Loop roads
also favor the construction of tee-style intersections, which offer numerous benefits (see Section
2.5.16, below).
2.4.14 Intersection Approach Speed and Sight-distance
An intersection approach speed of 20 to 25 mph should allow the motorist to come to a
comfortable stop within 100 feet (ITE, 1997). At increased speeds, greater site distances are
required to allow drivers to recognize approaching obstacles. An appropriate sight distance
triangle must be maintained through building setbacks and reduction in landscaping. AASHTO’s
publications offer a good treatment of this topic.
Table 2.2
Figure 2.6 Common and alternate turnarounds.
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2.4.15 Minimum intersection curb radii
Larger intersection curb radii minimize lane encroachments by turning vehicles, but lead to
an increase in costs, impervious cover, and vehicle speeds. Wide intersections also create an
environment that is less friendly to the pedestrian. Curb radii should be set to the minimum size
required by turning vehicles and lane configurations. AASHTO recommendations range from 15
feet for smaller roads to 25 feet for collector streets.
2.4.16 Intersection Layout
Tee-style intersections offer a number of advantages over crosses, and should be used where
practical. Tee intersections tend to be safer (ITE, 1997), provide attractive terminating vistas,
decrease vehicle speeds, and reduce points of pedestrian-vehicle conflict (Burden, 1999). In
order to minimize conflict between adjacent intersections, tees should be spaced a minimum of
125 feet apart (ITE, 1997). Currently, Maui County recommends that intersections be spaced no
closer than 150 feet.
A sub-collector road with a number of loop roads terminating in tee-style intersections offers a
good opportunity to minimize impervious cover, enhance pedestrian safety and reduce vehicle
speeds, while increasing the overall flow of traffic.
Figure 2.7 Sample layout.
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2.5 Summary
Design criteria are summarized below in Table 2.3:
2.6 Case Study
The Fields at Cold Harbor, Hanover County, Virginia
The Fields at Cold Harbor is a 19 unit residential development in Hanover County, Virginia.
The heavily forested parcel is 120.3 acres in size, includes an existing farm and farmhouse, and
historic military earthworks dating to the Civil War. It is zoned as a Rural Conservation District
(RCD), which allows for the construction of low-density, single family homes, provided that at
least 70% of the site was set aside as conservation area to preserve its rural character.
The development incorporates a number of LID principals, including many that were described
in this chapter. A project based on standard design criteria was drafted during the design phase
for comparison.
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Native plants and trees were conserved using an open space plan and a clustered development,
allowing for 80% of the site to be preserved. Lot sizes were reduced from an average of 2.5
acres in the standard design to a minimum of 1.0 and a maximum of 1.4 acres. Shorter setbacks
and frontages as a result of this design helped to reduce the total length of the roadway. In
addition to these achievements, the project addressed the following road design criteria:
Pavement width:
An 18 foot, shoulder and ditch roadway was used. Standard road designs would have
dictated a 28-foot, curb and gutter road. This choice greatly reduced the total impervious
area in the site and offered dramatic savings in infrastructure.
Parking requirements:
At least two spaces were provided per lot. On street parking was not assumed, which
allowed for a reduction in road width, above. Standard design criteria would have
assumed that parking would occur on both sides of the streets. Eliminating the on-street
parking was a better fit given the site’s rural character.
Figure 2.8 Plan view of the Fields.
LID WORKBOOK: A PRACTITIONER’S GUIDE 2-15
Driveway width and layout:
Two pairs of lots used shared driveways, reducing the total impervious cover of the site.
This would not have been done in the standard design.
Curb requirements:
Curbs were not used, allowing runoff from the road to sheet flow directly into a grass
channel.
Sidewalk and bike path layout:
In the standard design, two 5-foot sidewalks were required. In the final design, these
sidewalks were replaced with a walking trail that provided access to the preserved natural
features of the site. This design choice helped to minimize the impervious cover of the
site, while offering residents an opportunity to better enjoy its amenities.
Stormwater treatment:
Grass channels were used in lieu of the traditional curb and gutter systems. This
provided better treatment than the standard design, reduced peak flows and lowered
infrastructure costs.
The final design was a dramatic improvement to the standard design. In existing conditions,
impervious cover was at 3.3%; this was raised to 7.4% in the final design, down from 8.3% in
the standard design. The open channel design offered better treatment of stormwater and helped
increase the total infiltration rate by 6.4%. Finally, infrastructure costs were nearly cut in half,
totaling $278,000 in the final design and $527,000 in the standard design.
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2.7 References
AASHTO. 2004. A Policy on Geometric Design of Highways and Streets, 5th Edition.
Washington, DC. Available at www.transportation.org.
American Association of State Highway and Transportation Officials (AASHTO). 2001.
Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT ≤ 400).
Washington, DC. Available at www.transportation.org.
Arendt, Randall. 1994. Rural By Design. Co-authors: Brabec, Elizabth A.; Doson, Harry L.;
Reid, Christine; Yaro, Robert D. American Planning Association. Chicago, IL. Available
from the American Planning Association at www.planning.org.
American Society of Civil Engineers. 1990. Residential Streets, 2nd edition. Co-authors:
National Association of Home Builders and Urban Land Institute. Urban Land Institute.
Washington, D.C. Available at www.asce.org.
Burden, Dan. 1999. Street Design Guidelines for Healthy Neighborhoods. Co-authors:
Wallwork, Michael; Sides, Ken; Trais, Ramon; Rue, Harrison Bright. Local Government
Commission Center for Livable Communities. Sacremento, CA. Available at www.lgc.org.
Center for Watershed Protection (CWP). 1998. Better Site Design: A Handbook for Changing
Development Rules in Your Community. Prepared for the Site Planning Roundtable. Ellicot
City, MD. Available at www.cwp.org.
CWP. 2000. Better Site Design: An Assessment of the Better Site Design Principles for
Communities Implementing the Chesapeake Bay Preservation Act. Prepared for the
Chesapeake Bay Local Assistance Department. Ellicot City, MD.
CWP. 1995. Site Planning for Urban Stream Protection. Ellicot City, MD.
Grava, Sigurd. 2003. Options Beyond Inflated Local Street Standards. Urban Planning
Program, Graduate School of Architecture, Planning, and Preservation at Columbia
University. New York, NY.
Institute of Transportation Engineers. 1997. Guidelines for Residential Subdivision Street
Design. Washington, DC. Available at www.ite.org.
National Fire Protection Administration. 2005. NFPA 1 Uniform Code. Prepared by the
Technical Committee on Uniform Fire Code. Las Vegas, NV. Available at www.nfpa.org.
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3 Stormwater Management
3.1 Introduction - Why Stormwater Matters
ortions of the Hawaiian Islands receive a lot of rain, while some areas are very dry.
The average annual rainfall exceeds 300 inches per year in many mountainous areas.
These climatic conditions combined with the region’s unique volcanic and coral geologic
formations, sensitive water resources and significant land development forces make
stormwater a very significant environmental and economic issue.
Historically, stormwater has been viewed as strictly a drainage issue, a waste to be
disposed, and has been routed to the nearest discharge location, infiltrated with little or no
pre-treatment, or conveyed directly to receiving waters via large concrete channels.
Along with development comes an increased amount of impervious surfaces, precluding
the natural infiltration of rainwater into the underlying groundwater system. As a result,
the groundwater “lens” (which serves as the principle drinking water source) is depleted.
Or, in the instances where stormwater is infiltrated without adequate pre-treatment,
groundwater quality is degraded.
In this section, water quality and quantity issues related to stormwater are discussed.
This section also describes sensitive environmental resources areas, such as drinking
water supplies and wetlands.
Impact of Stormwater Runoff on Hawaiian Watersheds
Urban development has a profound influence on the quality of the waters of Hawaii. To
start, development dramatically alters the local hydrologic cycle (see Figure 3.1). The
hydrology of a site changes during the initial clearing and grading that occur during
construction. Trees that had intercepted rainfall are removed, and natural depressions
that had temporarily ponded water are graded to a uniform slope. The spongy humus
layer of the native vegetation that had absorbed rainfall is scraped off, eroded or severely
compacted. Having lost its natural storage capacity, a cleared and graded site can no
longer prevent rainfall from being rapidly converted into stormwater runoff.
The situation worsens after construction. Rooftops, roads, parking lots, driveways and
other impervious surfaces no longer allow rainfall to soak into the ground. Consequently,
most rainfall is directly converted into stormwater runoff. This phenomenon is illustrated
in Figure 3.2, which shows the increase in the volumetric runoff coefficient (Rv) as a
function of site imperviousness. The runoff coefficient expresses the fraction of rainfall
volume that is converted into stormwater runoff. As can be seen, the volume of
stormwater runoff increases sharply with impervious cover. For example, a one-acre
P
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parking lot can produce 16 times more stormwater runoff each year than a one-acre
meadow (Schueler, 1994).
Figure 3.1 Water Balance at Developed and Undeveloped Sites (adapted from
Prince George’s County, 1999)
Figure 3.2 Relationship Between Impervious Cover and Runoff Coefficient
(Schueler, 1987)
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The increase in stormwater runoff can be too much for the natural drainage system to
handle. As a result, the drainage system is often “improved” to rapidly collect runoff and
quickly convey it away (using curb/gutters, enclosed storm sewers, and lined channels).
The stormwater runoff is subsequently discharged to downstream waters, such as
streams, wetlands, lagoons, or near-shore bays.
Impacts to Natural Stream Channels
As pervious rangelands and forests are converted into less pervious urban soils or
pavement, both the frequency and magnitude of storm flows increase dramatically. As a
result, the bankfull event occurs two to seven times more frequently after development
occurs (Leopold, 1994). In addition, the discharge associated with the original bankfull
storm event can increase by up to five times (Hollis, 1975).
Overbank floods are ranked in terms of their statistical return frequency. For example, a
flood that has a 50% chance of occurring in any given year is termed a “two-year” flood.
The two-year storm has been frequently designated as the “bankfull flood,” as researchers
have demonstrated that most natural stream channels on the islands have just enough
capacity to handle the two-year flood before spilling out into the floodplain. This rainfall
depth is termed the two-year design storm. Similarly, a rain event that has a 10% chance
of occurring in any given year is termed a “ten-year storm."
Urban development increases the peak discharge rate associated with a given design
storm because impervious surfaces generate greater runoff volumes and drainage systems
deliver it more rapidly to a stream. The change in post-development peak discharge rates
that accompany development is profiled in Figure 3.3.
Figure 3.3 Hydrographs Before and After Development
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Impacts to Water Quality
Impervious surfaces accumulate pollutants windblown in from adjacent areas, leaked
from vehicles, or deposited from the atmosphere. During storm events, these pollutants
are quickly washed off and rapidly delivered to downstream waters. Water quality
impacts are numerous, and pollutants include sediments (total suspended solids or TSS),
nutrients (nitrogen and phosphorus), and pathogens (bacteria and viruses).
Sediment (Suspended Solids)
Sources of sediment include particles that are deposited on impervious surfaces and
subsequently washed off by a storm event, as well as the erosion of streambanks and
construction sites. Streambank erosion is a particularly important source of sediment,
and some studies suggest that streambank erosion accounts for up to 70% of the
sediment load in urban watersheds (Trimble, 1997).
Both suspended and deposited sediments can have adverse effects on aquatic life in
streams, ponds, and bays. Turbidity resulting from this sediment can reduce light
penetration for submerged aquatic vegetation critical to estuary health. In addition,
the reflected energy from light reflecting off suspended sediment can increase water
temperatures (Kundell and Rasmussen, 1995). Sediment can physically alter habitat
by destroying the riffle-pool structure in stream systems and smothering benthic
organisms. In addition, sediment transports many other pollutants to our water
resources.
Sedimentation is also the most significant threat to the coral reefs around Hawaii.
High sediment loads can kill coral by (1) settling directly on top of corals and
smothering them and (2) inhibiting photosynthesis by reducing the amount of light
which gets through the water column, and (3) providing excess nutrients to the marine
waters through particles that are carried with sediments.
Nutrients
Runoff from developed land has elevated concentrations of both phosphorus and
nitrogen, which can enrich streams, reservoirs, and bays (known as eutrophication).
Significant sources of nitrogen and phosphorus include fertilizer, atmospheric
deposition, sewage (e.g., from overflows and faulty septic systems), animal waste
(both domestic and feral), organic matter, and streambank erosion. Data from
mainland US suggest that lawns are a significant contributor, with concentrations as
much as four times higher than other land uses, such as streets, rooftops, or driveways
(Steuer et al., 1997; Waschbusch et al., 2000; Bannerman et al., 1993). Nutrients are
of particular concern to ponds, lakes, and estuaries and are a major source of
degradation in some of the islands’ waters.
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Bacteria
Bacteria levels in stormwater runoff routinely exceed public health standards for
water contact recreation. Some stormwater sources include pet waste and urban
wildlife. Other sources in developed land include sanitary and combined sewer
overflows, wastewater, and illicit connections to the storm drain system. Bacteria are
a leading contaminant in many of the waters of Hawaii and have led to many beach
closures in recent years.
Environmental Resource Areas and Sensitive Receptors
The Hawaiian Islands contain a broad range of environmental resource areas, which are
sensitive to stormwater discharges. Critical resource areas include groundwater, streams,
ponds, wetlands, beaches and coral reefs. They are impacted by both hydrologic and
water quality aspects of stormwater runoff, as were discussed above. This section
explains the sensitivity of the various resource areas and evaluates their potential
response to alternate stormwater management strategies and practices.
Groundwater
Groundwater serves as the primary source of drinking water to Hawaiians. The only
source of groundwater recharge is precipitation, which infiltrates to the subsurface
and recharges the underlying water table (the upper surface of the groundwater
system). A significant portion of this is lost to evapotranspiration, some is lost to
surface runoff, and the remaining portion is available as “recharge” to groundwater.
As land development occurs, impervious surfaces preclude the natural infiltration of
this rainwater, thereby reducing the recharge rate. This results in a lowering of the
water table, and a reduction of the thickness of the groundwater lens. Ultimately,
development can lead to a depletion of groundwater resources, increased salt water
intrusion to drinking water wells, and increased concentrations of other pollutants
derived from urban runoff.
Water withdrawals for drinking water and irrigation also deplete the groundwater lens
and result in declining water table elevations and corresponding decreases in the
thickness. The Ghyben-Herzberg principle suggests that for each foot that the water
table declines, the lens thickness decreases by 40 feet (based upon the 1:40 density
ratio between fresh and salt water). Therefore, small reductions in recharge and the
water table can significantly affect the groundwater system.
One potential remedy for this “de-watering” impact is to collect stormwater runoff
and to infiltrate it to help restore (or enhance) natural recharge rates. To some degree,
this already occurs in current stormwater management implementation. It is possible
to collect and infiltrate enough stormwater to match the natural (pre-development)
recharge rates. This may be a viable option to mitigate and compensate for other
sources of water consumption and groundwater de-watering, such as groundwater
withdrawals for drinking water and irrigation purposes.
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However, the infiltration of stormwater raises some important water quality issues.
Stormwater is commonly degraded with a broad range of pollutants collected from
the land surface or accompanying precipitation. Secondly, aquifers can be highly
permeable and, therefore, very susceptible to contamination. Thus, depending on the
land use, stormwater can require significant pre-treatment prior to infiltration to
protect the quality of groundwater resources. This may be accomplished with certain
stormwater BMPs that provide comprehensive treatment. Wellhead protection areas
have been delineated showing the specific groundwater areas that contribute to the
pumping water supply wells and require the highest level of protection to ensure a
safe drinking water supply. Currently, recharge is not a requirement for development
sites but can be an effective stormwater management tool if designed properly.
Freshwater Streams, Ponds and Wetlands
There are numerous streams (perennial and intermittent), ponds, and wetlands throughout
Hawaii. They provide important aquatic habitat for a broad range of fish, amphibian,
mammal and bird species, and as recreational resources for humans. In addition, surface
water provides more than 50% of the irrigation water in Hawaii, and in some places, is
the main source of drinking water. Streams are also a source of hydroelectric power and
support certain traditional Hawaiian gathering customs and taro production (Oki, 2003).
Stream flow is derived from overland runoff and baseflow from groundwater, which
discharges into streambeds. If baseflow is continuous throughout the year, the stream is
perennial. If groundwater elevations fall below the natural stream bed elevation, the
stream is intermittent. In either case, stream ecosystems are very dependent upon the
maintenance of natural groundwater levels and corresponding groundwater discharges to
the streams.
Each stream ecosystem is adapted to its natural flow regime, which is a mixture of
surface runoff events and groundwater baseflow. Stormwater management practices
associated with land development within watersheds can significantly alter the timing
and rates of surface flow and groundwater discharge, thereby impacting stream
ecosystems. In some cases, naturally occurring perennial streams may dry up
seasonally in a developed watershed, significantly altering the habitat. Similarly,
water quality impacts caused by increased nutrients and sedimentation can
significantly impact streams ecosystems. Finally, streams, particularly small first-
and second-order streams, are especially susceptible to increased channel erosion
associated with altered hydrology and land development.
Ponds provide unique habitats and are also sensitive to stormwater discharges within their
watersheds. Eutrophication is a common problem in fresh water ponds, and is the result
of excessive phosphorus loading, which can cause excessive weed or algal growth and
ultimately can cause depleted oxygen levels, fish kills, and noxious odors. Although both
phosphorus and nitrogen contribute to excessive plant growth, phosphorus is the limiting
nutrient of freshwater pond environments. Common sources of phosphorus include
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phosphate-containing cleaners or detergents, human and animal waste, and lawn
fertilizers.
Wetlands provide a broad range of habitat and recreational values. They too are
susceptible to impacts from stormwater in terms of both hydrology and water quality
changes. Wetlands are defined and entirely dependent upon surface and near surface
hydrologic conditions (water levels to within 12 inches of the surface of the ground),
which support hydrophytes (wetland vegetation) and hydric soils. Similar to the other
freshwater resource areas discussed above, wetlands are very sensitive to water level
changes and to alterations in water inputs. Therefore, stormwater must be managed
within the watersheds to wetlands in a manner that preserves natural flow regimes.
Wetlands are also susceptible to pollutant loading increases, particularly phosphorus.
Coastal Waters
Coastal waters surround each of the Hawaiian Islands and serve as the ultimate
“discharge area” for all surface runoff. They are valuable for the support and propagation
of shellfish and other marine life, conservation of coral reefs, oceanographic research,
and serve as a very significant recreational resource for humans. Coastal water quality
issues include eutrophication, damage to coral reefs (including sedimentation), and
bacterial/viral pollution of swimming beaches. Sediments cause physical damage
including decreased water clarity and smothering of coral and other marine resources
(Fukuda, 2004). Nutrients (typically nitrogen for coastal environments) cause
eutrophication, which results in excessive algae and weed growth, depleted dissolved
oxygen levels, and foul odors.
3.2 The Concept of Integrated Stormwater Management
Integrated stormwater management design involves the integration of site design practices
and procedures with the design and layout of stormwater infrastructure to attain stormwater
quality and quantity management goals.
The integrated stormwater management concept uses the following elements or steps:
1. Low-impact Development Practices and Techniques – Protect and utilize natural features
of the site to reduce runoff and pollutants. For an overview of low-impact development,
please refer to Chapter 1.
2. Design Criteria for Stormwater Control Requirements – Calculate the volume of runoff to
be controlled for water quality, as described below in Section 3.3. Water quantity shall
be designed to meet local County regulations.
3. Downstream Assessment – If necessary or desired, perform a downstream analysis to
ensure that the proposed development is not adversely impacting downstream properties
after the volumes calculated above have been controlled.
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4. Selection and Sizing of Structural Stormwater Controls and Conveyance – Structural
control measures are selected using a screening process, then sized, designed and
positioned in a development plan. The reader can use the matrices found in Section 3.5
to identify the most appropriate BMP or group of practices to use at a site.
5. Preparation of Final Site Plan – The last step in the process is the preparation of a final
site plan that meets all of the construction and stormwater criteria and preserves or even
enhances the water quality and natural function of the site.
The aim of these steps is to provide a process that will address the comprehensive stormwater
management goals presented in Section 3.3, while at the same time providing ease of
application for the land developer and a streamlined process for the review of a project.
The integrated design process is illustrated in Figure 3.4.
Figure 3.4 The Integrated Stormwater Management Site Design Process
The following principles should be kept in mind in using this process and preparing a
stormwater management plan for a development site:
• Site design should utilize an integrated approach to deal with stormwater quantity, quality
and protection of downstream properties and/or streambanks.
The stormwater management infrastructure for a site should be designed to
integrate drainage and water quantity control, water quality protection and
downstream property and channel protection. Site design should be done in
unison with the design and layout of stormwater infrastructure to attain
stormwater management goals. Together, the combination of better site
design practices and effective infrastructure layout and design can mitigate
the worst stormwater impacts of most urban developments while preserving
water quality and aesthetic attractiveness.
• Stormwater management practices should strive to utilize the natural drainage design
principles and require as little maintenance as possible.
Develop Concept PlanUsing Better SiteDesign Techniques
Use Unified Design Criteria to Determine Control Volumes
Select AppropriateSize, Design and SiteStructural Controls
Prepare Final
Structural ControlsSite Plan
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Almost all sites contain natural features that can be used to help manage and
mitigate runoff from development. Features on a development site might
include natural drainage patterns, depressions, permeable soils, wetlands,
floodplains and undisturbed vegetated areas that can be used to reduce runoff,
provide infiltration and stormwater filtering of pollutants and sediment,
recycle nutrients, and maximize on-site storage of stormwater. Site design
should seek to improve the effectiveness of natural systems rather than to
ignore or replace them. Further, natural systems typically require low or no
maintenance and will continue to function many years into the future.
• Structural stormwater controls should be implemented after site design and nonstructural
options have been exhausted.
Operationally, economically, and aesthetically, conservation site design and
the use of natural techniques offer significant benefits over structural
stormwater controls. Therefore, all opportunities for utilizing these methods
should be explored before implementing structural stormwater controls such
as engineered wet ponds and sand filters.
• Structural stormwater solutions should attempt to be multi-purpose and be aesthetically
integrated into a site’s design.
A structural stormwater facility need not be an afterthought or ugly nuisance
on a development site. A parking lot, soccer field or city plaza can serve as a
temporary storage facility for stormwater. In addition, water features such as
ponds and wetlands when correctly designed and integrated into a site can
increase the aesthetic value of a development.
• “One size does not fit all” in terms of stormwater management solutions.
Although the basic problems of stormwater runoff and the need for its
management remain the same, each site, project and watershed presents
different challenges and opportunities. For instance, an infill development in
a highly urbanized town center or downtown area will require a much
different set of stormwater management solutions than a low-density
residential subdivision in a largely undeveloped watershed. Therefore, local
stormwater management needs to take into account differences between
development sites, different types of development and land use, various
watershed conditions and priorities, the nature of downstream lands and
waters, and community desires and preferences.
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3.3 Stormwater Criteria and Standards
Effective stormwater management needs to address both water quality and water quantity
controls. This requires an integrated approach to applying an appropriate suite of
practices to meet a range of design criteria. This guidance is oriented towards meeting
water quality treatment goals. Consult local County regulations for appropriate quantity
controls.
It is widely recognized that in order to meet various water quality standards and
classifications, some level of stormwater runoff treatment is necessary. There is
conclusive water quality and biological data that show the toxic effect of untreated
nonpoint source pollution. Small-sized, frequently occurring storms account for the
majority of rainfall events that generate urban stormwater runoff. These frequent storms
also account for a significant portion of the annual pollutant loadings. Therefore, by
capturing and treating these frequently occurring smaller rainfall events, it is possible to
effectively mitigate the water quality impacts of stormwater runoff.
Larger storms also have impacts associated with them from channel degradation, surface
erosion, gullying, and flood damage. These impacts can be significantly reduced by storing
and releasing stormwater runoff in a gradual manner that ensures critical erosive velocities
and peak discharges are not exceeded.
Hawaii has seen tremendous population growth and commercial development over the
last several years. Controlling stormwater pollution from development sites is a priority
with regards to stormwater controls and impacts to receiving water bodies. This section
presents recommended general performance standards and treatment criteria for sizing
BMPs to meet pollutant removal objectives at development sites in Hawaii. The focus of
this section is water quality - water quantity criteria are not covered here and vary based on
island and location.
3.3.1 Designation of Stormwater “Hotspot” Land Uses
There are specific conditions where stormwater management and treatment requires an
added level of scrutiny. These conditions are referred to as stormwater “hotspots.”
Discussion of the special considerations warranted for these applications is provided
below.
A stormwater hotspot is defined as a land use or activity that generates higher
concentrations of hydrocarbons, trace metals or toxicants than are found in typical
stormwater runoff, based on monitoring studies. If a site is designated as a hotspot, it has
important implications for how stormwater is managed. First and foremost, stormwater
runoff from hotspots cannot be allowed to infiltrate into groundwater without prior water
quality treatment. Second, a greater level of stormwater treatment is needed at hotspot
sites to prevent pollutant washoff after construction. This will involve preparing and
implementing a stormwater pollution prevention plan (SWPPP) that involves a series of
operational practices at the site that reduce the generation of pollutants from a site or
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prevent contact of rainfall with the pollutants. Visit the USEPA website to learn more
about how to prepare a SWPPP (http://cfpub.epa.gov/npdes/stormwater/swppp.cfm).
Table 3.1 provides a list of designated hotspots for Hawaii. Applicants should prepare a
SWPPP for review and approval by the local authority prior to construction.
Table 3.1 Classification of Stormwater Hotspot Land Uses
The following land uses and activities are considered stormwater hotspots:
• vehicle salvage yards and recycling facilities
• vehicle fueling stations
• vehicle service and maintenance facilities
• vehicle and equipment cleaning facilities
• fleet storage areas (bus, truck, etc.)
• industrial sites
• marinas (service and maintenance)
• outdoor liquid container storage
• outdoor loading/unloading facilities
• public works storage areas
• facilities that generate or store hazardous materials
• commercial container nurseries
• other land uses and activities designated by appropriate permitting authorities of Hawaii
3.3.2 General Performance Standards
To prevent adverse impacts of stormwater runoff, the following performance standards
are recommended for all new development sites and redevelopment sites.
Standard 1 Site designs shall strive to reduce the generation of stormwater
runoff by reducing impervious surfaces and utilizing pervious
areas for stormwater treatment.
Standard 2 Stormwater management shall be provided through a combination
of the use of structural and non-structural practices.
Standard 3 All stormwater runoff generated from new development shall be
adequately treated prior to discharging into jurisdictional wetlands
or inland and coastal waters of Hawaii.
Standard 4 For new development, structural stormwater best management
practices (BMPs) shall be designed to remove 80% of the average
annual post development total suspended solids (TSS) load and
other pollutants as possible (see Section 3.4). It is presumed that a
BMP complies with this performance standard if it is:
1. sized to capture the prescribed water quality volume
(WQv),
2. designed according to the specific performance criteria
outlined in this workbook,
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3. constructed properly, and
4. maintained regularly.
Standard 5 Stormwater discharges to critical areas with sensitive resources
(i.e., coral reefs, beaches, wellhead protection areas, designated
sensitive ecosystems) may be subject to additional performance
criteria, as directed by the appropriate approval authority.
Standard 6 All BMPs shall have an enforceable operation and maintenance
agreement to ensure the system functions as designed. In addition,
every BMP shall have an acceptable form of water quality
pretreatment.
Standard 7 Stormwater discharges from land uses or activities with higher
potential pollutant loadings, defined as hotspots (see Section
3.3.1), are required to use specific structural BMPs and pollution
prevention practices.
3.3.3 Treatment Criteria
The treatment criteria have been determined based on similar work on the mainland, as
well as the local precipitation characteristics. While the methodology is consistent across
all land uses and all receiving water types, the specific sizing requirements are different
for areas of the Hawaiian Islands with differing annual precipitation.
Water Quality Criteria (WQv)
The water quality volume (denoted as the WQv) is intended to improve water quality by
capturing and treating the small, frequently occurring storm events. The WQv is directly
related to the amount of impervious cover created at a site.
The following steps can be used to determine the water quality storage volume WQv:
1. Define Site Area and Impervious Cover
Designers should measure site area and impervious cover directly from the site plan. For
operational purposes, impervious cover (I) is defined as any area of the site that is not
covered by vegetation and is expressed as a percentage.
2. Compute Runoff Coefficient for Site
The volumetric runoff coefficient is defined based on the following equation:
Rv = 0.05 + 0.009 (I)
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3. Determine Appropriate Water Quality Storm (S)
Given that annual rainfall ranges from 10 to almost 500 inches on the Hawaiian Islands,
designers should consult a precipitation map to determine the estimated annual rainfall
for their site. Then, the appropriate water quality storm depth can be selected from Table
3.2 below:
Table 3.2 Water Quality Storm Depth Based on Annual Rainfall (AR)
Zone No. 1 Zone No. 2 Zone No. 3
AR < 25 inches AR 26 to 74 inches AR > 75 inches
S = 0.8 inches S = 1.0 inch S = 1.5 inches
4. Compute Water Quality Volume (WQv)
The Water Quality Volume (WQv) expresses the cubic feet of runoff that must be treated
in an acceptable stormwater treatment practice and is computed as:
WQv = (Rv) (S) (A) (3630)
Where = A = total site area, in acres
5. Select Appropriate Best Management Practice (BMP)
The designer then selects which of the stormwater BMPs can meet the WQv requirement.
The design guidelines for specific practices presented later in this document contain
simple sizing equations to determine how to achieve the WQv at a site.
For facility sizing criteria, the basis for hydrologic and hydraulic evaluation of
development sites should be as follows:
• Impervious cover is measured from the site plan and includes all impermeable
surfaces (i.e., paved roads, driveways and yards, parking lots, sidewalks, rooftops,
patios, and decks).
• The final WQv shall be treated by an acceptable stormwater best management practice
(BMP), with consideration to the management priorities of the given receiving
waters. The list of acceptable BMPs and receiving waters management criteria are
presented in Section 3.4.
• Off-site areas shall be assessed based on their “pre-developed condition” for
computing the water quality volume (i.e., treatment of only on-site areas is required).
However, if an offsite area drains to a proposed BMP, flow from that area must be
accounted for in the sizing of a specific practice.
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3.4 Acceptable Best Management Practices (BMPs)
This section outlines minimum design criteria for five groups of structural best
management practices (BMPs) to meet water quality treatment goals. Some information
for this section was based on work by Schueler (2006) for the County of Maui, Hawaii.
The practice groups include ponds/wetlands, infiltration practices, filtering systems and
open channels. The acceptable practices in this chapter were selected based on the
following criteria:
1. Can capture and treat the full water quality volume (WQv)
2. Are capable of approximately 80% total suspended solids (TSS) removal*
3. Are capable of meeting management objectives for specific resource protection areas
through elevated total phosphorus (TP), total nitrogen (TN) and/or fecal coliform
bacteria (FC) removal**
4. Have acceptable longevity in the field.
* The 80% removal target is a management measure developed by EPA as part of the Coastal Zone
Act Reauthorization Amendments of 1990. It was selected by EPA for the following factors: (1)
removal of 80% is assumed to control heavy metals, phosphorus, and other pollutants; (2) a
number of mainland U.S. states including DE, FL, TX, MA, ME, MD, and VT require/recommend
TSS removal of 80% or greater for new development; and (3) data show that certain BMPs, when
properly designed and maintained, can meet this performance level.
** The TP, TN and FC removal capabilities for those practices that are also capable of removing 80%
TSS will dictate their application for those conditions where additional nutrient and/or bacteria
removal is required.
This chapter also provides minimum design criteria and guidance for structural
management options for pretreatment. Pretreatment BMPs are designed to improve water
quality and enhance the effective design life of practices by consolidating sedimentation
location, but cannot meet the pollutant removal targets. Pretreatment practices must be
combined in a “treatment train” with other water quality BMPs to meet the water quality
criteria.
These design guidelines were developed as a consequence of a reconnaissance of
development and climatic conditions on the island, and with input from local developers,
engineering consultants and municipal staff. The guiding philosophy was to develop:
• Relatively short and simple guidance on a limited number of best management
practices;
• Design criteria that are specifically adapted to work under the unique constraints
and conditions on the islands; and
• Specifications that use construction materials and plant stock that are readily
available on the island.
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3.4.1 Acceptable Water Quality Practice List
Acceptable practices are divided into four broad groups, including:
• Stormwater Ponds/ Practices that have a
Wetlands combination of permanent
pool and extended detention
capable of treating the WQv.
• Infiltration Practices Practices that capture and
temporarily store the WQv
before allowing it to infiltrate
into underlying soils.
• Filtering Practices Practices that capture and
temporarily store the WQv
before passing it through a
filter bed of sand, organic
matter, soil, or other media.
• Open Channel Practices Practices explicitly designed
to capture and treat the full
WQv within dry or wet cells
formed by check dams or
other means, or within the
channel itself through a slow
velocity and relatively long
residence time.
Table 3.3 below lists and describes the BMPs in each of the groups that are acceptable to
capture and treat the full WQv.
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Table 3.3 List of BMPs Acceptable for Water Quality
Group Practice Description
Ponds/Wetlands Micropool Extended
Detention Pond
Pond that treats the majority of the water quality
volume through extended detention, and incorporates
a micropool at the outlet of the pond to prevent
sediment resuspension.
Extended
Detention/Shallow
Wetland
A pond/wetland system that provides a portion of the
water quality volume by detaining storm flows above
the marsh surface.
Wet Extended
Detention Pond
Pond that treats a portion of the water quality volume
by detaining storm flows above the permanent pool
for a specified minimum detention time.
Infiltration
Infiltration
Trenches/Chambers
An infiltration practice that stores the water quality
volume in the void spaces of a limestone aggregate
trench or within an open chamber before it is
infiltrated into underlying soils within the B or C soil
horizons.
Filtering
Practices
Sand/organic Filter
A filtering practice that treats stormwater by settling
out larger particles in a sediment chamber, and then
filtering stormwater through a surface, underground,
or perimeter sand or organic matrix.
Bioretention
A shallow depression that treats stormwater as it
flows through a soil matrix, and is returned to the
storm drain system, or infiltrated into underlying soils
or substratum.
Open Channels Dry Swale
An open vegetated channel or depression explicitly
designed to detain and promote filtration of stormwater
runoff into an underlying fabricated soil matrix.
Oversized Swale
An open vegetated channel designed to trap sediment
above the surface of the swale.
Amended Grass
Channel
An open vegetated channel with thin layer of topsoil,
compost, sand, lime and erosion control fabric to help
establish dense grass cover.
See Section 3.5 for presumed pollutant removals of the practice groups as guidance on
appropriate BMP selection.
Limited design guidance and specifications are provided in this manual for these
practices. In addition, a number of proprietary technologies have been developed to
provide water quality treatment. Some of these have been monitored by independent
sources with mixed results. The U.S. EPA and the U.S. NRCS have developed a joint
manual and website describing these technologies. Individual fact sheets can be
downloaded from the following source
(http://www.epa.gov/NE/assistance/ceit_iti/tech_cos/stor.html).
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3.4.2 Minimum Design Criteria for BMPs
This section presents design criteria for the BMPs listed above for use on the Islands of
Hawaii.
3.4.2.1 Stormwater Ponds/Wetlands
Stormwater ponds are practices that have either a permanent pool of water, or a
combination of a permanent pool and extended detention, and some elements of a
shallow marsh equivalent to the entire WQv. Three design variants include:
• P-1 Micropool* Extended Detention** Pond (Figure 3.5)
• P-2 Extended Detention Shallow Wetland (Figure 3.6)
• P-3 Wet Extended Detention Pond (Figure 3.7)
Treatment Suitability:
All stormwater pond design variations can be used to provide storage for quantity
requirements as well.
NOTE:
Any practice that creates an embankment is required to follow the local dam
requirements. Graphics adopted from CWP, 2002 (Vermont Stormwater Management
Manual).
* Micropool is the term to define a small permanent pool 4-8 feet deep, typically with a minimum storage
of 0.1 inches per impervious acre of drainage.
** Extended detention involves providing temporary storage above the permanent pool or micropool for at
least a portion of the WQv that is released over a specified period of time (i.e., 24 hours).
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Figure 3.5 Micropool Extended Detention Pond (P-1)
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Figure 3.6 Extended Detention Shallow Wetland (P-2)
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Figure 3.7 Wet Extended Detention Pond (P-3)
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Island Adaptations
• The term stormwater pond and wetland are used interchangeably in this guidance.
Ponds generally have deeper permanent pools, while wetlands have shallow ones,
but both pond and wetland design features (along with extended detention) will be
used together in most sites.
• High soil permeability and high annual evaporation rates make it difficult to
maintain a constant permanent pool in many parts of the island; therefore, it is
important to directly address fluctuating water levels in design. Soil infiltration
tests need to be conducted at proposed pond sites to determine the need for a pond
liner, or other methods to address water level fluctuation.
• Pond and wetland design is strongly influenced by annual rainfall. Three pond
designs are proposed based on annual rainfall: micropool extended detention,
shallow wetland extended detention and wet extended detention ponds.
• Stormwater quality ponds can discharge to infiltration basins or perforated pipes
to provide peak discharge control, but need to be a separate, prior cell to assure
full removal of pollutants prior to discharge to groundwater.
Practice Description
Stormwater ponds utilize a combination of permanent pools, shallow wetlands and
temporary extended detention storage to remove pollutants. They are created by
excavating an already existing natural depression or by constructing an embankment.
Runoff from rain events is detained and treated in the pond through gravitational settling
and enhanced biological uptake until it is displaced by runoff from the next storm.
Permanent pools, such as a forebay or micropool, serve to protect deposited sediments
from being resuspended. Temporary storage above the permanent pool may be used for
temporary extended detention. Wetlands plants may colonize shallow water depths from
zero to 9 inches deep.
Pollutants are removed by stormwater ponds through algal uptake, wetland vegetation,
and gravitational settling. Volatilization and chemical activity can also occur, breaking
down and assimilating a number of other stormwater contaminants such as hydrocarbons
Stormwater ponds are a widely applicable for most land uses, and are best suited for
larger drainage areas (e.g., minimum drainage area of 10 to 25 acres depending on annual
rainfall) and local soil infiltration rate). Where feasible, stormwater ponds are a cost-
effective stormwater treatment practices. They are not recommended in ultra-urban areas,
small drainage areas or an on-line location in a stream. With proper design and
maintenance, stormwater ponds can be an attractive and even command a premium on
parcels that are adjacent to them.
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Stormwater ponds are also an effective practice to provide peak discharge control
storage, above the permanent pool (if the discharge is to surface waters). If the discharge
is ultimately to groundwater, the stormwater quality pond must be in a separate, prior cell
to assure full removal of pollutants prior to discharge to groundwater (i.e., a pond within
a pond). Dam safety regulations should be strictly followed with stormwater pond design
to ensure that downstream property and structures are adequately protected.
Stormwater Pond and Wetland Feasibility Factors
Stormwater ponds shall not be located within jurisdictional waters, including wetlands.
In some isolated cases, a permit may be granted to convert an existing degraded wetland
in the context of local watershed restoration efforts. Avoid location of pond designs
within the stream channel, to prevent habitat degradation caused by these structures.
• Annual Rainfall – Water quality sizing varies depending on annual rainfall—See
Table 3.4.
• Drainage Area – Minimum ranges based on annual rainfall from 10 to 25 acres, See
Table 3.4.
• Space Required – Most ponds require about 1-3% of the contributing drainage area
for the footprint of the practice, depending on the average depth of treatment.
• Site Slope – Sloped areas immediately adjacent to the pond should be less than 20%.
Slopes with the pond should be greater than 0.5 – 1% to promote positive flow
through the pond practice
• Minimum Head – Elevation difference needed at a site from the inflow to the outflow
ranges from 3 to 10 feet, depending on the design.
• Minimum Depth to Water Table – In general, there is no minimum separation
distance required with stormwater ponds. In fact, intercepting the groundwater table
is common and helps sustain a permanent pool.
• Soils – Underlying soils of hydrologic group “C” or “D” should be adequate to
maintain a permanent pool. Most group “A” soils and some group “B” soils will
require a liner.
• Mosquito Control – Stormwater ponds can be properly designed, constructed and
maintained to minimize the likelihood of being desirable habitat for mosquito
populations. Designs that incorporate constant inflows and outflows, create habitat
for natural predators, and maintain constant permanent pool elevations limit mosquito
breeding habitat conditions.
• Aesthetics – When ponds and wetlands are integrated early in the site planning
process to provide significant aesthetic appeal to a site that can command additional
lot premiums.
Pond and Wetland Design Features
The design of stormwater ponds and wetlands is strongly influenced by the annual
rainfall present at an island site. Table 3.4 presents three basic design variants for ponds
and wetlands on Hawaiian Islands, along with some of their key design features. In
addition, designers should incorporate the following standard design features into
stormwater ponds and wetlands:
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Inlet Protection
• Flowpaths from the inflow points to the outflow points of stormwater wetlands shall
be maximized.
• Microtopography (complex contours along the bottom of the wetland system,
providing greater depth variation) is encouraged to enhance wetland diversity.
• Each inlet will be served by a forebay unless the inlet provides less than 10% of the
total WQv to the stormwater pond.
• Inlet areas should be stabilized to ensure that non-erosive conditions exist during
events up to the overbank flood event.
• Inlet areas should be stabilized to ensure that non-erosive conditions exist for at least
the 1-year frequency storm event.
• Inlet pipe inverts should generally be located at or slightly below the permanent pool
to limit erosive conditions.
• Reverse slope pipes should draw from at least 12" below the permanent pool.
Table 3.4: Three Design Variants for Island Ponds and Wetlands
DESIGN FACTOR DESIGN NO. 1
(AR < 25 inches)
DESIGN NO. 2
(AR 26 to 74 inches)
DESIGN NO. 3
(AR > 75 inches)
Water Quality
Volume 0.8 inch storm 1.0 inch storm 1.5 inch storm
Recommended
Pond
Design
Micropool
Extended Detention
Pond
Extended
Detention/Shallow
Wetland
Wet Extended
Detention Pond
Permanent Pool (as
a % of WQv)
10% for forebay
and micropool only
30% for forebay,
micropool and
shallow wetland
50% for permanent
pool
24-Hour Extended
Detention Up to 90% of WQv Up to 70% of WQv Up to 50% of WQv
Liner? Yes, if measured infiltration rates exceed 2 inches/hour
Minimum Drainage
Area 25 acres 15 acres 10 acres
Surface Cover Native grass Wetland plants Wetland benches
Sideslopes to Bench 5:1 max 4:1 max 3:1 max
Shoreline Bench 25 feet @ 5% slope 20 feet around pools 15 feet around
pools
Access To forebay, riser
and micropool
To forebay, riser and
micropool
To forebay and
riser
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Adequate Outfall Protection
• The channel immediately below the pond outfall shall be modified to prevent erosion
and conform to natural dimensions in the shortest possible distance, typically by use
of appropriately sized riprap placed over filter fabric that can reduce flow velocities
from the principal spillway to non-erosive levels (3.5 to 5.0 fps).
• Outfalls should be constructed such that they do not increase erosion or have undue
influence on the downstream geomorphology of the stream.
• Flared pipe sections that discharge at or near the stream invert or into a step-pool
arrangement should be used at the spillway outlet.
• If a pond daylights to a channel with dry weather flow, care should be taken to
minimize tree clearing along the downstream channel, and to reestablish a forested
riparian zone in the shortest possible distance.
Stormwater Pond Liners
• When a stormwater pond is located in highly permeable soils (>2 inches/hour
infiltration rate), a liner may be needed to sustain a permanent pool of water. If
geotechnical tests confirm the need for a liner, acceptable options include: (a) six to
12 inches of clay soil (minimum 15% passing the #200 sieve and a minimum
permeability of 1 x 10-5 cm/sec), (b) a 30 ml poly-liner (c) bentonite, (d) use of
chemical additives, or (e) engineering design as approved on a case-by-case basis by
the local review authority.
Sediment Forebay
• A sediment forebay is important for maintenance and longevity of a stormwater pond.
The forebay shall consist of a separate cell, formed by an acceptable barrier. Typical
examples include earthen berms, concrete weirs, and gabion baskets.
• The forebay shall be sized to contain 10% of the water quality volume (WQv), and
shall be four to six feet deep. The forebay storage volume counts toward the total
WQv requirement.
• The forebay shall be designed with non-erosive outlet conditions
• Direct access for appropriate maintenance equipment shall be provided to the forebay.
• A fixed vertical sediment depth marker should be installed in the forebay to measure
sediment deposition over time.
• The bottom of the forebay may be hardened (i.e., concrete, asphalt, grouted riprap) to
make sediment removal easier.
Treatment
• The WQv may be provided by any combination of permanent pool, shallow marsh
and/or extended detention storage
• At least 25% of the permanent pool volume of a stormwater wetland shall be in
deepwater zones with a depth greater than four feet.
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• A minimum of 35% of the total surface area of stormwater wetlands shall have a
depth of six inches or less, and at least 65% of the total surface area shall be
shallower than 18 inches.
• A water balance is recommended to document sufficient inflows to maintain a
constant permanent pool in portions of the island receiving less than 45 inches of rain
per year.
• Permanent pool storage can be provided in multiple cells. Performance is enhanced
when multiple treatment pathways are provided by using multiple cells, longer
flowpaths, high surface area to volume ratios, complex microtopography, and/or
redundant treatment methods (combinations of pool, ED, and marsh). A berm or
simple weir should be used instead of pipes to separate multiple wetland cells.
• The extended detention associated with the WQv shall not extend more than five feet
above the permanent pool or basin floor at its maximum water surface elevation.
• It is generally desirable to provide water quality treatment off-line when topography,
head and space permit. Off-line stormwater management systems are designed to
manage a storm event by diverting a percentage of stormwater events from a stream
or storm drainage system.
Minimum Stormwater Pond Geometry
• The desired length to width ratio for stormwater ponds shall be a minimum 2:1 (i.e.,
length relative to width).
• Microtopography (small irregular 6 to 24 inch variations in bottom topography) is
encouraged to enhance wetland diversity.
• Provide a minimum Drainage Area: Surface Area Ratio of 75:1.
• To the greatest extent possible, maintain a long flow path through the system, and
design ponds with irregular shapes.
Stormwater Pond Benches
• The perimeter of all pool areas greater than four feet in depth shall be surrounded by
two benches:
1. Safety Bench: Except when stormwater pond side slopes are 5:1 (h:v) or
flatter, provide a safety bench that generally extends 10 to 25 feet outward
from the normal water edge to the toe of the stormwater pond side slope (See
Table 3.4). The maximum slope of the safety bench shall be 5%; and
2. Aquatic Bench: Incorporate an aquatic bench that generally extends up to 10
feet inward from the normal shoreline, has an irregular configuration, and a
maximum depth of eighteen inches below the normal pool water surface
elevation.
Landscaping Plan
A landscaping plan shall be provided that indicates the methods used to establish and
maintain vegetative coverage in the pond and its buffer. Minimum elements of a plan
include: delineation of pondscaping zones, selection of corresponding plant species,
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planting plan, sequence for preparing wetland bed (including soil amendments, if needed)
and sources of native plant material.
• Structures such as fascines, coconut rolls, or carefully designed stone weirs can be
used to create shallow marsh cells in high-energy areas of the stormwater pond.
• Wherever possible, wetland plants should be encouraged in a pond design, either
along the aquatic bench (fringe wetlands), the safety bench and side slopes or within
shallow areas of the pool itself.
• The best elevations for establishing wetland plants, either through transplantation or
volunteer colonization, are within six inches (plus or minus) of the normal pool.
• Donor soils for wetland mulch shall not be removed from natural wetlands.
• The landscaping plan should provide elements that promote greater wildlife and
waterfowl use within the stormwater wetland and buffers.
• Woody vegetation may not be planted or allowed to grow within 15 feet of the toe of
the embankment and 25 feet from the principal spillway structure.
Stormwater Pond Buffers and Setbacks
• A buffer should be provided that extends 25 feet outward from the maximum water
surface elevation of the stormwater pond. Permanent structures (e.g., buildings)
should not be constructed within the buffer. Existing trees should be preserved in the
buffer area during construction. The pond buffer shall be contiguous with other
buffer areas that are required by other regulations. An additional setback may be
provided to permanent structures.
• Existing trees should be preserved in the buffer area during construction. It is
desirable to locate forest conservation areas adjacent to ponds. To help encourage
reforestation, the buffer can be planted with trees, shrubs and native ground covers.
• Woody vegetation may not be planted or allowed to grow on an earthen dam
embankment, within 15 feet of the toe of the embankment or 25 feet from the
principal spillway outlet structure.
• The soils in the stormwater buffer are often severely compacted during the
construction process to ensure stability. The density of these compacted soils can be
so great that it effectively prevents root penetration, and therefore, may lead to
premature mortality or loss of vigor. As a rule of thumb, planting holes should be
three times deeper and wider than the diameter of the rootball (of balled and burlap
stock), and five times deeper and wider for container grown stock. Avoid species that
require full shade, or are prone to wind damage. Extra mulching around the base of
the tree or shrub is strongly recommended as a means of conserving moisture and
suppressing weeds.
• Annual mowing of the pond buffer is only required along maintenance rights-of-way
and the embankment. The remaining buffer can be managed as rangeland (mowing
every other year) or forest.
Maintenance Access
• A maintenance right of way or easement shall extend to a stormwater pond from a
public or private road.
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• Maintenance access should be at least 12 feet wide, have a maximum slope of no
more than 15%, and be appropriately stabilized to withstand maintenance equipment
and vehicles. Steeper grades are allowable with stabilization techniques such as a
gravel road.
• The maintenance access should extend to the forebay, safety bench, riser, and outlet
and be designed to allow vehicles to turn around.
Non-clogging Low Flow Orifice
• A low flow orifice shall be provided that is adequately protected from clogging by
either an acceptable external trash rack (recommended minimum orifice of 3") or by
internal orifice protection that may allow for smaller diameters (recommended
minimum orifice of 1").
• The preferred method is a submerged reverse-slope pipe that extends downward from
the riser to an inflow point one foot below the normal pool elevation.
• Alternative methods are to employ a broad crested rectangular, V-notch, or
proportional weir, protected by a half-round CMP that extends at least 12 inches
below the normal pool.
• The use of horizontally extended perforated pipe protected by geotextile fabric and
limestone aggregate is not recommended. Vertical pipes may be used as an
alternative if a permanent pool is present.
Riser in Embankment
• The riser should be located within the embankment for maintenance access, safety
and aesthetics. In addition, the riser should be located so that short-circuiting
between inflow points and the riser does not occur.
• Access to the riser should be provided by lockable manhole covers and manhole steps
within easy reach of valves and other controls.
Pond Drain
• Except where local slopes prohibit this design, each stormwater pond should have a
drain pipe that can completely or partially drain the permanent pool. The drain pipe
should have an elbow or protected intake within the pond to prevent sediment
deposition, and a diameter capable of draining the pond within 24 hours.
Safety
• The principal spillway opening shall not permit access by small children, and
endwalls above pipe outfalls greater than 48 inches in diameter shall be fenced to
prevent a hazard.
• An emergency spillway and associated freeboard shall be provided in accordance
with applicable Hawaii dam safety requirements. The emergency spillway must be
located so that downstream structures will not be impacted by spillway discharges.
• Side slopes to the pond shall not exceed 3:1 (h:v), and shall terminate on a safety
bench.
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• Both the safety bench and the aquatic bench may be landscaped to prevent access to
the pool.
• Warning signs prohibiting swimming may be posted.
• Stormwater pond fencing is generally not encouraged, as the preferred method is to
manage the contours of the stormwater pond to eliminate drop-offs or other safety
hazards.
Pond Maintenance
Maintenance is needed so stormwater ponds continue to operate as designed on a long-
term basis. Some important post construction maintenance considerations are provided
below.
• A legally binding and enforceable maintenance agreement should be executed
between the pond owner and the local review authority.
• Adequate access must be provided for inspection, maintenance, and landscaping
upkeep, including appropriate equipment and vehicles.
• The principal spillway shall be equipped with a removable trash rack, and generally
accessible from dry land.
• Sediment removal in the forebay should occur every 2 to 7 years or after 50% of
total forebay capacity has been lost.
• Sediments excavated from stormwater ponds that do not receive runoff from
confirmed hotspots are generally not considered toxic or hazardous material, and can
be safely disposed by either land application or land filling. Sediment testing may be
required prior to sediment disposal when a hotspot land use is present (see Section
3.3.1 for a list of potential hotspots).
• Periodic mowing of the stormwater buffer is only required along maintenance rights-
of-way and the embankment. The remaining buffer can be managed as a meadow
(mowing every other year) or forest.
• Inspections during construction are needed to ensure that the practice is built in
accordance with the approved design and standards and specifications.
Stormwater pond maintenance activities range in terms of the level of effort and expertise
required to perform them. Routine stormwater pond maintenance, such as mowing and
removing debris or trash, is needed several times each year (See Table 3.5). More
significant maintenance such as removing accumulated sediment is needed less
frequently, but requires more skilled labor and special equipment. Inspection and repair
of critical structural features such as embankments and risers, needs to be performed by a
qualified professional (e.g., structural engineer) that has experience in the construction,
inspection, and repair of these features.
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Table 3.5: Typical Maintenance Inspection Frequencies for Stormwater Pond/Wetlands
Inspection Items Maintenance Items Frequency
Ensure that at least 50% of wetland
plants survive
Check for invasive wetland plants.
Replant wetland vegetation One time - After First Year
Inspect low flow orifices and other
pipes for clogging
Check the permanent pool or dry
pond area for floating debris,
undesirable vegetation.
Investigate the shoreline for erosion
Monitor wetland plant composition
and health.
Look for broken signs, locks, and
other dangerous items.
Mowing – twice a year
Remove debris
Repair undercut, eroded, and
bare soil areas.
Monthly to Quarterly or After
Major Storms (>1”)
Monitor wetland plant composition
and health.
Identify invasive plants
Mechanical components are
functional
Trash and debris clean-up day
Remove invasive plants
Harvest wetland plants
Replant wetland vegetation
Repair broken mechanical
components if needed
Semi-annual to annual
All routine inspection items above
Inspect riser, barrel, and
embankment for damage
Inspect all pipes
Monitor sediment deposition in
facility and forebay
Pipe and Riser Repair
Forebay maintenance and
sediment removal when needed
Every 1 to 3 years
Monitor sediment deposition in
facility and forebay
Forebay maintenance and
sediment removal when needed 2-7 years
Remote television inspection of
reverse slope pipes, underdrains, and
other hard to access piping
Sediment removal from main
pond/wetland
Pipe replacement if needed
5-25 years
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3.4.2.2 Stormwater Infiltration
Stormwater infiltration practices capture and temporarily store the WQv before allowing
it to infiltrate into the soil over a two-day period. Design variants include:
• I-1 Infiltration Trench/Chamber (Figure 3.8)
Treatment Suitability: Infiltration practices typically cannot provide storage for quantity
requirements, except on sites where the soil infiltration rate is greater than 5.0 in/hr.
Extraordinary care should be taken to assure that long-term infiltration rates are achieved
through the use of performance bonds, post construction inspection and long-term
maintenance. Infiltration within geologic formations that may have very high
permeability rates may allow for infiltration of large volumes of stormwater. Applicants
must provide pretreatment of 100% of the WQv prior to direct infiltration into these
formations. Roof runoff can be infiltrated directly, without treatment, and counted
toward WQv requirements.
NOTE: Graphics adopted from CWP, 2002.
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Figure 3.8 Infiltration Trench/Chamber (I-1)
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Island Adaptations
• Most island soils are conducive to rapid infiltration rates, regardless of whether
they are of volcanic or limestone origin. Depending on annual rainfall, up to three
different infiltration designs can be used.
• For water quality purposes, all infiltration trenches need to be in the soil horizon
(i.e., above bedrock) and installed after construction has ceased and the site is
vegetated and stabilized. While underground infiltration is commonly used on the
island to deal with stormwater detention/disposal, infiltration trenches used for
stormwater pollution control must be located within the surface soils.
• Trenches or chambers need to include surface pretreatment cell capable of
keeping sediment and vegetation out of the infiltration cell.
• Due to thin soils and safety considerations, trench depths greater than 5 feet are
not recommended.
• Designers need to measure on-site soil infiltration site, and assess future
operations at the proposed site to determine if they may be a potential stormwater
hotspot. No hotspot runoff can be infiltrated under any circumstances.
Practice Description
An infiltration trench is a rock-filled trench with no outlet that receives stormwater
runoff. Stormwater runoff passes through a pretreatment cell where sediment and organic
matter are trapped before entering the trench. There, runoff is stored in the voids of the
stones, and infiltrates into the underlying soil matrix. Plastic arch chambers or other
comparable perforated storage material can be used in conjunction with stone to increase
the available underground storage. Observation wells are incorporated to monitor
clogging and infiltration rates over time.
Stormwater infiltration trenches capture and temporarily store stormwater before
allowing it to infiltrate into the soil. As the stormwater penetrates the underlying soil,
chemical and physical adsorption processes remove pollutants. Infiltration practices are
suitable for use in residential and other urban areas where measured soil permeability
rates exceed one inch per hour. Infiltration trenches are also suitable for many linear
projects such as roadways. The infiltration trench design uses two surface cells- the first
is used to trap and store sediments while the second is where runoff is infiltrated into the
soil.
Infiltration trenches are primarily used for water quality treatment, but can be connected
to larger underground perforated pipes used to detain peak discharges. Otherwise,
infiltration trenches should either be designed “off-line” using a flow diversion or
designed to safely pass large storm flows while still protecting the infiltration area.
Feasibility of Infiltration at Sites
Sites where infiltration is planned require careful analysis to define design constraints, as
follows:
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• Drainage Area – The contributing area draining to an individual infiltration trench
should be stabilized and less than 2 acres in area.
• Space Required – Varies depending on the depth of the practice. Generally
infiltration trenches are three to five feet deep and less than 25 feet wide.
• Site Slopes –Unless slope stability calculations demonstrate otherwise, infiltration
trenches should be located a minimum horizontal distance of 200 feet from down
gradient slopes greater than 20%. Contributing drainage areas should limit slopes to
15%.
• Practice Slope - Infiltration trench bottoms should be flat to enable even distribution
and infiltration of stormwater. A zero percent longitudinal slope is recommended,
with a maximum longitudinal slope of 1%. Lateral slopes should be 0%.
• Minimum Head – Elevation difference needed at a site to operate an infiltration
trench is nominal- about one foot.
• Minimum Depth to Water Table – Infiltration practices should provide a minimum
vertical distance of 3 feet between the bottom of the infiltration practice and the
seasonal high water table or bedrock layer.
• Soils - Native soils in proposed infiltration areas must have a minimum infiltration
rate of 1.0 inches per hour (typically Hydrologic Soil Group A, with some B soils).
Initially, soil infiltration rates can be estimated from NRCS soil data, and confirmed
with an on-site infiltration evaluation. Native soils should have silt/clay contents less
than 40% and clay content less than 20%. Infiltration practices should not be situated
above fill soils.
• Site Location – Infiltration practices should not be hydraulically connected to
structure foundations or pavement to avoid seepage concerns. At a minimum,
infiltration practices should be located a horizontal distance of 100 feet from any
water supply well, and 35 feet from septic systems or structures.
• Groundwater Protection – Runoff from stormwater hotspots should never be
infiltrated.
• Aesthetics – Infiltration trenches can be effectively integrated into the site planning
process, and aesthetically designed with adjacent native landscaping.
General Design
The design of infiltration trenches is influenced by the annual rainfall and local
infiltration rate, as shown in Tables 3.6 and 3.7.
Table 3.6: Water Quality Volume for Infiltration Based on Annual Rainfall (AR)
Zone No. 1 Zone No. 2 Zone No. 3
AR < 25 inches AR 26 to 74 inches AR > 75 inches
0.8 inch storm 1.0 inch storm 1.5 inch storm
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Table 3.7: Three Design Variants for Island Infiltration Practices
DESIGN FACTOR DESIGN NO. 1
(1.0 - 2.0 inches/hr)
DESIGN NO. 2
(2 to 4 inches/hr)
DESIGN NO. 3
(> 4 inches/hr)
Pretreatment
Volume
25% of WQv
(inclusive)
35% of WQv
(inclusive)
50% of WQv
(inclusive)
Pretreatment Cell
Surface cell at least two feet deep with impermeable liner and
one-inch pea gravel or pumice stone surface with direct access for
maintenance and sediment removal.
Buffer Vegetation Irrigated grass Irrigated grass Grass
Trench Bottom 6” sand layer
Trench Surface Pumice Pea Gravel/
Washed Limestone
Pea Gravel/
Washed Limestone
Observation Well One vertical 6” Schedule 40 PVC perforated pipe, with cap.
Vegetation
Keep adjacent vegetation from forming an overhead canopy over
trench to keep vegetation, fruits and other material from clogging
trench.
Connection to
Underground
Perforated Pipes
Overflow may be directed to perforated pipes after discharge only
if runoff has gone through the pretreatment cell.
Conveyance
• To avoid damage from the erosive velocities of stormwater flows exceeding the
capacity of an infiltration system, an overflow mechanism such as a elevated drop
inlet or flow splitter should be used to redirect flows to an overflow channel or
stabilized water course, and be located off-line from primary storm drain conduits.
• To maintain non-erosive conditions, flows exiting and entering the infiltration
practice should be between 3.5 to 5.0 feet per second.
• Infiltration practices should be sized to fully de-water the entire WQv within 48 hours
after a storm event.
Pretreatment
• Infiltration trenches must include a pretreatment practice, such as a plunge pool,
sump pit, or sediment basin. Depending on the infiltration rate, a proportion of the
water quality volume must be pretreated, as shown in Table 3.7.
• Infiltration trenches can have redundant methods to protect the long-term integrity of
the infiltration rate. Three or more of the following techniques must be installed for
infiltration chambers or trenches: grass channel, grass filter strip (minimum 20 feet
and only if sheet flow is established and maintained), bottom sand layer, upper sand
layer (6” minimum with filter fabric at the sand/limestone aggregate interface), and
use of washed, rounded stone or limestone as aggregate (1/8” to 3/8”).
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• Pretreatment practices should be designed such that exit velocities from the
pretreatment systems are non-erosive and evenly distribute flows across the width of
the practice (e.g., using a level spreader).
Treatment
• Infiltration practices are best used in conjunction with other practices, and often
downstream detention is still needed to meet the quantity requirements.
• Infiltration practices should not be used on sites receiving continuous flow from
groundwater, sump pumps, or irrigation nuisance water.
• The bottom surface area of each practice should be designed to infiltrate the entire
WQv for the area draining to the practice (i.e., sides of the practice should not be
considered in the sizing).
• The bottom of the stone reservoir should be completely flat so that infiltrated runoff
will be able to infiltrate through the entire surface.
• Infiltration trenches should not be deeper than the longest surface area dimension and
should generally not exceed 5 feet in depth.
• A porosity value (Vv/Vt) of 0.4 can be used to design stone reservoirs for infiltration
practices.
• Calculate the surface area of infiltration trenches as:
Ap = Vw / (ndt + fcT/12)
Where:
Ap = surface area (sf)
Vw = design volume (e.g., WQv) (cf)
n = porosity of limestone aggregate fill (assume 0.4)
dt = trench depth (maximum of five feet, and separated at least three
feet from seasonally high groundwater) (ft)
fc = measured infiltration rate (in/hr)
T = time to fill trench (hours) (assumed to be 2 hours for design
purposes)
• Calculate the design volume of infiltration chambers as:
Vw = L*[(w*d*n) – (#*Ac*n) + (#*Ac) + (w*fc*T/12)]
Where:
Vw = design volume (e.g., WQv) (cf)
L = length of infiltration facility (feet)
w = width of infiltration facility (feet)
h = depth of infiltration facility (feet)
# = number of rows of chambers
Ac = cross-sectional area of chamber (see manufacturer’s specifications)
n = porosity (assume 0.4)
fc = infiltration rate (in/hr)
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T = time to fill chambers (hours) (assumed to be 2 hours for design
purposes)
• Infiltration trench aggregate should consist of graded 2 to 5 inch diameter clean,
washed rock with a smaller substrate material (pea gravel or washed, rounded
limestone) and placed above it to prevent the aggregate from clogging. Permeable
filter fabric shall be installed on the trench sides to prevent soil piping, but not on
trench bottom (use sand as filter, instead).
Landscaping
• Infiltration practices should NEVER be installed until all upgradient construction is
completed AND pervious areas are stabilized by dense and healthy vegetation.
• Vegetation associated with infiltration trench buffers should be regularly mowed and
maintained to keep organic matter out of the trench and maintain enough native
vegetation to prevent soil erosion from getting into the trench.
Safety
• Infiltration trenches do not pose any major safety hazards after construction. If an
infiltration trench is greater than five feet deep, OSHA health and safety guidelines
need to be consulted for safe construction practices.
• Fencing of infiltration trenches is neither necessary nor desirable.
Maintenance
Maintenance is a crucial element to ensuring the long-term performance of infiltration
practices. The most frequently cited maintenance problem for infiltration practices is
clogging caused by organic matter and sediment. Common operational problems include:
• Clogging and sediment deposition
• Erosion of contributing land or in channels leading to the practice
• Maintaining appropriate surface vegetation
Table 3.8 provides a summary of common maintenance problems for infiltration
trenches, and Table 3.9 outlines common maintenance activity schedules to prevent them.
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Table 3.8. Typical Maintenance Problems for Infiltration Practices
Problem Comments
Clogging, sediment deposition Key issue for infiltration practice, requires dedicated
pretreatment cell to capture sediments, and sand filter layer
on trench bottom
Surface Vegetation Important to keep woody vegetation from growing over the
surface of the trench.
Erosion from upland areas In these practices, it is important to monitor not only the
practice itself, but also upland infiltration to minimize the
sediment load.
Damage to filter fabric Infrequent but important maintenance concern.
Scouring at Inlet Need to promote non-erosive flows that are evenly
distributed
Access Issues Need surface access to pretreatment and infiltration cells
for regular inspection and maintenance. Observation well is
needed to check for clogging
Several steps in the design and construction of infiltration trenches can increase their
longevity, minimize the maintenance burden and maintain pollutant removal efficiency.
For example, every infiltration trench design should include an observation well
consisting of an anchored six-inch diameter perforated PVC pipe fitted with a cap to
facilitate periodic inspection and maintenance. A legally binding and enforceable
maintenance agreement should be executed between the practice owner and the local
review authority. Adequate access must be provided for all infiltration practices for
inspection, maintenance, and landscaping upkeep, including appropriate equipment and
vehicles. Chambers should not be located underneath pavement unless site constraints
exist.
Infiltration practices are particularly vulnerable to failure during the construction phase
for two reasons. First, if the construction sequence is not followed correctly, construction
sediment can clog the practice. In addition, heavy construction can result in compaction
of the soil, which can then reduce the soil’s infiltration rate. For this reason, a careful
construction sequence needs to be followed. Critical construction elements for
infiltration practices are as follows:
• Avoid excessive compaction- Heavy equipment and traffic should avoid traveling
over the proposed location of the infiltration practice to minimize compaction of
the soil.
• Keep infiltration practices “off-line” until construction is complete- Infiltration
practices should never serve as a sediment control device during site construction
phase and sediment should be prevented from entering the infiltration site
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Table 3.9 Typical Maintenance Activities for Infiltration Trenches
Activity
Schedule
• Replace pea gravel/topsoil and top surface filter fabric (when
clogged).
As needed
• Ensure that contributing area, practice and inlets are clear of
debris.
• Ensure that the contributing area is stabilized.
• Remove sediment and oil/grease from pretreatment devices, as
well as overflow structures.
• Mow grass filter strips should be mowed as necessary. Remove
grass clippings.
• Repair undercut and eroded areas at inflow and outflow structures
Monthly
Check observation wells following 3 days of dry weather. Failure to
percolate within this time period indicates clogging.
• Inspect pretreatment devices and diversion structures for sediment
build-up and structural damage.
• Remove trees that start to grow in the vicinity of the trench.
Semi-annual
Inspection
Clean out accumulated sediments from pretreatment cell Annually
Perform total rehabilitation of the trench to maintain design storage
capacity.
• Excavate trench walls to expose clean soil.
Upon Failure
• Stabilize vegetation before and after construction - excessive sediment loadings
can occur without the use of proper erosion and sediment control practices during
the construction process. Upland drainage areas need to be properly stabilized
with a thick layer of vegetation, particularly immediately following construction,
to reduce sediment loads. If infiltration practices are in-place during construction
activities, diversion berms around the perimeter of the practice and soil
stabilization with vegetation can help protect the practice.
• Correctly install filter fabric on trench sides - large tree roots should be trimmed
flush with the sides of infiltration trenches to prevent puncturing or tearing of the
filter fabric during subsequent installation procedures. When laying out the
geotextile, the width should include sufficient material to compensate for
perimeter irregularities in the trench and for a 6-inch minimum top overlap. The
filter fabric itself should be tucked under the sand layer on the bottom of the
infiltration trench, and stones or other anchoring objects should be placed on the
fabric at the trench sides to keep the trench open during windy periods. Voids
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may occur between the fabric and the excavated sides of a trench. Natural soils
should be placed in any voids to ensure fabric conformity to the excavation sides.
• Establish turf cover ten feet on each side of trench - establishing dense turf on the
sides of the trench to reduce erosion and sloughing, and also provides a natural
means of maintaining relatively high infiltration rates. The use of native grasses
is recommended for seeding primarily due to their adaptability to local climates
and soil conditions. Modest irrigation may be needed in low rainfall zones to
sustain grass cover.
• Inspections during construction are needed to ensure that the infiltration practice
is built in accordance with the approved design and standards and specifications.
Detailed inspection checklists should be used that include sign-offs by qualified
individuals at critical stages of construction to ensure that the contractor’s
interpretation of the plan is acceptable to the designer.
• Effective long-term operation of infiltration practices requires a dedicated and
routine maintenance schedule with clear guidelines and schedules.
3.4.2.3 Stormwater Filtering Systems
Stormwater filtering systems capture and temporarily store the WQv and pass it through a
filter bed of sand, organic matter, or soil. Filtered runoff may be collected and returned
to the conveyance system, or allowed to partially exfiltrate into the soil. Design variants
include:
F-1 Sand Filter (Figure 3.9)
F-2 Organic Filter (Figure 3.10)
F-3 Bioretention (Figure 3.11)
Treatment Suitability: Filtering systems should not be designed to meet runoff quantity
requirements, except under extremely unusual conditions. Filtering practices shall
generally be combined with a separate facility to provide those controls.
NOTE: Graphics adopted from CWP, 2002.
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Figure 3.9 Sand Filter (F-1)
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Figure 3.10 Organic Filter (F-2)
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Figure 3.11 Bioretention (F-3)
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Island Adaptations
• Need a two-cell design to capture sediments prior to treatment in a filtering
practice.
• Thinner filter media depths recommended due to local soils and bedrock
concerns.
• High ET rates make it difficult to attain a vigorous plant cover without irrigation
(which is not a wise use of scarce island freshwater resources).
• Three different bioretention designs proposed that are adapted to different annual
rainfall regimes on island.
• Bioretention areas must be fully protected during construction, and only installed
after entire contributing drainage areas are stabilized.
Filtering practices are suitable for all land uses, so long as the contributing drainage area
is limited to a maximum of about five acres. Sand and organic filters are effective for
treating runoff from urban areas with high pollutant loads and can be incorporated easily
into parking lots. Common bioretention opportunities include landscaping islands, cul-
de-sacs, parking lot margins, commercial setbacks, open space, and streetscapes (i.e.,
between the curb and sidewalk). Bioretention, when designed with an underdrain and
liner is also a good design option for treating potential stormwater hotspots. Bioretention
is extremely versatile because of its ability to be incorporated into landscaped areas.
Water Quality – Filtering practices are excellent stormwater treatment BMPs since they
utilize a variety of pollutant removal mechanisms including vegetative filtering, settling,
evaporation, infiltration, transpiration, biological and microbiological uptake, and soil
adsorption. Filtering BMPs can also be designed as an effective infiltration/recharge
practice, particularly when soil tests indicate an infiltration rate exceeding one inch per
hour.
Peak Discharge Control - To meet quantity control, another structural control (e.g.,
detention) will be necessary in conjunction with a filtering practice. Filters can help
reduce detention requirements for a site by providing elongated flow paths, longer times
of concentration, and volumetric losses from infiltration and evapotranspiration. While
filters are not recommended to provide quantity controls, they can be used to treat the
quality of runoff on the surface before it is discharged to an underground perforated pipe
used for infiltration of peak discharges. Therefore, filtering areas should either be
designed “off-line” using a flow diversion or be designed to safely pass large storm flows
while still protecting the ponding area, mulch layer and any vegetation.
General Site Feasibility
• Sand and organic filtering systems are generally applied to land uses with a high
percentage of impervious surfaces. Sites with imperviousness less than 75% will
require sedimentation pretreatment techniques.
• Drainage Area – 5 acres maximum recommended; 0.5 to 2 acres is preferred. For
larger sites, multiple bioretention areas can be used to treat runoff provided
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appropriate site grading is accurately direct flows to each facility.
• Space Required – Approximately 7-10% of the tributary impervious area is required
for practice footprint; minimum 200 ft2 area for small sites (10 feet x 20 feet)
• Site Slope – Sloped areas immediately adjacent to practice should be less than 20%
but greater than 0.5 – 1% to promote positive flow towards the practice.
• Practice Slope – The slope of the practice surface should not exceed 1% to promote
even distribution of flow throughout practice.
• Minimum Head – A minimum of 3 to 4 feet of elevation difference is needed at a site
from the inflow to the outflow, when an underdrain is used.
• Minimum Depth to Water Table – A separation distance of 3 feet recommended
between the bottom of the filter area and the elevation of the seasonally high water
table if the practice is being used to also infiltrate water. If the practice is only
providing filtration, the separation distance can be eliminated.
• Soils – No restrictions; engineered media required; underdrain is required where
parent soils are classified as Hydrologic Soil Group (HSG) C or D.
• Soil Infiltration rate – In some cases, an on-site test within the proposed infiltration
area is needed to establish the infiltration rate below the infiltration area. One test pit
per 200 sf of filter bed is recommended.
• Groundwater Protection – Do not allow infiltration of runoff from stormwater hotspot
into groundwater.
• Aesthetics – Filtering practice locations should be integrated into the site planning
process, and aesthetic considerations should be taken into account in their siting and
design.
Three Basic Bioretention Designs
The basic bioretention design is modified to account for different levels of annual rainfall
(AR) on the island, as shown in Table 3.10 below:
Table 3.10: Three Design Variants for Island Bioretention
DESIGN FACTOR DESIGN NO. 1
(AR < 25 inches)
DESIGN NO. 2
(AR 26 - 74 inches)
DESIGN NO. 3
(AR > 75 inches)
Water Quality
Volume 0.8 inch storm 1.0 inch storm 1.5 inch storm
Cells Two Two Two
Pretreatment 25% of SA 35% of SA 50% of SA
Underdrain Not required Recommended Required
Surface Cover Washed limestone
or pumice stone Pumice Organic mulch
Vegetation A few planting
holes Trees 15’ o.c. Native trees/shrubs
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Irrigation Only to planting
holes
Short-term to
establish growth Not recommended
Infiltration
Yes, six inch rock
sump below
underdrain
Where soil testing
indicates it is
feasible
Where soil testing
indicates it is
feasible
Surface Overflow?
Elevated drop inlet
above max ponding
height
Yes, safely direct
excess runoff to
surface or SD pipe
Yes, safely direct
excess runoff to
surface or SD pipe
Depth of Media
Filter Min. 2 feet Min. 3 feet Min 4 feet
Connection to
Underground
Perforated Pipes
OK, after full surface WQv treatment in Bioretention area. No
peak discharge credit given for water quality volume
RO = Volumetric runoff
SA = Surface area of bioretention
oc = on center
SD = storm drain pipe
WQv = water quality volume
Conveyance
• If runoff is delivered by a storm drain pipe or is along the main conveyance system,
the filtering practice shall be designed off-line, and a flow splitter or diversion
structure should be provided to divert the WQv to the filtering practice and allow
larger flows to bypass the system.
• Where a flow splitter is not used, contributing drainage areas should be limited to
about 1.0 acre, and an overflow should be provided within the practice to pass a
percentage of the WQv to a stabilized water course or storm drain.
• The overflow associated with the 10- or 25-year storm should be controlled so that
velocities are non-erosive at the outlet point (i.e., prevent downstream slope erosion).
Common overflow systems within the structure consist of a yard drain inlet, where
the top of the yard drain inlet is placed at the elevation of the shallow ponding area.
• A stone drop of about six inches or small stilling basin should be provided at the inlet
of bioretention areas where flow enters the practice through curb cuts.
• Bioretention areas with underdrains should be equipped with a minimum “4”
underdrain diameter in a 1' gravel bed. The porous gravel bed prevents standing
water in the system by promoting drainage. A very permeable filter fabric or graded
stone matrix should be placed between the underdrain layer and the filter media.
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Pretreatment
• Dry or wet pretreatment shall be provided prior to filter media equivalent to at least
25% of the computed WQv. The typical method is a sedimentation basin that has a
length to width ratio of 1.5:1. Sedimentation basins shall have a minimum depth of
3.0 ft. The Camp-Hazen equation is used to compute the required surface area for
sedimentation basins for sand and organic filters requiring pretreatment (WSDE,
1992) as follows:
As = (Qo/W) = Ln (1-E)
where:
As = Sedimentation basin surface area (ft2)
E = sediment trap efficiency (use 90%)
W = particle settling velocity (ft/sec)
use 0.0004 ft/sec for imperviousness
Qo = Discharge rate from basin = (WQv/24 hr)
Equation reduces to
As = (0.066) (WQv) ft2
• Optional pretreatment cells for bioretention area will consist of a minimum one foot
deep surface cell connected to bioretention area with an impermeable filter fabric on
the bottom and a two-inch layer of sand or crushed rock. The cell shall be at least six
inches higher in elevation than the main bioretention.
• Adequate pretreatment for bioretention systems should incorporate all of the
following: (a) grass filter strip below a level spreader or grass channel, (b) washed
limestone aggregate diaphragm and (c) a mulch layer.
• Bioretention should not be used to treat runoff from dirt parking lot or dirt roads due
to a high potential for clogging from sediment.
Treatment
• Sand and organic filter beds typically have a minimum depth of 18". A minimum
filter bed depth of 12" may be approved on a case-by-case basis as demonstrated by
the designer that 18” is not feasible.
• The entire treatment system (including pretreatment) shall be sized to temporarily
hold at least 75% of the WQv prior to filtration.
• The filter area for sand and organic filters should be sized based on the principles of
Darcy’s Law. A coefficient of permeability (k) should be used as follows:
Sand: 3.5 ft/day (City of Austin, 1988)
Peat: 2.0 ft/day (Galli, 1990)
Leaf compost: 8.7 ft/day (Claytor and Schueler, 1996)
Bioretention Soil: 1.0 ft/day for sandy-loam soils
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The required filter bed area is computed using the following equation:
Af = (WQv) (df) / [(k) (hf + df) (tf)]
Where:
Af = Surface area of filter bed (ft2)
df = Filter bed depth (ft)
k = Coefficient of permeability of filter media (ft/day)
hf = Average height of water above filter bed (ft)
tf = Design filter bed drain time (days)
(1.67 days or 40 hours is recommended maximum tf for sand filters; 2
days for bioretention)
• Bioretention should not be used on sites with a continuous flow from groundwater,
sump pumps, or other sources.
• Bioretention systems shall consist of the following treatment components: A
minimum two foot deep planting soil bed (i.e., “filter bed”), a surface cover layer, and
a 9 to 12 inch deep surface ponding area (see Table 3.10). A minimum 12” filter bed
depth may be approved on a case-by-case basis as demonstrated by the designer that
24” is not feasible. In this case, extra organic matter must be added to the soil matrix.
• The filter bed shall be a made soil mixed on-site with the characteristics as shown in
Table 3.11.
• Elevations must be carefully worked out to ensure that the desired runoff flow enters
the facility with no more than the maximum design depth.
Table 3.11. Construction Specifications for Island Bioretention Areas
Pea Gravel/Limestone Clean, double washed stone (#7 or #8)
Underdrain Gravel 3” min clean, double washed # 57 stone over underdrain; 3” addl of
pea gravel/washed limestone on top for filter.
Underdrain Pipe 4” rigid schedule 40 PVC pipe, with 3/8” perforations @ 6” oc, each
underdrain on 1% slope located 20 feet oc from next pipe
Soil Media 50% sand, 30% acceptable topsoil, 20% aged organic leaf compost
derived on island.
Surface Cover Layer of 1 to 3” pumice stone or crushed limestone, OR 2” layer of
shredded tangantangan brush, coconut fronds or banana leaves, aged
at least six months.
Bottom Geotextile Bottom only. Non-woven polyprene geotextile w/ flow rate of > 110
gallons/minutes/square foot (e.g., Geotext 351 or equivalent).
Top Soil Testing to ensure that it has loamy sand or sandy loam texture, with
less than 5% clay content, corrected pH 6 to 7, and organic matter of
at least 2%.
Trees* 12 feet oc, 1” minimum caliper
Shrubs* 8 feet oc
Ground Cover* Buffalograss or kiligrass anchored in erosion control fabric.
*Species selection dependent on design, drought tolerance and commercial availability
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Landscaping
• Sand and organic filters can have a grass cover to aid in pollutant adsorption. The
grass should be capable of withstanding frequent periods of inundation and drought.
• A dense, healthy vegetative cover should be established over the contributing
pervious drainage areas before runoff can be accepted into the practice.
• Landscaping is critical to the performance and function of bioretention areas.
Therefore, a landscaping plan must be provided for bioretention areas.
• General planting recommendations for bioretention areas are as follows:
− Native plant species should be specified over non-native species.
− Vegetation for bioretention areas should be selected based on a specified zone of
hydric tolerance. For example, Design No. 1 should emphasize just a few trees or
shrubs that can tolerate dry conditions (Xeriscapes), and will generally lack
surface cover of turf or vegetation. Design No. 2 also emphasizes a few planting
holes for larger trees and shrubs. Design No. 3 features trees, shrubs and
groundcovers.
− Woody vegetation should not be located at points of inflow.
− Trees should not be planted directly overtop of underdrains and may be best
located along the perimeter of the practice.
− A tree density of approximately one tree per 300 square feet (i.e., 15 feet on-
center) is recommended. Shrubs and herbaceous vegetation should generally be
planted at higher densities (10 feet on-center and 5.0 feet on-center, respectively),
if they can be sustained without supplemental irrigation.
• Filter areas do not pose any major safety hazards, and fencing is generally not needed
or desirable.
Maintenance
Some general bioretention maintenance considerations are provided below, and a more
detailed checklist of maintenance activities and associated timetables is provided in Table
3.12.
• Organic filters or sand filters that have a grass cover should be mowed a minimum of
three times per growing season to maintain maximum grass heights less than 12
inches.
• A legally binding and enforceable maintenance agreement should be executed
between the practice owner and the local review authority to ensure the following:
- Sediment shall be cleaned out of the sedimentation chamber when it accumulates
to a depth of more than 12 inches. Vegetation within the sedimentation chamber
shall be limited to a height of 18 inches. The sediment chamber outlet devices
shall be cleaned/repaired when drawdown times exceed 36 hours. Trash and
debris shall be removed as necessary.
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- Silt/sediment shall be removed from the filter bed when the accumulation
exceeds one inch. When the filtering capacity of the filter diminishes
substantially (i.e., when water ponds on the surface of the filter bed for more
than 48 hours), the top few inches of discolored material shall be removed and
shall be replaced with fresh material. The removed sediments shall be disposed
in an acceptable manner (i.e., landfill).
• Adequate access must be provided for all filtering facilities for inspection,
maintenance, and landscaping upkeep.
• The surface of the ponding area may become clogged with fine sediment over time.
Core aeration or cultivating of unvegetated areas may be required to ensure adequate
filtration.
• All filtering areas must be covered by a drainage easement to allow inspection and
maintenance. If filtering area is located in a residential area, the existence and
purpose of the BMP shall be noted on the deed of record.
• The most frequently cited maintenance concern for filtering BMPs is surface and
underdrain clogging caused by vegetation, organic matter, sediment, hydrocarbons,
and algal matter. Common operational problems include:
− standing water
− clogged filter surface
− broken observation wells
− inlet, outlet or underdrains clogged
• Effective long-term operation of filtering practices requires dedicated and routine
maintenance tasks performed on consistent timetable.
Table 3.12 Recommended Maintenance Activities for Bioretention Areas
Activity
Schedule
• Pruning and weeding to maintain appearance.
• Mulch replacement when erosion is evident.
• Remove trash and debris.
As needed
• Inspect inflow points for clogging (off-line systems). Remove
any sediment from pretreatment cell.
• Inspect trees and shrubs for survival and replace any dead or
severely diseased vegetation.
Semi-annually
• Inspect and remove any sediment and debris build-up in
pretreatment areas.
• Inspect inflow points and bioretention surface for build up of
sediments
Annually
• Replace mulch if used for surface cover area.
• Replace pea gravel diaphragm or filter fabric if warranted.
• The planting soils should be tested for pH to establish acidic
levels. If the pH is below 5.2, limestone should be applied. If the
pH is above 7.0 to 8.0, then iron sulfate plus sulfur can be added
to reduce the pH.
2 to 3 years
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Many design features can minimize the maintenance burden and maintain pollutant
removal efficiency. Key examples include: limiting drainage area, providing easy site
access, providing pretreatment, and utilizing native plantings.
The construction phase is another critical step where many maintenance problems can be
minimized or avoided. The most important maintenance guideline to follow during
construction is to make sure that the contributing drainage area has been fully stabilized
prior to bringing the practice “on line.”
Inspections during construction are needed to ensure that the filtering practice is built in
accordance with the approved design and standards and specifications. Detailed
inspection checklists should be used that include sign-offs by qualified individuals at
critical stages of construction, to ensure that the contractor’s interpretation of the plan is
acceptable to the professional designer.
3.4.2.4 Open Channel Systems
Open channel systems are vegetated open channels that are explicitly designed to capture
and treat the full WQv within dry or wet cells formed by check dams or other means.
Designs include:
• O-1 Dry Swale (Figure 3.12)
• O-2 Oversized Swale
• O-3 Amended Grass Channel
Oversized swales and amended grass channels are design variants of the dry swale.
Treatment Suitability: Open Channel Systems can meet water quality treatment goals
only.
NOTE: Graphic adopted from CWP, 2002.
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Figure 3.12 Dry Swale (O-1)
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Island Adaptations
• Thin, nutrient poor soils with low water holding capacity make it difficult for dense
vegetative cover to become established on new swales
• In leeward portions of the island where annual rainfall is low and ET rates are high, it
may not be possible to maintain dense grass cover without supplemental irrigation,
which is an unwise use of scarce freshwater resources.
• The contributing drainage areas to most swales will have exposed soils that are prone
to erosion, so island swales need to be designed to accommodate a high sediment
load.
General Description
Swales can be used either for pretreatment or as a stand alone water quality practice. All
swale designs are generally located adjacent to paved surfaces and with stabilized
drainage areas that have a slope less than 5%. Three kinds of swales can be used
depending on amount of annual rainfall: oversized swales with check dams, amended
grass channels and engineered dry swales (Table 3.13).
Dry swales act as a filtering device, and contain 18 to 24 inches of filter media
below the bottom of the swale, and an underdrain when underlying soils have an
infiltration rate of less than 0.5 inches per hour.
Oversized swales provide sediment trapping capacity above the surface of the
swale, and may not be able to consistently maintain dense vegetative cover.
Amended grass channels include a thin layer of topsoil, compost, sand, lime and
erosion control fabric to create better start up conditions to establish dense grass
cover. Depending on slope, amended grass swales may contain coir fiber log
check dams to temporarily retain runoff, and enable greater infiltration.
All three swale designs are an excellent practice to remove pollutants through filtering
and settling, evaporation, infiltration, transpiration, biological and microbiological
uptake, and soil adsorption. Grass channels and dry swales can be designed to promote
additional infiltration when parent soils have good permeabilities (i.e., infiltration rates >
1.0 in/hr).
Swales with greater than 5% slope should be designed following road construction
guidelines for ESC control. This normally entails the use of water bars, cross drains,
broad-based dips and sediment traps with defined storage capacity to prevent erosion.
Swales are suitable for most low density land uses, so long as they have limited
contributing drainage (e.g., typically less than 5 acres) and meet acceptable slope
conditions. Swales can be incorporated into landscaped areas. Swales generally cannot
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provide quantity controls but must be designed to safely pass large storm flows without
eroding the swale. Swales can help reduce detention requirements at a site by elongating
flow paths, increasing time of concentration, and reducing runoff volumes.
Table 3.13: Three Design Variants for Island Swales
DESIGN FACTOR DESIGN NO. 1
(AR < 25 inches)
DESIGN NO. 2
(AR 26 - 74 inches)
DESIGN NO. 3
(AR > 75 inches)
Water Quality
Volume 0.8 inch storm 1.0 inch storm 1.5 inch storm
Swale Design
Over-sized swales
w/ check dams
Amended grass
channels Dry swales
Surface Cover Dirt w/ sparse
vegetative cover Grass & ECF Grass
Soil Media?
No Yes, 3 inches Yes, 18+ inches
Erosion Control
Fabric? No Yes
Check Dams? Yes Depends on Slope
and Infiltration Rate
When slope is more
than 3%
Dugouts? Yes No No
Infiltration
Testing? No Yes Yes
Soil Testing? No Yes No
Underdrain? No No Yes, if fc< 1 inch/hr
General Feasibility for Swales
• Annual Rainfall: not recommended as primary BMP when AR is less than 25 inches
• Slope: All swales should have maximum slopes of 5% and minimum slopes of 0.5%.
• Drainage Area – 5 acres maximum recommended; 1 to 2 acres is preferred.
• Space Required – Function of available head at site
• Head: One foot minimum (grass channel) 3 feet minimum for dry swale
• Minimum Depth to Water Table – A separation distance of at least 2 feet is
recommended between the bottom elevation of the swale and the seasonally high
water table, unless swale is designed as a linear wetland.
General Design Criteria for all Swales
• The general shape of swales shall be parabolic or trapezoidal to provide maximum
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width for runoff to be filtered and infiltrated.
• Swales that have a grass cover should be mowed as needed during the growing season
to maintain maximum grass heights less than 12 inches.
• In addition, flows within the swale associated with the 10-year, one-hour storm
should be controlled so that velocities are non-erosive.
• Pretreatment for swales should consist of plunge pools where concentrated flows
enter and with level spreaders where lateral flows enter.
• Swales should have gentle side slopes (no more than 3:1 horizontal: vertical).
• A dense and vigorous vegetative cover should be established over the contributing
pervious drainage areas before runoff can be accepted into a grass channel or dry
swale. Ground cover with the swale should be capable of withstanding frequent
periods of inundation and drought.
Design Criteria for Oversized Swales with Check Dams
• These swales are primarily used in low rainfall areas of the island where it is difficult
to maintain grass cover without supplemental irrigation. These designs utilize dugouts
behind low check dams in the swale to provide the requisite WQv. It is strongly
recommended that twice the normal WQv be provided to provide capacity for future
sediment deposition.
• Check dams can be composed of stone, logs, lumber or coir fiber logs, and must be
firmly anchored into the sideslopes to prevent outflanking. The designer should
ensure the check dam will be stable during the design storm event
• The height of the check dam relative to the normal channel elevation should not
exceed two feet.
• Each check dam should have a weephole or similar drainage feature so it can dewater
after storms. Armoring may be needed behind the check dam to prevent erosion, and
the check dam shall be designed to spread runoff evenly over the surface
• Dugouts up to two feet deep may be provided in front of the swale to provide
additional water quality volume. Direct access should be possible to each dugout to
remove trapped sediments.
Design Criteria for Amended Grass Swales
This design is intended for portions of the island with moderate annual rainfall, but
difficult soil conditions to maintain a dense grass cover. The bottom of the swale is
amended with several inches of soil media anchored by a decomposable erosion control
fabric (ECF). The soil media consists of a combination of topsoil, compost and lime, and
is adjusted based on soil analysis. Infiltration testing is needed to determine whether the
WQv can be met through filtering and infiltration alone without providing surface
storage. Table 3.14 presents a simple guide for making this decision for various
combinations of swale slopes and measured soil infiltration rates.
• If check dams are needed, staked coir fiber logs or equivalent check dams need to be
installed to attain the desired WQv.
• Erosion control fabrics should utilize natural and decomposable fabrics such as
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shredded coconut fiber or coir, and be firmly anchored in place.
• Swale soils must be tested to determine the nature of the soil amendment. At a
minimum, the soils should be tested for nutrient requirements, acidity, and water
holding capacity. In addition at least one infiltration test should be conducted per
every 100 feet of swale.
• Designers should adjust the dimensions of the swale (bottom width and slope) to
achieve the greatest contact time.
• Designers should select the most appropriate warm season grass species suited for site
conditions. CTHAR NM-4 provides a useful guide to Hawaii grasses with respect to
drought and shade tolerance, nutrient requirements, and maintenance needs.
Table 3.14: Conditions where Check Dams (CD) are needed to get Surface WQv
Storage
Swale Slope Infiltration
Rate (in/hr) 0.5 to 1% 1 to 2 % 2 to 3% 3 to 4 % 4 to 5%
0 to 0.5 CD CD CD CD CD
0.5 to 1.0 CD CD CD CD
1.1 to 2.0 CD CD CD
2.0 to 4.0 CD CD
4.1 or greater CD
Design Criteria for Dry Swales
This design is for higher rainfall areas on the island. The dry swale contains a deeper bed
of soil media that acts as filter, and may also have an underdrain enclosed in a gravel
jacket if soil infiltration rates are less than one inch per hour. The basic design criteria
for dry swales are outlined in Schueler and Claytor (1996). The following adaptations
are recommended for Hawaii.
• The minimum depth of the soil media can be 18 inches, if soils are relatively
permeable.
• The media should be the same composition as that used for bioretention areas.
• Check dams are only needed when slopes exceed 3%.
Conveyance
• The peak velocity for the 2-year storm must be non-erosive (i.e., 3.5-5.0 fps).
• Open channels shall be designed to safely convey the 10-year, 1-hour storm with a
minimum of 6 inches of freeboard.
• The maximum allowable temporary ponding time within a channel shall be less than
48 hours. An underdrain system shall be used in the dry swale to ensure this ponding
time.
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• Channels shall be designed with moderate side slopes (flatter than 3:1) for most
conditions. Designers may utilize a 2:1 maximum side slope, where 3:1 slopes are
not feasible.
• Open channel systems which directly receive runoff from non-roadway impervious
surfaces may have a 6-inch drop onto a protected shelf (washed, rounded limestone
aggregate diaphragm) to minimize the clogging potential of the inlet. Runoff from
roads shall drain over a vegetative slope prior to flowing into a swale.
• The underdrain system should be composed of a 6" limestone aggregate bed with a 4"
PVC pipe.
Pretreatment
• Provide 10% of the WQv in pretreatment. This storage is usually obtained by
providing check dams at pipe inlets and/or driveway crossings. Road drainage
entering a swale along the length of the road may pre-treat runoff using a vegetative
filter strip. An effective filter strip shall be no steeper than 6% slope and 4 feet wide
for each travel lane draining to the swale.
• Utilize a washed, rounded limestone aggregate diaphragm and gentle side slopes
along the top of channels to provide pretreatment for lateral sheet flows.
Treatment
• Temporarily store the WQv within the facility to be released over a minimum 30-
minute duration.
• Design with a bottom width no greater than 8 feet to avoid potential gullying and
channel braiding, but no less than two feet.
• Open channels should maintain a maximum ponding depth of one foot at the mid-
point of the channel, and a maximum depth of 18" at the end point of the channel (for
storage of the WQv).
Landscaping
• Landscape design should specify proper grass species and wetland plants based on
specific site, soils and hydric conditions present along the channel. (See Section 3.6
for landscaping guidance for Hawaii).
Maintenance
• A legally binding and enforceable maintenance agreement shall be executed between
the facility owner and the local review authority to ensure the following:
- Sediment build-up within the bottom of the channel or filter strip is removed
when 25% of the original WQv volume has been exceeded.
- Vegetation in dry swales is mowed as required to maintain grass heights in the 4
to 6 inches range, with mandatory mowing once grass heights exceed 10”.
In general, the oversized swales with check dams will tend to have the greatest
maintenance burden since sediments will need to regularly be cleaned out. Effective
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long-term operation of swales requires routine maintenance performed on a defined
timetable. Some important maintenance considerations are provided in Table 3.15.
Table 3.15 Recommended Maintenance Activities for Swales
Activity
Schedule
• If swale is clogged or partially clogged, manual manipulation of
the surface layer of sand may be required. Remove the top few
inches of media, roto-till or otherwise cultivate the surface, and
replace media with like material meeting the design
specifications.
• Initial irrigation may be needed to establish grass cover.
As needed
• Ensure the swale is clear of debris.
• Mow the swale at least four times a year
• Check to ensure that the filter surface is not clogging (also check
after storms greater than about 1”).
Monthly
• Check to see that the dugouts, check dams and swale are clean of
sediment and remove as necessary.
• Inspect check dams to ensure good condition and no evidence of
erosion.
• Re-seed bare patches.
• Stabilize any eroded areas.
• Ensure that flow is not bypassing the swale.
Annually
The construction phase is another critical step where maintenance problems can be
minimized or avoided. As with other practices, the most critical construction requirement
is to ensuring the contributing drainage area has been fully stabilized prior to bringing the
swale “on line”. Inspections during construction are needed to ensure the swale is
installed in accordance with the approved design and standards and specifications.
Detailed inspection checklists should be used that include sign-offs by qualified
individuals at critical stages of construction, to verify the contractor’s interpretation of
the plan is acceptable with the designer.
3.5 Selecting the Most Effective Stormwater Treatment System
The selection of appropriate stormwater practices for any given site involves a
combination of the process of elimination and the process of addition. Typically, no
single practice will meet all stormwater management objectives. Instead, a series of
practices are generally required. Certain practices can be eliminated from consideration
based on one limiting factor. But several practices may ultimately “survive” the
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elimination process. The most appropriate practices are those that are both feasible, cost
effective, and achieve the maximum benefits for watershed protection.
Structural stormwater practices are frequently designed to meet either water quality
and/or water quantity control requirements. Water quality facilities are typically applied
to control and treat pollutants that wash off urban land surfaces and are designed for a
prescribed volume of runoff, which is usually relatively small and is called the water
quality volume (WQv), as described in Section 3.3.3. Water quantity facilities are
typically designed to control increases in peak flow rates and volumes associated with
larger storms typically of the 10-year frequency, 1-hour storm up to the 100-year storm,
depending on site location and drainage area.
This section presents a series of matrices that can be used as a screening process for
selecting the best BMP or group of BMPs for a development site. It also provides
guidance for locating practices on the site. The matrices presented can be used to screen
practices in a step-wise fashion. Screening factors include:
• Land Use
• Physical Feasibility
• Watershed
• Stormwater Management Capability
• Pollutant Removal
• Community and Environmental
The six matrices presented here are not exhaustive. Specific additional criteria may be
incorporated depending on local design knowledge and resource protection goals.
Caveats for the application of each matrix are included in the detailed description of each.
More detail on the proposed step-wise screening process is provided below:
Step 1 Land Use
Which practices are best suited for the proposed land use at this site? In this step, the
designer makes an initial screen to select practices that are best suited to a particular land
use or to exclude those practices that are ill suited for certain land uses. For example,
infiltration practices should not be utilized where runoff is expected to contain high levels
of dissolved constituents, such as metals or hydrocarbons or where prior subsurface
contamination is evident. Increased hydraulic loading to contaminated soils can
accelerate pollutant migration and/or leaching into underlying groundwater.
Step 2 Physical Feasibility
Are there any physical constraints at the project site that may restrict or preclude the use
of a particular BMP? In this step, the designer screens the BMP list using Matrix No. 2
to determine if the soils, water table, drainage area, slope or head conditions present at a
particular development site might limit the use of a BMP. For example, stormwater
ponds/wetlands generally require a drainage area approaching 25 acres unless
groundwater interception is likely, and can consume a significant land area.
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Step 3 Watershed
What watershed protection goals need to be met in the resource my site drains to?
Matrix No.3 outlines BMP goals and restrictions based on the resource being protected.
This set of factors involves screening out those practices that might contradict overall
watershed protection strategies, or eliminating management requirements where they are
unnecessary or inappropriate. For example, practices that maximize pollutant and
toxicity reduction are typically relevant in urban watersheds and water quantity controls
are not necessary for discharges to tidal waters or large river systems. Regulatory
requirements under the Clean Water Act, Total Maximum Daily Load (TMDL) reduction
requirements and/or interests from watershed associations may dictate the type, location,
and design requirements for stormwater management practices.
Step 4 Stormwater Management Capability
Can one BMP meet all design criteria, or is a combination of practices needed? In this
step, designers can screen the BMP list using Matrix No. 4 to determine if a particular
BMP can manage a wide range of storm frequencies. For example, the filtering practices
are generally limited to water quality treatment and seldom can be utilized to meet larger
stormwater management objectives. At the end of this step, the designer can screen the
BMP options down to a manageable number and determine if a single BMP or a group of
BMPs are needed to meet stormwater sizing criteria at the site.
Step 5 Pollutant Removal
How do each of the BMP options compare in terms of pollutant removal? In this step,
the designer views removal of select pollutants to determine the best BMP options for
water quality. Some practices have a better pollutant removal potential than others or
have a better capability to remove certain pollutants. For example, stormwater
ponds/wetlands provide excellent total suspended solids (TSS) removal but only modest
total nitrogen (TN) removal.
Step 6 Community and Environmental
Do the remaining BMPs have any important community or environmental benefits or
drawbacks that might influence the selection process? In this step, a matrix is used to
compare the BMP options with regard to maintenance, habitat, community acceptance,
cost and other environmental factors. Some practices can have significant secondary
environmental impacts that might preclude their use in certain situations. Likewise, some
practices have frequent maintenance and operation requirements that are beyond the
capabilities of the owner. For example, infiltration practices are generally considered to
have the highest maintenance burden because of a high failure history and consequently,
a higher pre-treatment maintenance burden and/or replacement burden. Infiltration
practices should not be used where prior subsurface contamination is present due to the
increased threat of pollutant migration associated with increase hydraulic loading from
infiltration systems.
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3.5.1 Step 1 - Land Use
This matrix allows the designer to make an initial screen of practices most appropriate for
a given land use.
Rural. This column identifies BMPs that are best suited to treat runoff in rural or very
low density areas (e.g., typically at a density of less than ½ dwelling unit per acre).
Residential. This column identifies the best treatment options in medium to high density
residential developments.
Roads and Highways. This column identifies the best practices to treat runoff from major
roadway and highway systems.
Commercial Development. This column identifies practices that are suitable for new
commercial development.
Hotspot Land Uses. This column examines the capability of BMPs to treat runoff from
designated hotspots. BMPs that receive hotspot runoff may have design restrictions, as
noted.
Ultra-Urban Sites. This column identifies BMPs that work well in the ultra-urban
environment, where space is limited and original soils have been disturbed. These BMPs
are frequently used at redevelopment and infill sites.
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Table 3.16 BMP Selection Matrix 1-Land Use
BMP Group BMP Design Rural Residential Roads and
Highways
Commercial/
High Density
Hotspots Ultra
Urban
Micropool ED | | | 1 z
ED Wetland | | 1 z
Pond/
Wetland
Wet ED Pond | | | 1 z
Infiltration Infiltration
Trench/Chambers | | z
Filters Sand Filter z z | 2 |
Organic Filter z | | 2 |
Bioretention | | 2 |
Open
Channels
Dry Swale | | 2
Oversized Swale | | 2
Amended Grass
Channel | | 2
|: Yes. Good option in most cases.
: Depends. Suitable under certain conditions, or may be used to treat a portion of the site.
z: No. Seldom or never suitable.
1: Acceptable option, but may require a pond liner to reduce risk of groundwater
contamination.
2: Acceptable option, if not designed as an exfilter. (An exfilter is a conventional stormwater
filter without an underdrain system. The filtered volume ultimately infiltrates into the
underlying soils.)
3.5.2 Step 2 - Physical Feasibility
This matrix allows the designer to evaluate possible options based on physical conditions
at the site. More detailed testing protocols are often needed to confirm physical
conditions at the site. Five primary factors are:
Soils. The key evaluation factors are based on an initial investigation of the NRCS
hydrologic soil groups at the site. Note that more detailed geotechnical tests are usually
required for infiltration feasibility and during design to confirm permeability and other
factors.
Water Table. This column indicates the minimum depth to the seasonally high water
table from the bottom elevation, or floor, of a BMP.
Drainage Area. This column indicates the minimum or maximum drainage area that is
considered optimal for a practice. If the drainage area present at a site is slightly greater
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than the maximum allowable drainage area for a practice, some leeway is warranted
where a practice meets other management objectives. Likewise, the minimum drainage
areas indicated for ponds and wetlands should not be considered inflexible limits, and
may be increased or decreased depending on water availability (baseflow or
groundwater), mechanisms employed to prevent clogging, or the ability to assume an
increased maintenance burden.
Slope. This column evaluates the effect of slope on the practice. Specifically, the slope
guidance refers to how flat the area where the practice is installed must be and/or how
steep the contributing drainage area or flow length can be.
Head. This column provides an estimate of the elevation difference needed for a practice
(from the inflow to the outflow) to allow for gravity operation.
Table 3.17 BMP Selection Matrix 2-Physical Feasibility
BMP Group BMP
Design
Soils Water
Table
Drainage
Area (Ac)
Site
Slope
Head
(Ft)
Pond Micropool ED 10 min**
ED/Shallow
Wetland
Wet ED Pond
Limestone
and HSG A
soils require
pond liner
3 foot*
separation if
hotspot or
aquifer
25 min**
No more
than 20% 3 to 10 ft
Infiltration Infiltration
Trench/Chamber
fc > 0.5*
inch/hr 3 feet* 5 max No more
than 20% 1 ft
Filters Sand Filter 10 max *** 2 to 7 ft
Organic Filter OK 2 to 4 ft
Bioretention Made Soil
2 feet 5 max***
no more
than 20%
5 ft
Open Channels Dry Swale Made Soil 2 feet 5 max 3 to 5 ft
Oversized Swale Made Soil 2 feet 5 max 1 ft
Amended Grass
Channel Made Soil 2 feet 5 max
No more
than 5%
1 ft
Notes: OK= not restricted, WT= water table, PT = pretreatment, fc =soil permeability
* denotes a required limit, other elements are planning level guidance and may vary somewhat
depending on site conditions or design variants.
** unless adequate water balance and anti-clogging device installed
***drainage area can be larger in some instances.
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3.5.3 Step 3 - Watershed
The design and implementation of stormwater management control measures is strongly
influenced by the nature and sensitivity of the receiving waters. In some cases higher
pollutant removal, more recharge or other environmental performance is warranted to
fully protect the resource quality, human health and/or safety. Based on the discussions
in Section 3.1, critical resource areas include: groundwater, freshwater streams, ponds,
wetlands, and coastal waters. Table 3.18 presents the key design variables and
considerations that must be addressed for sites that drain to any of the above critical
resource areas.
Table 3.18 BMP Selection Matrix 3-Watershed
Critical Resource Area Specific Criteria
BMP Group Groundwater Freshwater
Streams
Freshwater
Ponds
Freshwater
Wetlands
Coastal Waters
Ponds/Wetlands Pre-treat
hotspots.
Provide 2' SD
from seasonal
high
groundwater
elevation
Pretreat
hotspots at
100% of WQv.
OK, quantity
control
required.
Design for
enhanced TP
removal. Use
ponds with
wetlands for
better TP
removal.
Design for
enhanced TP
removal. Use
ponds with
wetlands for
better TP
removal.
Moderate
bacteria
removal.
Good to
moderate TN
removal.
Provide
permanent
pools.
Infiltration 100' SD from
water supply
wells.
OK, but soils
overlaying
volcanic
dominated
regions may
limit
application.
OK, if site has
appropriate
soils.
OK, if site has
appropriate
soils.
OK, but
maintain 3' SD
from seasonal
high
groundwater.
Best TN
removal within
B soil horizon.
Filtering
Systems
OK, ideal
practice for
pretreatment
prior to
infiltration.
Practices
rarely
provide
quantity
control,
other BMP
needed.
OK, moderate
to high TP
removal.
OK, moderate
to high TP
removal.
OK, moderate
to high
bacteria and
nitrogen
removal.
Open Channels OK, pre-treat
100% WQv for
hotspots.
OK, should
be linked w/
basin for
quantity
control.
OK, Dry swale
provides the
best TP
removal.
OK, Dry swale
provides the
best TP
removal.
Poor bacteria
removal.
SD = separation distance
ED = extended detention
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3.5.4 Step 4 - Stormwater Management Capability
This matrix examines the capability of each BMP option to meet stormwater management
goals. It shows whether a BMP can provide for:
Water Quality Criteria. The matrix tells whether each practice can be used to provide water
quality treatment effectively. For more detail, consult the pollutant removal matrix, Matrix 5.
Recharge. The matrix indicates whether each practice can provide groundwater recharge.
Groundwater recharge is not a formal criteria but often a design goal to help replenish
groundwater supplies for drinking water and to augment freshwater stream flows.
Quantity Control. The matrix shows whether a BMP can typically meet flooding issues for
the site. Again, the finding that a particular BMP cannot meet these requirements does not
necessarily mean that it should be eliminated from consideration, but rather is a reminder that
more than one practice may be needed at a site (e.g., a bioretention area and a downstream
stormwater pond).
Table 3.19 BMP Selection Matrix 4-Stormwater Management Capability
BMP Group
BMP Design
Water
Quality?
Recharge?
Quantity
Control?
Ponds/ Wetlands Micropool ED | z |
ED Wetland | z |
Wet ED Pond | z |
Infiltration Infiltration
Trench/Chambers | | [
Filters Sand Filter | Y z
Organic Filter | Y z
Bioretention | Y z
Open Channels Dry Swale | Y z
Oversized Swale | Y z
Amended Grass
Channel Z Y z
| Practice generally meets this stormwater management goal.
z Practice can almost never be used to meet this goal.
X Since intercepting groundwater, side slopes contribute.
Y Provides recharge only if designed as an exfilter system.
Z Practice may partially meet this goal, or under specific site and design conditions.
[ Can be used to meet flood control in rare conditions, with very cobbly or highly
permeable soils.
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3.5.5 Step 5 - Pollutant Removal
This matrix examines the capability of each BMP option to remove specific pollutants
from stormwater runoff. The matrix includes data for:
• Total Suspended Solids
• Total Phosphorous
• Total Nitrogen
• Metals
• Bacteria
• Hydrocarbons
Table 3.20 BMP Selection Matrix 5-Pollutant Removal
Practice TSS
[%]
TP
[%]
TN
[%]
Metals1
[%]
Bacteria
[%]
Hydrocarbons
[%]
Wet Ponds/Wetlands 80 51 33 62 70 812
Filtering Practices 86 59 38 69 372 842
Infiltration Practices3 952 80 51 992 N/A5 N/A
Open Channels4 81 34 842 70 N/A 622
1. Average of zinc and copper. Only zinc for infiltration.
2. Based on fewer than five data points (i.e., independent monitoring studies).
3. Includes porous pavement, which is not on the list of approved practices for Hawaii.
4. Higher removal rates expected for dry swales.
5. While no data is available on the removal of bacteria for infiltration practices, it is generally
accepted that if there is a good soil matrix, removal is expected to be high; while if there is
little organic matter and a shallow soil profile over limestone, removal is likely to be poor.
N/A: Data not available
Removals represent median values from Winer (2000)
3.5.6 Step 6 - Community and Environmental
The last step assesses community and environmental factors involved in BMP selection.
This matrix employs a comparative index approach. An open circle indicates that the
BMP has a high benefit and a dark circle indicates that the particular BMP has a low
benefit.
Maintenance. This column assesses the relative maintenance effort needed for an BMP,
in terms of three criteria: frequency of scheduled maintenance, chronic maintenance
problems (such as clogging) and reported failure rates. It should be noted that all BMPs
require routine inspection and maintenance.
Affordability. The BMPs are ranked according to their relative construction cost per
impervious acre treated. These costs exclude design, land acquisition, and other costs.
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Community Acceptance. This column assesses community acceptance, as measured by
three factors: market and preference surveys, reported nuisance problems, and visual
orientation (i.e., is it prominently located or is it in a discrete underground location). It
should be noted that a low rank can often be improved by a better landscaping plan.
Safety. A comparative index that expresses the relative public safety of an BMP. An
open circle indicates a reasonably safe BMP, while a darkened circle indicates deep pools
may create potential public safety risks. The safety factor is included at this stage of the
screening process because liability and safety are of paramount concern in many
residential settings.
Habitat. BMPs are evaluated on their ability to provide wildlife or wetland habitat,
assuming that an effort is made to landscape them appropriately. Objective criteria
include size, water features, wetland features and vegetative cover of the BMP and its
buffer.
Table 3.21 BMP Selection Matrix 6-Community and Environmental
BMP Group BMP List
Ea
s
e
O
f
Ma
i
n
t
e
n
a
n
c
e
Af
f
o
r
d
a
b
i
l
i
t
y
Co
m
m
u
n
i
t
y
Ac
c
e
p
t
a
n
c
e
Sa
f
e
t
y
Ha
b
i
t
a
t
Micropool ED |
ED Wetland | Ponds/
Wetlands
Wet ED Pond | | | z |
Infiltration Infiltration
Trench/Chambers z | | z
Sand Filter z z | z
Organic Filter z | | z Filters
Bioretention |
Dry Swale | | z
Oversized Swale | | z Open Channels
Amended Grass Channel | | z
| High Medium z Low
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3.6 General Landscaping for all BMPS
Landscaping is a critical element to improve both the function and appearance of
stormwater best management practices (BMPs). This chapter provides landscaping
criteria and plant selection guidance for effective stormwater BMPs. It is organized as
follows:
The first section, 3.6.1, outlines general guidance that should be considered when
landscaping any stormwater practice, as well as a detailed plant list of native woody and
herbaceous species that can be used when preparing a stormwater planting plan. These
practices include:
• Stormwater ponds and wetlands
• Infiltration and sand filter practices
• Bioretention
• Open Channels
• Filter Strips and Buffers
In addition, specific guidelines are presented for landscaping bioretention areas.
In Section 3.6.2, key factors in selecting plant material for stormwater landscaping are
reviewed, including hardiness zones, physiographic regions, hydrologic zones, and
cultural factors.
Native Species
This workbook encourages the use of native plants in stormwater management facilities.
Native plants are defined as those species which evolved naturally to live in this region of
the world. Practically speaking, this refers to those species which lived on the islands
before recent human settlement. Many introduced species were weeds brought in by
accident; others were intentionally introduced and cultivated for use as food, medicinal
herbs, spices, dyes, fiber plants, and ornamentals.
Introduced species can often escape cultivation and begin reproducing in the wild. This is
significant ecologically because many introduced species out-compete indigenous species
and begin to replace them in the wild. Some introduced species are invasive, have few
predators, and can take over naturally occurring species at an alarming rate. By planting
native species in stormwater management facilities, we can help protect the natural
heritage of Hawaii and provide a legacy for future generations.
Native species also have distinct genetic advantages over non-native species for planting
in Hawaii. Because they have evolved to live here naturally, indigenous plants are best
suited for the local climate. This translates into greater survivorship when planted and
less replacement and maintenance during the life of a stormwater management facility.
Both of these attributes provide cost savings for the facility owner.
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Finally, people often plant exotic species for their ornamental value. While it is
important to have aesthetic stormwater management facilities for public acceptance and
the maintenance of property value, it is not necessary to introduce foreign species for this
purpose. Many native species are aesthetically pleasing and can be used as ornamentals.
When selecting ornamentals for stormwater management facilities, planting preference
should be given to native ornamentals.
3.6.1 General Landscaping Guidance for All Stormwater BMPs
• Do not plant trees and shrubs within 15 feet of the toe of slope of a dam.
• Do not plant trees or shrubs known to have long tap roots within the vicinity of the
earth dam or subsurface drainage facilities.
• Do not plant trees and shrubs within 15 feet of perforated pipes.
• Do not plant trees and shrubs within 25 feet of a hydraulic outlet control structure.
• Provide 15-foot clearance from a non-clogging, low-flow orifice.
• Herbaceous embankment plantings should be limited to 10 inches in height, to allow
visibility for the inspector who is looking for burrowing rodents that may compromise
the integrity of the embankment.
• Provide slope stabilization methods for slopes steeper than 2:1, such as planted
erosion control mats. Also, use seed mixes with quick germination rates in this area.
Augment temporary seeding measures with container crowns or root mats of more
permanent plant material.
• Utilize erosion control mats and fabrics to protect in channels that are subject to
frequent wash outs.
• Stabilize all water overflows with plant material that can withstand strong current
flows. Root material should be fibrous and substantial but lacking a tap root.
• Sod drainage channels subjected to high velocities that are not stabilized by erosion
control mats.
• Divert flows temporarily from seeded areas until stabilized.
• Check water tolerances of existing plant materials prior to inundation of area.
• Stabilize aquatic and safety benches with emergent wetland plants and wetland seed
mixes.
• Do not block maintenance access to structures with trees or shrubs.
• Avoid plantings that will require routine or intensive chemical applications (i.e. turf
area).
• Have soil tested to determine if there is a need for amendments.
• Select plants that can thrive with on-site soil with no additional amendments or a
minimum of amendments.
• Decrease the areas where turf is used. Use low-maintenance ground cover to absorb
run-off.
• Plant stream and edge of water buffers with trees, shrubs, ornamental grasses, and
herbaceous materials where possible, to stabilize banks and provide shade.
• Maintain and frame desirable views. Be careful not to block views at entrances, exits,
or difficult road curves. Screen or buffer unattractive views into the site.
• Use plants to prohibit pedestrian access to pools or steeper slopes that may be unsafe.
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• The designer should carefully consider the long-term vegetation management strategy
for the BMP, keeping in mind the “maintenance” legacy for the future owners. Keep
maintenance area open to allow future access for pond maintenance. Provide a
planting surface that can withstand the compaction of vehicles using maintenance
access roads. Make sure the facility maintenance agreement includes a maintenance
requirement of designed plant material.
• Provide Signage for:
o Stormwater Management Areas to help educate the public when possible.
o Wildflower/native grass areas, when possible, to designate limits of
mowing.
• Avoid the overuse of any plant materials.
• Preserve existing natural vegetation when possible.
It is often necessary to test the soil in which you are about to plant in order to determine
the following:
• pH; whether acid, neutral, or alkali
• major soil nutrients; Nitrogen, Phosphorus, Potassium
• minerals; such as chelated iron, lime
Have soil samples analyzed by experienced and qualified individuals, such as those at the
Pacific Basin Natural Resources Conservation Service (NRCS), who will explain in
writing the results, what they mean, as well as what soil amendments would be required.
Certain soil conditions, such as marine clays or volcanic soils, can present serious
constraints to the growth of plant materials and may require the involvement of qualified
professionals. When poor soils can’t be amended, seed mixes and plant material must be
selected to establish ground cover as quickly as possible.
Areas that have recently been involved in construction can become compacted so that
plant roots cannot penetrate the soil. Seeds lie on the surface of compacted soils,
allowing seeds to be washed away or be eaten by birds. Soils should be loosened to a
minimum depth of two inches, preferably to a four-inch depth. Hard soils may require
discing to a deeper depth. The soil should be loosened regardless of the ground cover.
This will improve seed contact with the soil, providing greater germination rates,
allowing the roots to penetrate into the soil. If the area is to be sodded, discing will allow
the roots to penetrate into the soil. Weak or patchy crops can be prevented by providing
good growing conditions.
Whenever possible, topsoil should be spread to a depth of four inches (two-inch
minimum) over the entire area to be planted. This provides organic matter and important
nutrients for the plant material. This also allows the stabilizing materials to become
established faster, while the roots are able to penetrate deeper and stabilize the soil,
making it less likely that the plants will wash out during a heavy storm.
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If topsoil has been stockpiled in deep mounds for a long period of time, it is desirable to
test the soil for pH as well as microbial activity. If the microbial activity has been
destroyed, it is necessary to inoculate the soil after application.
Remember that newly installed plant material requires water in order to recover from the
shock of being transplanted. Be sure that some source of water is provided, should dry
periods occur after the initial planting. This will reduce plant loss and provide the new
plant materials with a chance to establish root growth.
Bioretention - Planting Soil Bed Characteristics
The characteristics of the soil for the bioretention facility are perhaps as important as the
facility location, size, and treatment volume. The soil must be permeable enough to
allow runoff to filter through the media, while having characteristics suitable to promote
and sustain a robust vegetative cover crop. In addition, much of the nutrient pollutant
uptake (nitrogen and phosphorus) is accomplished through adsorption and microbial
activity within the soil profile. Therefore, the soils must balance soil chemistry and
physical properties to support biotic communities above and below ground.
The planting soil should be a sandy loam, loamy sand, loam (USDA), or a loam/sand mix
(should contain ~80% sand, by volume). The clay content for these soils should by less
than 5% by volume. Soils should fall within the SM, or ML classifications of the Unified
Soil Classification System (USCS). A permeability of at least 1.0 feet per day (0.5"/hr) is
required. The soil should be free of stones, stumps, roots, other woody material over 1"
in diameter, or brush/seeds from noxious weeds. Placement of the planting soil should be
in lifts of 12 to 18", loosely compacted (tamped lightly with a dozer or backhoe bucket).
The specific characteristics are presented in Table 3.22.
Table 3.22 Planting Soil Characteristics (Adapted from EQR, 1996; ETAB, 1993)
Parameter Value
PH range 5.2 to 7.00
Organic matter 1.5 to 4.0%
Magnesium 35 lbs. per acre, minimum
Phosphorus (P2O5) 75 lbs. per acre, minimum
Potassium (K2O) 85 lbs. per acre, minimum
Soluble salts 500 ppm
Clay* 0 to 5%
Silt* <15 to 20%
Sand* >50%
*Native soil characteristics. Augment native soils with aged leaf compost and acceptable topsoil
(see Section 3.4.2.3).
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Mulch Layer
The mulch layer plays an important role in the performance of the bioretention system
(surface layer varies based on design numbers 1-3). The mulch layer helps maintain soil
moisture and avoids surface sealing which reduces permeability. Mulch helps prevent
erosion, and provides a micro-environment suitable for soil biota at the mulch/soil
interface. Mulch also serves as a pretreatment layer, trapping the finer sediments which
remain suspended after the primary pretreatment.
The mulch for Bioretention Design No. 3 should be standard landscape style, single or
double, shredded tangantangan or coconut mulch or chips. The mulch layer should be
well aged (stockpiled or stored for at least six (6) months), uniform in color, and free of
other materials, such as weed seeds, soil, roots, etc. The mulch should be applied to a
maximum depth of three inches. Grass clippings should not be used as a mulch material.
Planting Plan Guidance
Plant material selection should be based on the goal of simulating a terrestrial forested
community of native species. Bioretention simulates an ecosystem consisting of an
upland-oriented community dominated by trees, but having a distinct community, or sub-
canopy, of understory trees, shrubs and herbaceous materials. The intent is to establish a
diverse, dense plant cover to treat stormwater runoff and withstand urban stresses from
insect and disease infestations, drought, temperature, wind, and exposure.
The proper selection and installation of plant materials is key to a successful system.
There are essentially three zones within a bioretention facility (Figure 3.13). The lowest
elevation supports plant species adapted to standing and fluctuating water levels. The
middle elevation supports a slightly drier group of plants, but still tolerates fluctuating
water levels. The outer edge is the highest elevation and generally supports plants
adapted to dryer conditions.
The layout of plant material should be flexible, but should follow the general principals
described in Table 3.23. Tree density of approximately one tree per 300 square feet (i.e.,
15 feet on center) is recommended. Shrubs and herbaceous vegetation should generally
be planted at higher densities (10 feet on center and 5 feet on center, respectively). The
objective is to have a system which resembles a random and natural plant layout, while
maintaining optimal conditions for plant establishment and growth.
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Figure 3.13 Planting Zones for Bioretention Facilities
Table 3.23 Planting Plan Design Considerations
Native plant species should be specified over exotic or foreign species.
Appropriate vegetation should be selected based on the zone of hydric tolerance
Species layout should generally be random and natural.
A canopy should be established with an understory of shrubs and herbaceous materials.
Woody vegetation should not be specified in the vicinity of inflow locations.
Trees should be planted primarily along the perimeter of the bioretention area.
Urban stressors (e.g., wind, sun, exposure, insect and disease infestation, drought)
should be considered when laying out the planting plan.
Noxious weeds should not be specified.
Aesthetics and visual characteristics should be a prime consideration.
Traffic and safety issues must be considered.
Existing and proposed utilities must be identified and considered.
Plant Material Guidance
Plant materials should conform to the American Standard Nursery Stock, published by
the American Association of Nurserymen, and should be selected from certified,
reputable nurseries. Planting specifications should be prepared by the designer and
should include a sequence of construction, a description of the contractor's
responsibilities, a planting schedule and installation specifications, initial maintenance,
and a warranty period and expectations of plant survival. Table 3.24 presents some
typical issues for planting specifications.
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Table 3.24 Planting Specification Issues for Bioretention Areas
Specification
Element Elements
Sequence of
Construction
Describe site preparation activities, soil amendments, etc.; address erosion
and sediment control procedures; specify step-by-step procedure for plant
installation through site clean-up.
Contractor's
Responsibilities
Specify the contractor’s responsibilities, such as watering, care of plant
material during transport, timeliness of installation, repairs due to
vandalism, etc.
Planting Schedule
and Specifications
Specify the materials to be installed, the type of materials (e.g., B&B, bare
root, containerized); time of year of installations, sequence of installation
of types of plants; fertilization, stabilization seeding, if required; watering
and general care.
Maintenance
Specify inspection periods; mulching frequency (annual mulching is most
common); removal and replacement of dead and diseased vegetation;
treatment of diseased trees; watering schedule after initial installation (once
per day for 14 days is common); repair/replacement of staking and wires.
Warranty Specify the warranty period, required survival rate, and expected condition
of plant species at end of warranty period.
3.6.2 Other Considerations in Stormwater BMP Landscaping
Use or Function
In selecting plants, consider their desired function in the landscape. Is the plant needed
as ground cover, soil stabilizer, or a source of shade? Will the plant be placed to frame a
view, create focus, or provide an accent? Does the adjacent use provide conflicts or
potential problems and require a barrier, screen, or buffer? Nearly every plant and plant
location should be provided to serve some function in addition to any aesthetic appeal.
Plant Characteristics
Certain plant characteristics are so obvious that they may actually be overlooked in the
plant selection. These are:
• Size
• Shape
For example, tree limbs, after several years, can grow into power lines. A wide-growing
shrub may block an important line of sight to oncoming vehicular traffic. A small tree
could strategically block the view from a second-story window. Consider how these
characteristics can work for you or against you, today and in the future.
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Other plant characteristics must be considered to determine whether the plant will fit with
the landscape today and through the years to come. Some of these characteristics are:
• Color
• Texture
• Aesthetic Interest, i.e.- Flowers, Fruit, Leaves, Stems/Bark
• Growth rate
In urban or suburban settings, residents living next to a stormwater system may desire
that the facility be appealing or interesting. Aesthetics is an important factor to consider
in the design of these systems. Failure to consider the aesthetic appeal of a facility to the
surrounding residents may result in reduced value to nearby lots. Careful attention to the
design and planting of a facility can result in maintained or increased values of a
property.
Availability and Cost
Often overlooked in plant selection is the availability from wholesalers and the cost of the
plant material. There are many plants listed in landscape books that are not readily
available from the nurseries. Without knowledge of what is available, time spent
researching and finding the one plant that meets all the needs will be wasted, if it is not
available from the growers. It may require shipping, therefore, making it more costly
than the budget may allow. Some planting requirements may require a special effort to
find the specific plant that fulfills the needs of the site and the function of the plant in the
landscape.
3.7 Case Studies
This section provides two case studies to illustrate the techniques presented in this
Chapter. The first case study steps through the BMP selection process for a commercial
site on Maui. The second case study shows how to determine the required treatment
volume for a residential development on Kauai.
3.7.1 BMP Selection Example
The Honu Beach Shopping Center is a hypothetical commercial development located in
Kihei, Maui. The 5-acre shopping center consists of many different businesses, which
ultimately connect to an existing storm drain discharging to a nearby coastal area.
Instead of trying to direct all the runoff from the site to one treatment facility, it is more
effective to divide the area into subcatchments based on localized topography/grading
and use. This example focuses on a bank, with a site area of 0.5 acres and 80%
impervious cover (see Figure 3.14), with fill soils classified as “Urban Land” and 10 feet
to groundwater. Using the site characteristics and the BMP selection matrices from
Section 3.5, we will choose appropriate BMP(s) for this area.
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BMP Selection Process
In order to select a treatment BMP for this site, we need to consider site constraints based
on the categories presented in Section 3.5, as follows:
• Land Use
• Physical Feasibility
• Watershed
• Stormwater Management Capability
• Pollutant Removal
• Community and Environmental
Land Use: The site consists of mostly a parking lot and the building, with a few scattered
landscaped areas. It is a commercial land use, but not a hotspot. Based on the Selection
Matrix 1, the best BMPs are infiltration or filtering practices.
Physical Feasibility: The small area of our site is a physical constraint – there is not
enough room to have a stormwater pond or wetland. The fill soils are fine for filtering
and open channel practices.
Watershed: Our site discharges ultimately to coastal waters, for which the best practices
are infiltration and filtering BMPs.
Stormwater Management Capability: All the BMPs are appropriate for treating the water
quality volume – no constraints for this category.
Pollutant Removal: The main pollutant
of concern for a parking lot is sediment
and hydrocarbons from cars. The best
practices for both of these are filtering
practices.
Community and Environmental: From
the previous matrices, we know that
filtering practices are the best fit for our
site. Using BMP Selection Matrix 6,
bioretention systems are the most
affordable of the filtering practices. In
addition, bioretention areas can be
planted with aesthetically pleasing
plants and have low public safety risks.
Final BMP Design
The best BMP for use at our site is a
bioretention area. Bioretention is a great
way to provide treatment for parking lots Figure 3.14 BMP Selection at the Honu
Beach Shopping Center
LID WORKBOOK: A PRACTITIONER’S GUIDE
3-76
because landscaped parking lot islands can easily be designed/converted to accept
stormwater. Bioretention can be on-line or off-line facilities. In this case, due to the
small size of the site, it can be designed to accept surface runoff from the parking lot (on-
line), with a grass filter strip for pretreatment. An overflow is provided to convey flow
from larger storms into the closed system.
In addition, there are ways to incorporate more low-impact techniques at this site.
Rooftop runoff could be collected and used to water the landscaping. Permeable pavers
could be used for the overflow parking or parking spaces could be reduced based on the
need at the site.
3.7.2 Treatment Volume Calculation
Aloha Estates is a hypothetical medium-density residential development located in
Kapa’a, Kauai (Figure 3.15). It consists of approximately 180 ¼-acre lots, with
approximately 28,000 linear feet of 48-ft wide residential roads. The development covers
44 acres, with 30 acres of impervious surfaces (roads, driveways, sidewalks, and
rooftops. The annual rainfall for its location is approximately 50 inches/year. The
following steps can be used to determine the WQv, as described in Section 3.3:
1. Define Site Area and
Impervious Cover
The total site area is 44 acres.
The impervious cover percentage
is 30 acres/44 acres = 68%.
2. Compute Runoff Coefficient
for Site
The volumetric runoff coefficient
is defined based on the following
equation:
Rv = 0.05 + 0.009 (I) =
0.05 + 0.009 (0.68) = 0.056
3. Determine Appropriate Water
Quality Storm (S)
Our site has an annual rainfall of
50 inches/year, which falls into
the Zone No. 2 category from
Table 3.2 in Section 3.3). The
appropriate water quality storm
depth for this site is S = 1.0 inch.
Figure 3.15 Hypothetical Medium-density
Residential Development - Aloha Estates
LID WORKBOOK: A PRACTITIONER’S GUIDE
3-77
4. Compute Water Quality Volume (WQv)
The WQv expresses the cubic feet of runoff that must be treated in an acceptable
stormwater treatment practice, and is computed as:
WQv = (Rv) (S) (A) (3,630) = (0.056) (1.0) (44 ac) (3,630) = 8,944 cf
Where = A = total site area, in acres
5. Select Appropriate Best Management Practice (BMP)
The final step is to select appropriate BMPs to treat the WQv. For this project, the
designer chose to utilize dry swales, an infiltration basin, and a wet pond to treat
stormwater runoff. LID techniques could be used to reduce the WQv required, such as
using permeable pavers for the sidewalks and driveways, directly infiltrating roof runoff
or capturing it in rain barrels, reducing road widths, changing the pattern of development
to reduce cul de sacs, and using rain gardens in the center of the cul de sacs.
LID WORKBOOK: A PRACTITIONER’S GUIDE
3-78
3.8 References
Atlanta Regional Commission. August 2001. Georgia Stormwater Management Manual.
Atlanta, GA. Available from www.georgiastormwater.com.
Bannerman, R. T., Owens, D. W. Dodds, R. B. and N. J. Hornewer. 1993. Sources of
pollutants in Wisconsin stormwater. Water Science and Technology 28(3-5): 241-59.
Center for Watershed Protection. April 2002. The Vermont Stormwater Management
Manual. Vermont Agency of Natural Resources, Waterbury, VT. Available from
www.vtwaterquality.org/stormwater.htm.
City of Austin. 1988. Water Quality Management. In Environmental Criteria Manual.
Environmental and Conservation Services. Austin, TX.
Claytor, R. and T. Schueler. 1996. Design of Stormwater Filtering Systems. Center for
Watershed Protection. Ellicott City, MD.
Fukuda, K., P. Lui, W. Okazaki, K. Pacheco, and N. Sultana. 2004. Impervious Cover
Analysis and Study of Existing Regulation vis-à-vis Low Impact Design for the State
of Hawai’i, Prepared for Hawai’i Office of Planning, Honolulu, Hawai’i. Department
of Urban and Regional Planning, University of Hawai’i, Honolulu.
Galli, F.J. 1990. Peat-sand filters: a proposed stormwater management practice for urban
areas. Dept. of Environmental Programs. Metropolitan Washington Council of
Governments. Washington, DC.
Hollis, G. E. 1975. The effect of urbanization on floods of different recurrence interval.
Water Resources Research 11(3):431-435.
Leopold, L. B. 1994. A View of a River. Harvard University Press. Cambridge, MA.
Oki, D.S. 2003. Surface Water in Hawaii - USGS Fact Sheet 045-03. Prepared in
cooperation with the State of Hawaii Commission on Water Resource Management.
Schueler, T.R. 1987. Controlling Urban Runoff: A Practical Manual for Planning and
Designing Urban BMPs, Department of Environmental Programs, Metropolitan
Washington Council of Governments, Washington, DC.
Schueler, T.R. 1994. The Importance of Imperviousness. Watershed Protection Techniques.
1(3): 100-111.
Schueler, T.R. 2006. Design Guidelines for Stormwater Treatment Practices to Protect
Water Quality in Maui County, Hawaii, Prepared for Department of Public Works
and Environmental Management, Wailuku, Hawaii.
LID WORKBOOK: A PRACTITIONER’S GUIDE
3-79
Steuer, J., W. Selbig, N. Hornewer, and J. Prey. 1997. Sources of Contamination in an Urban
Basin in Marquette, Michigan and an Analysis of Concentrations, Loads, and Data
Quality. U.S. Geological Survey, Water-Resources Investigations Report 97-4242.
Trimble, S. W. 1997. Contribution of stream channel erosion to sediment yield from an
urbanizing watershed. Science 278:1442-1444.
USEPA. 2005. National Menu of Best Management Practices for Stormwater Phase II.
http://cfpub.epa.gov/npdes/stormwater/menuofbmps/menu.cfm.
Waschbusch et al. 2000. Sources of phosphorus in stormwater and street dirt from two urban
residential basins in Madison, Wisconsin, 1994-1995. In: National Conference on
Tools for Urban Water Resource Management and Protection. US EPA February
2000: pp. 15-55.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-1
4
Wastewater management is an important component of watershed protection. Wastewater
discharges can affect drinking water supplies, fresh water systems and coastal resources.
Wastewater throughout Hawaii and the rest of the country is managed through a variety of onsite
systems, clustered or small wastewater treatment facilities, or larger, centralized wastewater
treatment plants. Hawaii Administrative Rules, Title 11, Department of Health, Chapter 62,
Wastewater Systems govern the disposal and treatment of wastewater in Hawaii (this rule will be
summarized below).
The goal of this chapter is to identify how onsite, cluster and centralized wastewater systems
function and describe how wastewater affects groundwater and surface water quality, focusing
on impacts from nitrogen, phosphorus, and pathogens discharged in wastewater effl uent. This
description is followed by a discussion of alternative technologies for wastewater treatment
and disposal that can be used to mitigate water quality issues with effl uent disposal. The
technologies described here are a sampling of those available for onsite systems and small
wastewater treatment facilities, and references and web links are provided for additional
information. Included in this discussion is a brief description of wastewater reuse, including the
use of treated effl uent for agricultural fi elds, landscaped areas and golf courses which is quite
common in Hawaii.
Finally, opportunities for protecting water quality through wastewater management are described.
A series of management approaches are identifi ed, highlighting innovative wastewater solutions
that focus on cluster development or “smart growth” village center areas. In addition, case
studies are provided that highlight both the uses of alternative technologies, as well as innovative
management approaches.
Regulatory Overview
(Excerpted from the National Small Flows Clearinghouse National Summary Citations
accessible at http://www.nesc.wvu.edu/nsfc/nsfc_national_summaries_1.htm)
Through Chapter 11-62, the Hawaii Department of Health (DOH) seeks to ensure that the use
and disposal of wastewater and wastewater sludge does not contaminate or pollute any valuable
water resource, does not give rise to public nuisance, and does not become a hazard or potential
hazard to the public health, safety and welfare. The DOH also ultimately hopes to ultimately
institute regional sewage collection, treatment and disposal systems which are consistent
with state and county wastewater planning policies. Off-site treatment and disposal systems,
followed in priority by onsite systems, meeting health and environmental standards will be
allowed whenever they are consistent with state and county wastewater planning policies and on
the premise that these systems will eventually connect to regional sewage systems. Individual
wastewater systems may be utilized in remote areas and in areas of low density. Chapter 11-62
applies statewide and can become more stringent on the local level if approved by the state.
Wastewater Management
4.1 Introduction
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-2
Chapter 11-62 also gives the mayor of each county the ability to ask the Director of the DOH
to form a county wastewater advisory committee to review and make recommendations to the
director on the application of Chapter 11-62 on matters which are unique to each county, on
the establishment of critical wastewater disposal areas, on proposals which are not specifi cally
addressed by Chapter 11-62, and upon the Director’s request, for applications for variances.
Critical wastewater disposal areas may be established by the Director in each county based on
concerns relating to a high water table, impermeable soil or rock formations, steep terrain, fl ood
zone, protection of coastal waters and inland surface waters, high rate of cesspool failures, and
protection of groundwater resources.
4.2 Approved Wastewater Treatment Technologies
Wastewater Treatment Technologies Approved for use in Hawaii include:
• Conventional - Aerobic treatment units, septic tanks, soil absorption beds and trenches,
absorption or seepage pits, dry wells, sand fi lters, mounds, and evapotranspiration beds.
• Alternative - Gravelless chambers, some gravelless pipe systems, constructed wetlands,
composting and incineration toilets, and aerobic systems with NSF Standard 40 certifi cation.
• Experimental - Each installation requires local Board of Health approval and dedicated
site for replacement with conventional or alternative systems. No specifi c products or
technologies are identifi ed as experimental, but an experimental technology can be approved
on a case-by-case basis.
Provisions exist for the Director of Health to allow other innovative and alternative technologies.
The DOH allows the technology to be used on an experimental basis during which performance
data are gathered over a period to demonstrate that the technology functions as described.
All site evaluations and wastewater system design are required to be done by a professional
engineer licensed in Hawaii. A percolation test or soil characterization is required as part of
the site evaluation. There is a minimum lot size of 10,000 square feet for the use of an onsite
wastewater system in Hawaii. Minimum setback/separation distances include:
On December 9, 2004, a number of amendments to Chapter 11-62 were signed into law by the
Governor. Major changes include:
• Establishes criteria for wastewater sludge (biosolids) to be used or disposed;
• Requires wastewater treatment facilities to obtain either an individual wastewater permit or
coverage under the general permit for treatment works;
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-3
• Requires cesspool pumpers and grease trap haulers to be registered with the Department of
Health;
• The Department’s Reuse Guidelines and Animal Waste Guidelines are referenced in the rule;
• Establishes effl uent quality for recycled water systems and incorporates the Department’s
Spill Protocol into the rules;
• Revises many requirements for individual wastewater systems;
• Requires that septic tanks used in Hawaii meet the standards set by the International
Association of Plumbing and Mechanical Offi cials (IAPMO);
• Adds processing fees to applications for new and modifi ed individual wastewater systems;
and
• Allows the Department to issue fi eld citations for specifi c types of wastewater violations.
It should be noted that Hawaii still allows large capacity cesspools (LCCs) to be designed,
constructed and utilized in some wastewater disposal settings. However, in 2000 the U.S. EPA
banned the construction and use of new LCCs. Furthermore, as of 2005, the EPA mandated
that all existing LCCs be either upgraded or closed. A cesspool is considered to be a LCC if it
receives sanitary waste from multiple dwellings (such as a duplex) or receives waste from 20 or
more persons per day from a non-residential building. Cesspools serving single family homes
are not affected by this EPA ruling.
In Hawaii, Chapter 11-62 allows cesspools to serve duplexes and non-residential buildings that
may be used by 20 or more persons per day. Although these uses do not violate the provisions
of Chapter 11-62, they do violate U.S. EPA regulations and may result in fi nes of up to $32,500
per day for the owner of a LCC. It is possible to have a cesspool approved by the DOH that may
result in federal fi nes for its owner. DOH will notify building permit applicants proposing to
use a LCC of the potential federal rule violation and recommend that the wastewater system be
revised.
4.2.1 Septic Systems/Wastewater Treatment Facilities
Figure 4-1. Septic systems are comprised of a septic tank and a leaching facility .
Wetland
SepticTank LeachingFieldDistributionBox
WaterTable
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-4
The septic tank provides for the settling out of solids and some biological treatment of the
wastes. The leaching facility disposes of the liquid wastes into the subsurface environment.
Cesspools are essentially either a covered hole or pit for receiving drainage or sewage, as from a
house. There is no septic tank, and the settling of solids and the disposal of liquid wastes occurs
in the same place. As no biological treatment of wastes occurs as in a septic tank, a cesspool is
the least protective method of wastewater disposal (other than direct discharge of sewage onto
the ground or in a water body, which is illegal throughout the United States).
If septic tanks are not properly maintained (pumping once every three years is recommended
for single family homes), solids may pass out of the tank and clog the leaching facility. This can
cause hydraulic failure of the system resulting in the possible backing up of wastewaters into the
building or effl uent breaking out onto the land surface. The latter case often offers a direct route
of transport to a freshwater resource.
Conventional septic systems are designed to control pathogenic bacteria and are less effective
in treating other potential pollutants. Leaching facility effl uents contain approximately 40 to 60
mg/l nitrogen and 8-38 mg/liter phosphorus (Hall, 1975). Nitrogen compounds generally move
through the groundwater system relatively intact, ultimately reaching water bodies. Viruses,
being much smaller than bacteria, also move easily through soils at the speed of groundwater.
Because their inactivation times in groundwater are approximately 120-200 days, they have
been documented to move distances greater than 300 feet in soils. If a septic system is located
too close to a water body, viruses may reach surface waters. Septic systems sometimes introduce
hazardous wastes into the groundwater if the owner uses septic cleaners or improperly disposes
of household hazardous wastes.
The cumulative effects of many single family septic systems on nutrient, pathogen, or hazardous
waste levels in down-gradient waters can be very signifi cant. These impacts are dependent upon
septic system location and density relative to receiving water bodies.
Wastewater treatment facilities are a source of direct discharges to water bodies. In some cases
in the southwestern United States, these water discharges are the main source of water within the
streams. Although partially treated, these discharges can still contain materials such as metals
and other organics not treated in the wastewater treatment facility.
Onsite Septic Systems Impacts to Water Quality Onsite Septic Systems Impacts to Water Quality
Onsite septic systems typically consist of a septic tank and a leaching or disposal facility (Figure
5-1). Wastewater that fl ows through the system and reaches the underlying aquifer still contains
dissolved materials such as salts, nutrients, solvents, toxic compounds, metals, and soluble
pesticides. This wastewater also still contains pathogens such as bacteria and viruses and some
very small particles of insoluble materials. Water quality concerns associated with the primary
constituents of septic system effl uent are described below.
NitrogenNitrogen: Nitrogen in septic system effl uent is present in concentrations well above the 10-mg/
L federal drinking water standard. Effl uent from a properly operating septic system typically
contains 40 milligrams per liter (mg/L) nitrogen (H&W, Inc., 1998). This is four times higher
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-5
than the Drinking Water Standard. If one is drinking water from a private well that contains
nitrogen at or near the 10-mg/L standard, it is possible the water contains approximately 25%
recycled wastewater effl uent. Elevated levels of nitrate in drinking water can cause serious
problems for infants, who could develop methaglobamenia (Blue Baby Syndrome), if the water
is used in the preparation of formula or drinking water. It is, at elevated levels, a potential
concern for adults as a carcinogen (Weyer, et al., 2001). Nitrate-nitrogen in septic system
effl uent does not precipitate or sorb to the soil materials through which it travels in groundwater
and further attenuation is only caused by mixing and dilution with native groundwater. The
effl uent travels as a plume as it leaves the septic system, and the mixing only occurs as it either
reaches a surface water (such as the coast) or is withdrawn through a pumping well.
Excessive nitrogen has been found to accelerate eutrophication in some coastal and estuarine
waters (Wetzel, 1983). The critical concentration for marine waters can be as low as 0.2 mg/l,
depending on the rate of tidal fl ushing (Nielson, 1981; Buzzards Bay Project, 1991). Excessive
nitrogen loading to marine and brackish ecosystems can cause algal blooms, decreased water
clarity, and declines in eelgrass beds which are important shellfi sh and fi nfi sh habitat.
PhosphorusPhosphorus: Phosphorus concentrations in typical septic system effl uent are far in excess of
acceptable levels for surface water bodies and are known to be major causes of algal blooms and
eutrophic conditions in ponds, lakes and streams. Unlike nitrogen, phosphorus reacts with, or is
sorbed to, sediments and rock particles in the ground and initially does not travel more than a
few feet from a septic system leaching facility. However, after years of application, the reactants
and sorptive capacity of sand and gravel soils becomes exhausted. Phosphorus will gradually
be transported further and further form the septic system, ultimately to a discharge point in a
wetland or surface water (such as pond or the ocean).
Bacteria and Viruses: Pathogenic microorganisms (bacteria and viruses) are also found in
domestic wastewater. In a properly operating septic system, the effl uent does not discharge
on land surface and the potential for human contact and infection from bacteria is low. The
movement and survival of bacterial contaminants in the groundwater has been studied
extensively. It has been shown that most bacteria are attenuated within a short distance of the
point where they leave the leaching facility; usually between one to thirty metres in permeable
sands and gravel (Canter and Knox, 1986). Bacteria are attenuated by adsorption to solid soil
and aquifer materials and by death in slow-moving groundwater. In malfunctioning systems,
pathogenic organisms can be discharged to the surface and contaminate soil and surface waters.
Research (Yates, 1987) indicates that viruses from septic system effl uent can persist over longer
periods of time in groundwater than in surface water, and the transport of viruses in groundwater
occurs over longer distances and over longer periods of time than does the transport of bacteria.
Viruses are ultramicroscopic particles, ranging from about 20 to 200 nanometres in diameter
of a host cell. Only infected individuals can introduce them to septic system effl uent. Unlike
bacteria, they do not require nutrients in groundwater to survive and, therefore, can persist in
groundwater for longer periods than bacteria.
Attenuation of viruses in groundwater is dependent on time and groundwater temperature. The
colder the groundwater, the longer the viruses will survive. The longer the viruses are in the
ground, the more they die off, until they eventually become inactive and no longer a health
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-6
threat. In order to determine how far viruses may travel in the ground, the inactivation rate for
virus in groundwater is compared to the rate of groundwater fl ow. The overall extent of travel
will also be infl uenced by the height of the leaching facility above the water table, as viruses will
be attenuated in this zone before they reach the aquifer. See Chapter 3 for more detail.
4.3 Alternative Onsite Wastewater Technologies
An alternative onsite system is an onsite treatment system other than a conventional septic tank
and leach fi eld design. Alternative systems are used to accommodate a variety of site conditions
(e.g., high ground water, low-permeability soil) and/or to provide additional treatment.
Sometimes systems are classifi ed as alternative because, even though they make use of a
conventional septic tank and leach fi eld, they also utilize an alternative plumbing fi xture such as
a composting toilet. Other examples of alternative wastewater technologies include recirculating
sand fi lters, intermittent sand fi lters, trickling fi lters, sequencing batch reactors, aerobic treatment
units and nitrate reactive media.
The same alternative treatment technologies used in onsite systems can be scaled up for use in
cluster or centralized or community systems.
The information that follows is not an exhaustive
listing of all the alternative wastewater
technologies available.
Composting ToiletsComposting Toilets (excerpted from U.S.
EPA’s Water Effi ciency Technology Fact Sheet
– Composting Toilets, 1999)
Composting toilets have been an established
technology for more than 30 years and
they require little to no water, enabling
them to provide a solution to sanitation and
environmental problems in unsewered, rural
and suburban areas. The system relies on
unsaturated conditions where aerobic bacteria
break down waste. The resulting “humus”
must be disposed of either through burial or
removal by a licensed septage hauler. A typical
composting toilet is a well-ventilated container
that collects and composts waste (including
toilet paper) in a large container installed
below the toilet in a basement or in a small
compartment located directly beneath the toilet.
Composting toilets can be used almost anywhere
a fl ush toilet can be used, but typically appear
in seasonal homes, homes in remote areas and
recreation areas. Some examples of composting
toilets include the Clivis Multrum, the Biolet and
the Carousel to name a few.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-7
Recirculating Sand FiltersRecirculating Sand Filters (excerpted from U.S. EPA’s Decentralized Systems Technology Fact
Sheet – Recirculating Sand Filters, 1999)
A recirculating sand fi lter (RSF) is a modifi ed version of a single-pass open sand fi lter. It was
designed to alleviate odor problems associated with open sand fi lters through recirculation,
which increases the oxygen content in the effl uent distributed on the fi lter bed. RSFs can be used
on sites that have shallow soil cover, inadequate permeability, high groundwater and limited land
area. The most important treatment process in a RSF is a biological one, and RSFs typically
produce a high quality effl uent with about 85% to 95% biological oxygen demand (BOD) and
total suspended solids (TSS) removal. In addition, RSFs may also remove up to 50% of nitrogen
within the treated effl uent. RSFs are typically found serving subdivisions, mobile home parks,
rural schools, small municipalities and other small wastewater generators such as individual
family residences. Some manufacturers of RSFs include Ashco, American Manufacturing
Company and others.
Intermittent Sand Filters (excerpted from U.S. EPA’s Wastewater Technology Fact Sheet
– Intermittent Sand Filters, 1999)
Intermittent Sand Filters (ISFs) have 24-inch deep fi lter beds of carefully graded media (typically
sand but not always). The surface of the bed is intermittently dosed with effl uent that percolates
in a single pass through the sands to the bottom of the fi lter. After being collected from the
underdrain, the treated effl uent is transported to a line for further treatment or disposal. ISFs
are typically built below grade in excavations 3 to 4 feet deep and lined with an impermeable
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-8
membrane where required. Discharges from ISFs are usually of high quality and can be used
for drip irrigation or for surface discharge after disinfection. Typical concentrations of BOD
and TSS are 5 milligrams per liter or less and nitrifi cation of 80% or more of applied ammonia
is usually achieved. ISFs serve the same users as RSFs, and manufacturers include Orenco
Systems, Inc., Infi ltrator Systems, Inc. and others.
Trickling FiltersTrickling Filters (excerpted from U.S. EPA’s Onsite Wastewater Treatment Systems Technology
Fact Sheet 2 – Fixed Film Processes, 2002 and Decentralized Systems Technology Fact Sheet
– Types of Filters, 2000 as well as information from the Caribbean Environment Programme
Technical Report #43, 1998 accessed at http://www.cep.unep.org/pubs/Techreports/tr43en/
Low%20cost.htm)
Trickling fi lters are one form of fi xed fi lm systems. Fixed fi lm systems are biological treatment
processes that employ a medium (such as peat) that will support a biomass on its surface and
within its porous structure. Other fi lter media include foam, crushed glass and textile chips. In
a trickling fi lter, the medium is held in place and is stationary relative to the wastewater fl ow.
Much research has been conducted on peat in the northeastern United States, where peat is
readily available. Peat fi lters used for onsite wastewater treatment remove about 60% to 90%
of BOD, but no long term data are available. As peat is a natural material, signifi cant variations
in composition can occur. Several manufacturers of peat trickling fi lters enclose the peat in
fi berglass housing or polyethylene modules. Peat (and other media) trickling fi lters have been
installed at single and multiple family residential dwellings, elementary and high schools,
commercial retail establishments and restaurants. Manufacturers include fi rms such as Oliver,
Mangione, McCalla & Associates in Canada, Bioclere, Waterloo Biofi lter System, Inc. and
others.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-9
Sequencing Batch ReactorsSequencing Batch Reactors (excerpted from U.S. EPA’s Wastewater Technology Fact Sheet
– Sequencing Batch Reactors, 1999)
The sequencing batch reactor (SBR) is a fi ll-and-draw activated sludge system for wastewater
treatment. In this system, wastewater is added to a single “batch” reactor, treated to remove
undesirable components and then discharged. To optimize performance, two or more batch
reactors are used in a predetermined sequence of operations. An advantage of this system is
its ability to manage and treat low or intermittent wastewater fl ows. In essence, the SBR is an
activated sludge system that operates in time rather than place. SBRs can achieve good BOD
and nutrient removal, with a BOD removal effi ciency of approximately 85% to 95%. Total
nitrogen can be reduced to as low as 5-8 milligrams per liter. SBRs are in use at condominiums,
mobile home parks, shopping centers, marinas, golf courses, resorts, campgrounds, motels,
restaurants, apartment buildings, small municipalities and neighborhoods, and can be scaled for
either small or large applications. Manufacturers include the Walden Corporation, Cromaglass,
Amphidrome and others.
Aerobic Treatment Units (excerpted from U.S. EPA’s Decentralized Systems Technology Fact
Sheet – Aerobic Treatment, 2000)
Aerobic treatment units provide a suitable oxygen rich environment for organisms that can
reduce the organic portion of the waste into carbon dioxide and water in the presence of
oxygen. Aerobic systems are similar to septic systems except that the treatment process requires
oxygen, therefore the units use a mechanism to inject and circulate air inside the treatment
tank. These mechanisms include diffused air, sparged turbine, or a surface entrainment
device. Two aerobic primary treatment systems have been adapted for onsite use: suspended
growth, where microorganisms are suspended within the waste stream, and fi xed fi lm, where
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-10
the microorganisms are attached to an inert medium within the waste stream. Suspended
growth units can provide for a 70% to 90% BOD reduction in household wastewater. Aerobic
treatment units are suited for use in single family dwellings, clustered subdivisions, restaurants
and other commercial applications as well as renovation of biologically failed septic systems.
Manufacturers include Bio-Microbics, Inc. and Smith & Loveless, Inc. (FAST systems), Jet, Inc.,
Norweco, Inc. and others.
Nitrate Reactive Media (NITREXNitrate Reactive Media (NITREXTM)) (excerpted from the U.S. EPA Region 1 website accessed
at http://www.epa.gov/NE/assistance/ceit_iti/tech_cos/waterloo.html))
In this system, a nitrate-reactive media (such as wood chips) converts nitrate to inert nitrogen gas
(denitrifi cation). The NITREXTM reactive media is contained in a prefabricated tank, or for larger
installations in an engineered excavation. Nitrate contaminated wastewater is gravitationally
fed through the treatment module. For septic tank applications, an oxidative pre-treatment
step is required to fi rst convert ammonium (NH4+) to nitrate (NO3-), then the NITREXTM
fi lter performs the reductive denitrifi cation step. Pre-treatment can be achieved with any of the
existing oxidative technologies, for example sand fi lters, commonly used in septic tank treatment.
The nitrate-free effl uent from the NITREXTM fi lter is simply discharged to a conventional tile
bed. The NITREXTM fi lter is passive and essentially maintenance free. It reportedly provides
almost 100% nitrate removal in a low cost, easy-to-install process. Manufacturers include
Wastewater Science, Inc. in Canada and Lombardo Associates, Inc. in the United States.
4.4 Clustered Wastewater Systems
A clustered wastewater system is a collection and treatment system under some form of common
ownership that collects wastewater from two or more dwellings or buildings and conveys it
to a treatment and disposal system located on a suitable site near the dwellings or buildings.
These systems can serve a small subdivision, an apartment building, a senior living complex,
or condominium units. Clustered wastewater systems can be very useful for rural servicing, as
they can allow for denser, village development to be maintained by collecting wastewater for
treatment and disposal away from private water wells or a community well. Clustered systems
also allow a community fl exibility in providing wastewater treatment and disposal services based
on facility use (e.g., offi ce complex or single family homes?) and facility location (e.g., within a
critical wastewater disposal area or outside of a critical wastewater disposal area?).
Therefore, it is entirely possible that several clustered systems or a combination of onsite and
clustered systems may be best to meet a community’s wastewater treatment and disposal needs.
The advantages gained by using clustered systems versus onsite systems include greater control
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-11
over maintenance of the system and therefore wastewater treatment, an enhanced ability to
prevent cross-connections between wastewater treatment systems and private or community
wells, and the ability to have multiple wastewater solutions within a community based on its
unique geographic and development characteristics. Administrative costs to a community can
also be reduced as clustered systems are typically privately maintained through a homeowners or
condominium association or by a corporate entity with DOH oversight.
Cluster systems offer a number of options in terms of collection, pretreatment, fi nal soil
absorption, and management of the system. Several types of alternative sewer systems such
as pressure, small diameter gravity, and vacuum sewers can be used to collect and transport
wastewater. Pressurized alternative sewer designs are appropriate for hilly or extremely fl at
terrain, shallow bedrock, high water table, or anywhere the costs and environmental impact of
excavating for traditional gravity sewers would be prohibitively expensive. Pressure sewers are
subdivided into grinder-pump systems, which shred sewage solids at each individual connection
prior to pumping the waste into the collection system, and septic tank effl uent pumping (STEP)
systems, which use septic tanks located at each connection to remove grit, grease and settleable
solids prior to pumping into the collection system.
Small-diameter gravity sewer systems are another alternative sewer option for small
communities. These systems use gravity, rather than pumps or pressure, to collect and transport
wastewater to a facility for treatment. Like STEP systems, septic tanks at each individual
connection remove most of the solids from the wastewater so the sewers transport relatively
solids-free effl uent. Vacuum sewers rely on suction, created at a central pumping station and
maintained in the small diameter mains, to draw and transport wastewater through the system to
fi nal treatment. When wastewater in a small holding tank at each connection reaches a certain
level, a sensor opens a pneumatic valve and the tank’s contents are sucked into the line by the
vacuum. Vacuum sewers are best suited for areas with fl at or gently rolling terrain, as they can
usually only transport waste about 20 feet uphill.
The pretreatment facility in a cluster system is often a larger version of ones found in some
individual onsite systems, such as aeration, constructed wetlands, or media fi lters, followed by
disposal of the treated effl uent into a soil absorption system. Some cluster systems empty into
a conventional sewer main that leads to a centralized municipal treatment facility. This may be
very cost effective for communities that have this option. There are also other disposal options.
If a proper site and soil area can be located nearby (such as a community park or facility such as
a baseball fi eld), it may be practical to dispose of treated sewage in a larger subsurface leachfi eld
or drainfi eld similar to the smaller ones used for individual homes or businesses with onsite
septic systems. Another disposal option may be drip irrigation, which places small amounts of
treated wastewater effl uent a few inches below ground surface where nutrients can be taken up
by the plants in the lawn or ball fi eld rather than leaching into groundwater.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-12
4.5 Centralized Wastewater Systems
A centralized wastewater system is a managed system consisting of collection sewers and
a single treatment plant used to collect and treat wastewater from an entire service area.
Traditionally, such a system has been called a publicly owned treatment works (POTW). In
many cases, these larger municipal systems transport sewage away from homes and businesses in
large diameter gravity sewers to a central plant where it is treated and eventually discharged into
a waterway. A centralized wastewater system is a good wastewater solution in larger densely
populated areas, since the cost of a municipal sewage system is lower if it can be distributed
over a larger number of users. However, centralized treatment systems operated by small
communities can perform poorly because of a lack of expertise and funding to maintain and
update the facility. Sewered small communities which treat and discharge wastewater account
for most of the non-compliance violations, according to the U.S. EPA.
When maintained properly, centralized wastewater systems can offer high levels of public health
and environmental protection. Centralized systems are also excellent in terms of supporting
high-density, village centers, as wastewater from these centers can be transported elsewhere
for treatment and disposal. In addition, a properly maintained centralized system virtually
eliminates the possibility of cross-connections between wastewater treatment and private or
community drinking water wells as the single discharge point can be optimally located away and
downgradient of drinking water sources.
4.6 Wastewater Reuse
(Excerpted from information provided by the Hawaii Water Environment Federation web site
accessed at http://www.hwea.org/wtrreuse.htm))m)m
In Hawaii and around the United States, population growth and development pressures are
straining the fresh water resources of many communities. To combat water shortages, more and
more communities and states are investigating wastewater reuse or recycling. In Hawaii, there
are three classifi cations of recycled water based on regulatory defi nitions (§11-62-03 and §11-62-
27). The classifi cations indicate levels of purity and determine how the water is monitored. The
water is not recycled if it does not meet the required level of quality.
R-1 is the highest quality recycled water. This water has gone through fi ltration and disinfection
that makes the water safe for use on lawns, golf courses, parks, and other places that people
frequent. In Hawaii, more and more projects are using R-1 water.
R-2 is slightly lower quality recycled water. R-2 is secondary (biologically) treated wastewater
that has also been disinfected. Its use requires more caution and restrictive controls than R-1
water.
R-3 is the least pure class of recycled water. R-3 quality water is wastewater that has been treated
to the secondary level. It can only be used for irrigation at places where people rarely go.
Recycled water is utilized on most of the main islands in Hawaii. Golf courses, agriculture, and
landscapes are irrigated with recycled water. Some of the golf courses that use water include
the Experience at Koele, Ka‘anapali Golf Course, Hawaii Kai Golf Course, Kaua‘i Lagoons
and Waikaloa Resort. Agricultural uses include seed corn irrigation on Maui and Kaua‘i and at
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-13
Hawaii Reserves on Oahu where bananas, papayas, and ornamental plants are grown. Landscape
irrigation projects include Kalama Park and the Kihei Public Library on Maui, Mauna Loa
Highway beautifi cation on Moloka‘i and the Brigham Young University-Hawaii campus on Oahu.
On Maui, the Kihei Effl uent Reuse System is the fi rst application in Hawaii of an effl uent reuse
system pressurized by an elevated closed reservoir, making the effl uent available to customers
on a continuous basis. Customers can simply connect to the system and use the effl uent without
the use of booster pumps. Purple fi re hydrants let people know that they are connecting to the
reclaimed water system. The system has met its goal of providing the County of Maui with a
system that is benefi cial to the community by preserving its potable water resources, and utilizing
reclaimed water for irrigation of parks, landscape areas and a golf course, and for fi re protection.
The reclaimed water is also used by a major agricultural operation, Monsanto Corporation, for the
production of high quality seed corn that is marketed worldwide. The system has proven to be
easy to operate and reliable, and has met the needs and expectations of the County.
4.7 Servicing Options for Rural Communities
When it comes to providing wastewater services for a rural community, it is usually a balancing
act to provide both clean drinking water and effective wastewater disposal while striving to
maintain the village character that makes a rural community appealing. There is a continuum
represented by onsite water and wastewater services versus centralized water and wastewater
services that contains both positive and negative features or outcomes. This continuum can be
expressed visually by the “wheel” depicted in Figure 4-2 below. Positive aspects of the continuum
are shown in black text and negative aspects of the continuum are shown in white text.
Figure 4-2.
The Rural Servicing “Wheel”The Rural Servicing “Wheel”
Source: Horsley Witten Group, IncSource: Horsley Witten Group, Inc..
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-14
The main concern with using both private wells and septic systems in any setting is the cross
contamination of the private well caused by the pumping of groundwater containing septic
system effl uent. The effl uent can be from the septic system on the same lot, or from one located
on an adjacent or nearby lot. Small lots and denser development increases the potential for cross
contamination as wells and septic systems are placed closer together, often close to the required
setback distance. If very small lot sizes are desired, it may not be feasible to use private services,
as it will not be possible to maintain the required setbacks.
The growth of a village using private services can also be limited by the local soils or geologic
conditions that may limit the use of onsite septic systems or private wells. Tight soils or shallow
depths to groundwater on a small lot may make it impossible to properly site a septic system.
The ability to install a well that provides an adequate volume of potable water may also be
limited. If the village is adjacent to surface waters or wetlands, the use of onsite septic systems
may impact these resources through discharges of nitrogen and phosphorus.
Adjacent properties can utilize a shared septic system to discharge wastewater, eliminating
the need for a system on each individual lot. This approach can be used in areas where septic
systems are being upgraded, and there are space constraints on some lots, but not on others.
The shared system can be a standard system, or could include components to provide advanced
treatment. One caveat relating to the use of shared systems is that they can create more
development than intended. For example, Lot A and Lot B are adjacent lots that are currently
vacant. The physical characteristics of Lot B may be such that it cannot support an individual
on-site wastewater disposal system and therefore no dwelling can be built. However, the
physical characteristics of Lot A may be such that it can accommodate wastewater from more
than just a single dwelling. In this situation, Lot B may now be built as the dwelling on Lot B
will share the drainfi eld that is being built to service the new dwelling on Lot A. Because of the
use of a shared system, a previously “un-buildable” lot has now been made “buildable,” and this
can be an undesired consequence of utilizing shared systems if a community is trying to control
growth.
A clustered wastewater system as discussed in this workbook is essentially a larger version of
a shared system, and may serve an entire subdivision. The use of a clustered system allows for
greater fl exibility in the siting of private wells on individual lots, and can maximize development
in areas that would otherwise be limited by private well setback distances, local soils and depth
to water constraints. Clustered systems can include advanced treatment, with the level of
treatment a function of the environmental and public health issues in the vicinity of the system.
A village can be developed or maintained using a centralized water system, a centralized
wastewater treatment system or both. The use of one or both of these systems avoids the cross
contamination concerns with private wells and septic systems. Centralized water provides
the opportunity to manage water quality issues better than with private wells, and centralized
wastewater can offer many treatment advantages over standard septic system treatment of
wastewater.
The design, construction and management of private onsite septic systems and private or
public cluster or centralized service systems has evolved considerably over the last 20 – 30
years. To a great degree, this evolution has been led by the environmental, public health and
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-15
land use planning confl icts that result from the pressures of increased development using onsite
wastewater services.
Today, there are many examples of best practices and innovative solutions to remedy both
existing problems in growing communities and optimize land use in new rural development. The
information provided in the following matrix is intended to illustrate the variety of approaches
and strategies to wastewater management. Benefi ts and drawbacks for each approach or
strategy have been provided in the matrix, beginning on the next page, in terms of engineering/
implementation, land use planning and public health/environmental protection perspectives.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-16
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LID WORKBOOK: A PRACTITIONER’S GUIDE 4-27
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-28
4.8 Opportunities to Implement Alternative Wastewater Strategies
As mentioned earlier, the Hawaii DOH does allow the use of some alternative septic system
technologies such as composting toilets and constructed wetlands. However, a number of the
technologies described in this Chapter can only be used following approval by DOH as an
experimental system. This process may discourage the use of systems that can provide for
nutrient, and possibly, pathogen removal.
Other states in the country have developed a process of pre-approving alternative technologies
to foster their use in appropriate applications. For example, the State of Massachusetts has an
extensive list of approved technologies for use in on-site septic system designs. This allows
developers and health offi cials to select and use a technology that can provide for a higher
quality effl uent. It also allows them to obtain credits, or waivers, in the design of systems, such
as for an increase in fl ow in nitrogen sensitive areas (using a system that removes nitrogen), a
reduction in leaching fi eld size, or a reduction in the depth to groundwater. Many of these credits
also facilitate the use of alternative technologies in the upgrade of existing systems in dense
communities located in sensitive areas.
The list of Massachusetts approved technologies is provided below. This list is shown as an
example because of the extensive number of technologies that have been approved. Each
approval is provided by the state Department of Environmental Protection in a letter that
provides the design and operation and maintenance requirements for the technology. Further
information on the approval process and the alternative technologies is provided at www.mass.
gov/dep/water/wastewat.htm. Oregon’s Department of Environmental Quality has a similar
approval process, although the number of approved technologies are not as extensive www.
deq.state.or.us/wq/onsite/aattechnology.htm .
Hawaii could consider a similar pre-approval process to facilitate the use of septic system
technologies that could improve groundwater and surface water quality in sensitive watersheds.
This could potentially encourage the Counties to require the use of these systems in new
construction, and could aid in the upgrade of existing systems in sensitive areas.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-29
Certified for General Use
Click here for approval letters and O&M checklists for all technologies certified for general use.
Technology Model(s)Company Technology
Description
Approved Use
Composting
Toilets
Compliant with
Title 5
Generic Composting
Toilet
Composting toilets as
described in Title 5 (310
CMR 15.289 (3)(b))
Biolet XL Composting
Toilet
Biolet USA, Inc.
150 East State Street
Newcomerstown, OH
43832
Composting
Toilet
Equivalent to
composting toilets as
described in Title 5 (310
CMR 15.289 (3)(b))
Sun-Mar Compliant with
Title 5
Sun-Mar Corp.
5370 South Service
Rd.
Burlington, ON,
L7L 5L1
Composting
Toilet
Equivalent to
composting toilets as
described in Title 5 (310
CMR 15.289 (3)(b))
Recirculating
Sand Filter
Compliant with
Title 5
Generic Sand Filter BOD5 and TSS removal
Nitrogen reduction
RUCK Systems less
than 2000 gpd
Innovative RUCK
Systems, Inc.
200 Main Street
Falmouth, MA 02540
Filter Nitrogen Reduction
Equivalent to
conventional Title 5
system
FRALO SEPTECH
Poly Tanks
ST-1060, ST-
1250 and ST-1500
FRALO Plastech
Manufacturing, LLCOne General Motors
Drive
Syracuse, NY 13206
Polyethylene
septic tank
Equivalent to
conventional septic tank
Advantex Advantex AX20 Orenco Systems, Inc.
814 Airways Avenue
Sutherlin, OR 97479
Textile filter
SeptiTech Treatment
System
400, 550, 750, 1200, 1500,
3000H
SeptiTech, Inc.
220 Lewiston Road
Gray, ME 04039
Trickling Filter
Intermittent Sand Filter by
Orenco Systems,
Inc.
Low-Rate Saneco, Inc. Box 9B 65 Eastern
Avenue
Essex, MA 01929
Sand Filter
Bioclere 16, 22, 24, 30,
and 36 series
Aquapoint
241 Duchaine Blvd.
New Bedford, MA
02745
Trickling Filter
Cromaglass WWT
Systems
CA-5, CA-12,
CA-25, CA-30,
CA-50, CA-60,
CA-100, CA-120,
and CA-150
Cromaglass
Corporation
P.O. Box 3215
2902 N. Reach Road
Williamsport, PA
17701
Sequencing
Batch Reactor
JET Aerobic
Wastewater Treatment
JET-500, JET-
750, JET-1250, JET-1500
Clearwater Recovery
175 Spring Street Rockland, MA 02370
Aerobic
Treatment Unit
FAST MicroFAST, High
Strength FAST, and NitriFAST
Bio-Microbics, Inc.
8450 Cole Parkway Shawnee, KS 66227
Aerobic
Treatment Unit
FAST Modular FAST Smith & Loveless, Aerobic
Equivalent to
conventional Title 5
system
List of Approved Alternative Technologies
Massachusetts Department of Environmental Protection
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-30
Certified for General Use
Click here for approval letters and O&M checklists for all technologies certified for general use.
Technology Model(s)Company Technology
Description
Approved Use
Inc.
14040 Santa Fe Trail
Drive
Lenexa, KS 66215
Treatment Unit
Norweco Singulair 960
and 960 DN
Siegmund
Environmental
Services, Inc.
49 Pavilion Avenue
Providence, RI 02905
Aerobic Treatment Unit
Amphidrome Amphidrome
Process
F.R. Mahony &
Associates, Inc.
131 Weymouth
Street
Rockland, MA 02370
Submerged
Attached-
Growth
Sequencing
Bioreactor
Waterloo Biofilter Waterloo Biofilter
System, Inc.
143 Dennis Street
Rockwood, ONT,
N0B 2K0
Trickling Filter
Eljen Xpandable
Chamber
XP1607 through
XP 3614
Eljen Corporation
125 McKee Street
East Hartford, CT
06108
Alternative SAS
EZ Flow EZ1202V,
EZ1203T,
EZ1203H,
EZ1402V,
EZ1203 Bed,
EZ1203 Mound
Ring Industrial
Group/EZ Flow
65 Industrial Park
Road
Oakland, TN 38060
Alternative SAS
Hancor Enviro
Chambers
Standard
Capacity, High
Capacity, and
Narrow
Hancor, Inc
401 Olive Street
Findlay, OS 45840 Alternative SAS
Alternative SAS in trench, bed, or gallery
configurations
BioDiffuser
Chambers
Biodiffuser 14
inch and 16 inch
High Capacity,
11 inch Standard
and Bio 2 and
Bio 3 Biodiffusers
Advanced Drainage
Systems, Inc.
4640 Trueman
Boulevard
Hilliard, OH 43026
Alternative SAS
Cultec Chambers EZ-24,
Recharger 280
and 400
Cultec Chambers Contactor 75,
100, 125;
Recharger 180 and 330
Cultec Chambers Contactor Field
Drain C1, C2, C3, and C4
Cultec, Inc.878 Federal Road
Brookfield, CT 06804
Alternative SAS
Infiltrator High Capacity Infiltrator Systems, Alternative SAS
Alternative SAS in
trench, bed, or gallery
configurations with 40%
reduction in size with
effluent loading rates
specified in Title 5 (310
CMR 15.242).
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-31
Certified for General Use
Click here for approval letters and O&M checklists for all technologies certified for general use.
Technology Model(s)Company Technology
Description
Approved Use
Chambers Chamber,
Standard
Chamber,
Infiltrator 3050
(Storm Tech SC-740) and
Equalizer 24 and
36
Inc.
P.O. Box 768
6 Business Park Road
Old Saybrook, CT
06475
Eljen In-Drain
Systems
Type B43 and
A42
Eljen Corporation
125 McKee Street
East Hartford, CT
06108
Alternative SAS
Enviro-Septic
Leaching System
Enviro-Septic Presby Enviromental
Inc.
Route 117, PO Box
617
Sugar Hill, NH 03586
Alternative SAS
** Bed only
^ back to top
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-32
Approved for Piloting
Click here for approval letters and O&M checklists for all technologies approved for piloting use.
Technology Model(s)Company Technology
Description
Approved Use
Omni Recirculating
Sand Filter System
RSF System OMNI Environmental
Systems, Inc.
P.O. Box 128/465
East Falmouth Hwy
Falmouth, MA 02536
Recirculating Sand
Filter
Cromaglass WWT
System
CA-5D, CA-
12D, CA-25D,
CA-30D, CA-
50D, CA-60D,
CA-100D, CA-
120D, and
CA-150D
Cromaglass
Corporation
P.O. Box 3215
2902 N. Reach Road
Williamsport, PA 17701
Sequencing Batch
Reactor
Amphidrome Process Amphidrome
Process
F.R. Mahony &
Associates, Inc.
131 Weymouth Street
Rockland, MA 02370
Submerged
Attached-Growth
Sequencing
Bioreactor
Norweco Singulair 960
DN
Siegmund
Environmental
Services, Inc.
49 Pavilion Avenue
Providence, RI 02905
Aerobic
Treatment Unit
Nitrex Nitrex Filters
and Nitrex
Plus Filters
Lombardo Associates,
Inc.
49 Edge Hill Road
Newton, MA 02467-
1170
Filter with
nitrate-reactive
media
BOD5 and TSS
removal
Nitrogen
reduction
RID RID
Phosphorus
Removal
System
Lombardo Associates,
Inc.
49 Edge Hill Road
Newton, MA 02467-
1170
Upflow filter Phosphorus
removal
Waterloo Biofilter Waterloo Biofilter
System, Inc.
143 Dennis Street
Rockwood, ONT, N0B
2K0
Trickling Filter Increased
loading rates
and reduced
separation to
groundwater
SeptiTech Treatment
Systems
400N, 550N,
750N,
1200N,
1500N,
3000N,
SeptiTech
Engineered
Systems
SeptiTech, Inc.
220 Lewiston Road
Gray, ME 04039
Enhanced
recirculating
biological trickling
filter
BOD5 and TSS
removal &
Nitrogen
reduction
RUCK CFT System North Coast Technologies, LLC
200 Main Street, Suite
201 Falmouth, MA 02540
Aerobic RUCK filter
OAR OAR System Environmental
Operating Solutions,
Aerobic reactor
with Bio-
Nitrogen
reduction
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-33
Approved for Piloting
Click here for approval letters and O&M checklists for all technologies approved for piloting use.
Technology Model(s)Company Technology
Description
Approved Use
Inc.
230 Jones Street
Falmouth, MA 02540
augmentation
^ back to top
Approved for Remedial Use
Click here for approval letters and O&M checklists for all technologies approved for remedial use.
Technology Model(s)Company Technology
Description
Approved Use
White Knight
Inoculator /
Generator
Alternative
Treatment
System
Bacterial
Augmentation
and Aeration
System
Knight
Treatment
Systems
281 County
Route 51A
Oswego, NY
13126
Piranaco
Alternative
Treatement
System
Bacterial
Augmentation
and Aeration
System
Piranaco
1875 Joy Road
Occidental, CA
95465
Bio-
augmentation
Renovation of failed SAS
Geoflow
Subsurface
Drip
Wastewater
Disposal
System
Drip Irrigation
System
Geoflow Inc.
500 Tamal
Plaza, Suite 506
Corte Madera,
CA 94925
Alternative
SAS
Alternative SAS trench-drip
irrigation
Perc-Rite
Subsurface
Drip
Wastewater
Disposal
System
Drip Irrigation
System
American
Manufacturing
Co. Inc.
P.O. Box 549
Manassas, VA
20108-0549
Alternative
SAS
Alternative SAS trench-drip
irrigation
Composting
Toilets
Compliant with
Title 5
Generic Composting
Toilet
Composting toilets as described in
Title 5 (310 CMR 15.289 (3)(b))
Recirculating
Sand Filters
Compliant with
Title 5
Generic Sand Filter
The Clean
Solution
Alternative
Models: 250,
250 PT,
250ST3,
250ST4, 600,
1000, 1750,
2500, 3100
and 10000
Wastewater
Alternatives of
New England,
LLC
27 Kensington
Road
Hampton Falls,
NH 03844
Submerged
media
biological
treatment
Puraflo Peat Fiber
Biofilter
Bord na Mona
Environmental
Products U.S.
Inc.
4106 Bernau
Peat Filter
BOD5 and TSS removal
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-34
Approved for Remedial Use
Click here for approval letters and O&M checklists for all technologies approved for remedial use.
Technology Model(s)Company Technology
Description
Approved Use
White Knight
Inoculator /
Generator
Alternative
Treatment System
Bacterial
Augmentation
and Aeration
System
Knight
Treatment
Systems
281 County
Route 51A Oswego, NY
13126
Piranaco
Alternative
Treatement
System
Bacterial
Augmentation
and Aeration
System
Piranaco
1875 Joy Road
Occidental, CA
95465
Bio-
augmentation
Renovation of failed SAS
Geoflow
Subsurface
Drip
Wastewater
Disposal
System
Drip Irrigation
System
Geoflow Inc.
500 Tamal
Plaza, Suite 506
Corte Madera,
CA 94925
Alternative
SAS
Alternative SAS trench-drip
irrigation
Avenue
Greensboro, NC
27407
Jet Home
Aerobic
Wastewater
Systems
J-500, J-750,
J-1000, J-
1250, and J-
1500
Clearwater
Recovery
(Stephen B.
Nelson)
175 Spring
Street
Rockland, MA
02370
Aerobic
treatment
system
Amphidrome Amphidrome
Process
F.R. Mahony &
Associates, Inc.
131 Weymouth
Street
Rockland, MA
02370
Submerged
Attached-
Growth
Sequencing
Bioreactor
Orenco
Intermittent
Sand Filter
Low-Rate Filter Saneco, Inc.
Box 9B 65
Eastern Avenue
Essex, MA 01929
Sand Filter
Norweco Singulair
Systems
960N,
960/750,
960/1000,
960/1250, and
960/1500
NORWECO, Inc.
220 Republic
Street
Norwalk, OH
44857
Aerobic
treatment
Waterloo
Biofilter
Biofilter Waterloo
Biofilter System,
Inc.143 Dennis
Street
Rockwood, ONT,
N0B 2K0
Trickling
Filter
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-35
Approved for Remedial Use
Click here for approval letters and O&M checklists for all technologies approved for remedial use.
Technology Model(s)Company Technology
Description
Approved Use
White Knight
Inoculator /
Generator
Alternative
Treatment System
Bacterial
Augmentation
and Aeration
System
Knight
Treatment
Systems
281 County
Route 51A Oswego, NY
13126
Piranaco
Alternative
Treatement
System
Bacterial
Augmentation
and Aeration
System
Piranaco
1875 Joy Road
Occidental, CA
95465
Bio-
augmentation
Renovation of failed SAS
Geoflow
Subsurface
Drip
Wastewater
Disposal
System
Drip Irrigation
System
Geoflow Inc.
500 Tamal
Plaza, Suite 506
Corte Madera,
CA 94925
Alternative
SAS
Alternative SAS trench-drip
irrigation
AdvanTex
Treatment
Systems
AX-15, AX-20
and AX-100
Orenco
Systems, Inc.
814 Airways
Avenue
Sutherlin, OR
97479
Textile media
aerobic
treatment
FAST Modular FAST Smith &
Loveless, Inc.
14040 Santa Fe
Trail Drive
Lenexa, KS
66215
Aerobic
Treatment
Unit
FAST MicroFAST,
High Strength
FAST, and
NitriFAST
Bio-Microbics,
Inc.
8450 Cole
Parkway
Shawnee, KS
66227
Aerobic
Treatment
Unit
SeptiTech
Treatment
Systems
300, 400, 550,
750, 1200
3000, and
SeptiTech
Engineered
Systems
SeptiTech, Inc.
220 Lewiston
Road
Gray, ME 04039
Aerobic
Treatment
unit
Cromaglass
Wastewater
Treatment
System
CA-5, CA-12,
CA-15, CA-25,
CA-30, CA-50,
CA-60, CA-100, CA-120,
CA-150
Cromaglass
Corporation
P.O. Box 3215
2902 N. Reach Road
Williamsport, PA
17701
Sequencing
Batch Reactor
Bioclere 16, 22, 24, and
30 series
Aquapoint
241 Duchaine
Blvd.
New Bedford, MA
Trickling Filter
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-36
Approved for Remedial Use
Click here for approval letters and O&M checklists for all technologies approved for remedial use.
Technology Model(s)Company Technology
Description
Approved Use
White Knight
Inoculator /
Generator
Alternative
Treatment System
Bacterial
Augmentation
and Aeration
System
Knight
Treatment
Systems
281 County
Route 51A Oswego, NY
13126
Piranaco
Alternative
Treatement
System
Bacterial
Augmentation
and Aeration
System
Piranaco
1875 Joy Road
Occidental, CA
95465
Bio-
augmentation
Renovation of failed SAS
Geoflow
Subsurface
Drip
Wastewater
Disposal
System
Drip Irrigation
System
Geoflow Inc.
500 Tamal
Plaza, Suite 506
Corte Madera,
CA 94925
Alternative
SAS
Alternative SAS trench-drip
irrigation
02745
Jet J-335 Tertiary
Sand Filter
Clearwater
Recovery
(Stephen B.
Nelson)
175 Spring
Street
Rockland, MA
02370
Sand filter NA
Enviro-Septic Enviro-Septic
System
Presby
Enviromental
Inc.
Route 117, PO
Box 617
Sugar Hill, NH
03586
Alternative
SAS Alternative SAS in bed
configurations with 40% reduction
in size with effluent loading rates
specified in Title 5 (310 CMR
15.242).
Eljen In-Drain
Systems
Type B43 and
A42
Eljen Corporation
125 McKee Street
East Hartford, CT
06108
Alternative
SAS
Alternative SAS in trench, bed, or
gallery configurations with 40% reduction in size with effluent
loading rates specified in Title 5
(310 CMR 15.242).
^ back to top
I/A Technologies with Nitrogen Reduction Credit
A number of the technologies listed above have received nitrogen reduction credit as part of their
technology approvals:
General Use Certification
Recirculating Sand Filters
RUCK
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-37
Provisional Use Approvals
Advantex
Amphidrome
Bioclere
MicroFAST, High Strength FAST, NitriFAST, and Modular FAST
Waterloo Biofilter
Piloting Use Approvals
Amphidrome Process
Cromaglass WWT System
Nitrex-Nitrex Plus
Norweco Singulair
OAR
OMNI Recirculating Sand Filter System
RUCK CFT SeptiTech
^ back to top
Technologies Under Review by MassDEP
Technology Company Technology
Description
Proposed MassDEP
Approval
WAI BioCon Wastewater Alternatives
of NE, Inc.
Aerated submerged
media biological
contractor
Remedial
WAI BioCon Wastewater Alternatives
of NE, Inc.
Aerated submerged
media biological
contractor
General
GeoFlow Drip GeoFlow Drip Irrigation General Use
MBR Bio-Microbics Membrane Reactor Piloting
Singulair Seigmund
Environmental
Aerated Biological
Contractor
Provisional
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-38
4.9 Case Studies
One of the purposes of this workbook is to demonstrate that there can be solutions to even the
most challenging wastewater servicing problems. The following case studies illustrate how other
communities have addressed serious servicing issues. While not all of the case studies may be
applicable to Hawaii, they do serve to confi rm that through a combination of determination and
innovation (and not necessarily more money), most problems can be addressed.
Many of the case studies are from island communities, like Hawaii. Such communities represent
the extreme conditions of a limited resource base such as fresh water. When faced with growth
pressures, island communities require some of the most innovative wastewater servicing
solutions.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-39
Program Description
The constructed wetland system is the cornerstone of Arcata’s urban watershed renovation program. This
program includes major urban stream restoration, log pond conversion to a swamp habitat, pocket wetlands
on critical reaches of urban streams, and an anadramous wastewater aquaculture program to restore critical
commercial, recreational, and ecological important populations. The Arcata project is a demonstration of
wastewater reuse, ecological restoration, and reuse of industrial, agricultural and public service land.
Arcata Site Plan
Situated in the heart of the redwood country and along the rocky
shores of the Pacifi c Northcoast, the City of Arcata is located
on the northeast shore of Humboldt Bay in Northern California,
280 miles north of San Francisco. Arcata, with a population
of approximately 15,000, is a diverse community whose
resourcefulness and integrity has demonstrated that a constructed
wetland system can be a cost effi cient and environmentally sound
wastewater treatment solution. In addition to effectively fulfi lling
wastewater treatment needs, Arcata’s innovative wetland system
has provided an inspiring bay view window to the benefi ts of
integrated wetland enhancement and wastewater treatment.
What is the Arcata Marsh and Wildlife Sanctuary?
Arcata is a small town located on the northeastern side of Humboldt Bay, about 280 miles north of San
Francisco. Humboldt Bay is a focal point where timber resources and marine resources cross paths as
they struggle to sustain Humboldt County’s economy. Resource management is a practice that receives
high priority and expert advice in this scenic niche of the Pacifi c North coast. Arcata, with a population
of approximately 15,000, is a diverse community whose resourcefulness and integrity has served to lead
the city down a successful path marked by innovative decisions and maintained by pride. So, when the
city faced making a change in their wastewater treatment methods, they demonstrated that a constructed
wetland system can be a cost effi cient and environmentally sound wastewater treatment solution. In addition
to effectively fulfi lling wastewater treatment needs, Arcata’s innovative wetland system has provided an
inspiring bay view window to the benefi ts of integrated wetland enhancement and wastewater treatment.
A Natural System for Wastewater Reclamation
and Resource Enhancement
Arcata, California
Community Information
Status: City
Population: 17,000
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-40
How did the project evolve?
Arcata established its innovative treatment system as a result
of extensive community involvement and a series of political
events. In the early 1970’s, Arcata’s active wastewater
treatment plant discharged unchlorinated primary effl uent
into Humboldt Bay. In 1974 the State of California enacted
a policy which prohibited discharge of wastewater into bays
and estuaries unless enhancement of the receiving water
was proven. In response to this policy the local Humboldt
Bay Wastewater Authority proposed the construction of a
state sponsored regional wastewater treatment plant that
would serve all the communities in the Humboldt Bay
vicinity. The plant was to have large interceptors around
the perimeter of the bay with a major line crossing under
the bay in the region of active navigation. The proposed
treatment facility was energy intensive, with signifi cant
operational requirements. Effl uent from the proposed plant
was to be released offshore into an area of shifting sea bottom and heavy seas during winter storms. As the
scale of the regional treatment plant grew, the costs and diffi culties of incorporating other communities
became apparent.
Recognizing the constraints of the local environment and criteria for wastewater treatment, the City of
Arcata began exploring the design of a decentralized system, which employed constructed wetlands.
Wastewater aquaculture projects at the City of Arcata started as early as 1969 and had been successful in
raising juvenile Pacifi c Salmon and Trout in mixtures of partially treated wastewater and seawater. This
project demonstrated that wastewater was a “resource” that could be reused and not simply to be viewed as
a disposal problem. With this philosophy a city Task Force on Wastewater Treatment determined that the
natural processes of a constructed wetland system could offer the city an effective and effi cient wastewater
treatment system. From 1979 to 1982 the city, and associated proponents of alternative wastewater
treatment, experimented with partially treated wastewater and the natural processes of wetland ecosystems.
These experiments demonstrated that constructed freshwater wetlands could be utilized to treat Arcata’s
wastewater and at the same time enhance the biological productivity of the wetland environment into
which treated wastewater was discharged. The Task Force determined that a constructed wetland system
was extremely cost effective. Moreover, a successful system offers the city a vital wetland ecosystem that
could be used for the rearing of salmon and steelhead as well as offer the community a unique site for
recreation and education.
With the aid of the Arcata City Council and political representatives in the state capital, the city received
authorization in 1983 to develop the constructed wetland system and incorporate its use at the original
Arcata Wastewater Treatment Plant. The wetland system that exists today was completed in 1986. Since
that time the natural ability of marsh plants, soils and their associated microorganisms has successfully been
utilized to meet the need for a cost-effective and environmentally sound wastewater treatment technology
that meets federal and state mandated water quality requirements.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-41
Who cares and what are the benefi ts?
At the same time that wetland wastewater
technology has been used to successfully
meet water quality criteria, it has also
aided in restoring a degraded urban
waterfront. Prior to the installation of
its wetland treatment system, the City
of Arcata’s waterfront was the site of an
abandoned lumbermill pond, channelized
sloughs, marginal pasture lands, and a
closed sanitary landfi ll. Today, Arcata’s
waterfront has been transformed into
100 acres of freshwater and saltwater
marshes, brackish ponds, tidal sloughs
and estuaries. Because of the wetland
communities and wildlife habitats that
the waterfront now supports, the area in
its entirety has come to be known as the
Arcata Marsh and Wildlife Sanctuary
(AMWS.) The AMWS’s three freshwater
wetlands are Gearheart, Allen and
Hauser Marshes. They were constructed
to receive treated wastewater, thereby treating the wastewater further and enhancing the receiving water at
the same time. These enhancement marshes are a host of aquatic vegetation that, in association with Klopp
Lake and the adjacent estuaries and ponds, have further provided an extraordinary habitat for shorebirds,
waterfowl, raptors and migratory birds.
As a home or rest stop for over 200 species of birds, the AMWS has developed a reputation as one of
the best birding sites along the Pacifi c North Coast. The Redwood Region Audubon Society uses the site
on a regular basis for its weekly nature walks. For the past 10 years, docents trained by the Society have
explained the role the wetlands play in attracting birds and mammals, as well a s their role in managing
the water quality of Humboldt Bay. The beauty and uniqueness of the AMWS has served as inspiration to
many artists, whose products range in form from plays and poems to photographs and paintings.
Arcata has become an international model of appropriate and successful wastewater reuse and wetland
enhancement technologies. Over 150,000 people a year use the AMWS for passive recreation, bird
watching, or scientifi c study. Visitors from around the world have come to Arcata to investigate its success
in wastewater management. Students of all ages and institutions use the AMWS for scientifi c study. In
1987, the City of Arcata was selected by the Ford Foundation to receive an award for this wastewater
wetlands project as an innovative local government project. This award included a $100,000 prize to
be used to fund the establishment of the Arcata Marsh Interpretive Center. The Center focuses on the
historical, biological and technical aspects of the AMWS, and attempts to meet the informational and
educational demands of the wastewater treatment system.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-42
Program Description
Cedar Lake Township is located in southeastern Minnesota on the shores of Cedar Lake. Like many
lakeside communities in Minnesota, it is experiencing increased residential activity as former urbanites
head to the country to live in their “dream” home. Many of the homes around Cedar Lake were built with
on-site septic systems, systems which many urbanites are not familiar with. In 1997, many homeowners in
Cedar Lake realized that their septic systems were outdated and did not meet state or county codes. In an
effort to limit the pollutant load to the lake through substandard and failing septic systems, local residents
were avoiding using their washing machines and sink disposals. The residents of Cedar Lake formed an
association to begin to investigate their wastewater management options, and decided to install a cluster
wastewater treatment system.
The chosen wastewater treatment system was a pressure sewer system tied to a regional treatment plant.
Characteristics of lake area topography, such as high groundwater, rolling hills, or rocky terrain, usually
make the installation of a conventional gravity system costly. A pressure sewer system may be installed for
30-50% less than a conventional system in these areas. In addition to the potential economic advantage,
pressure sewer systems have much less of an impact to the surrounding area when they are installed.
Because they do not rely on gravity, system piping can be laid to follow the contour of the land. In
addition, trenches are not needed for installation of sewer pipe. Instead, directional drilling, a technique
frequently used in the oil industry, can be used to bore horizontal holes
into which the piping is laid. This drilling method leads to less disruption
of the landscape. In Cedar Lake, residents wanted to avoid the disruption
caused by trenching. In addition, the estimated cost of a pressure system
was $3,300,000 USD, 1.2 million USD less than a conventional gravity
system. These cost numbers also refl ect the construction of a force main
to an existing regional wastewater treatment plant.
Each home in Cedar Lake is equipped with a small grinder pump station
buried in the yard. Wastewater from the home fl ows into the pump
station where grinder blades shred the solids into a slurry. The system
then collects the sewage in a “ring route” of in-ground, gravelless 25.4-
cm diameter corrugated polyethylene pipe that circles the lake and leads
to a larger pumping station. This larger pumping station pumps
Pressure Sewer Systems for a
Small Lakeside Community
Cedar Lake, Minnesota, USA
Community Information
Status: Township
Population: 2,299
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-43
the wastewater to the New Prague Wastewater Treatment Plant for
treatment and eventual disposal. This pumping station is located away
from the residents homes and away from the lake.
Additional Program Description
Process for Selection: Consultant assistance
Operational Date: July, 2002
Capital Cost: $3,300,000 capital (estimated)
Operation Cost: $432 USD/year/household (estimated)
Management Model: Wastewater District
Legal Actions Needed: Establishment of “Cedar Lake Area Water and Sanitary Sewer District” in state
legislature
Indicators of Success: Residents may now use washing machines and sink disposals again
Lessons Learned: N/A
Cost Information
Residents in the Cedar Lake Water & Sewer District are subject to regulations, connection fees, and
treatment charges imposed by the City of New Prague. Each homeowner will be charged a monthly fee
estimated at $36 USD ($432 USD per year). This fee covers the operation, maintenance and replacement
costs, as well as monthly treatment fees paid to the City of New Prague.
Contact Information
Mr. Bob Brautigam
Cedar Lake Area Water and Sanitary Sewer District
952-758-2364
Related Links
http://www.bolton-menk.com/news/pdf/newsletter2-2002.pdf
http://www.ocwagis.org/Website/downloads/Decentralized/decentralized.htm
http://www.ces.purdue.edu/extmedia/AE/ID-265.pdf
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-44
Program Description
Island Road is a narrow, unpaved road that dead-ends at the bank of the Essex River in Essex, Massachusetts.
The Town of Essex is a small town located about 55 kilometers north of Boston. There is no town sewer,
and residents outside of the village center rely on private well water. The Essex River is a brackish,
estuarine system heavily infl uenced by the tides. Four homes were located at the end of Island Road, in
close proximity to the Essex River and its commercial shellfi sh beds. Due to contamination in the Essex
River, the Town of Essex was forced by the Commonwealth of Massachusetts to inspect every septic
system in Town and require homeowners to upgrade their septic systems if they were found to be failing.
All four septic systems at the end of Island Road were found to be failing; however, no property owner
had soil conditions such that the systems could be individually repaired on-site in accordance with state
regulation.
A property owner further up Island Road, away from the River, decided to build a house on her relatively
large (.4+ hectare) lot. As her lot was further from the River, soil conditions were much more suitable
for installing an on-site septic system. Approached by the four homeowners on the end of Island Road,
she agreed to allow them to construct a shared leaching facility on her property. As shared septic systems
where still unique in Massachusetts at that point in time, the four homeowners received a $50,000 USD
grant to aid in the construction of the shared septic system.
Construction of the system could not proceed until an easement had been granted to allow the four
homeowners to dispose of their wastewater on the neighboring property. The Trust also developed a
maintenance “Covenant” to ensure that any needed repairs to the shared system would occur and be funded
by the four property owners and to ensure that the system would be inspected annually by a state-licensed
inspector. The Covenant was approved by the state’s Department of Environmental Protection, who also
reviewed the plans for the shared system. This Covenant was recorded with the Registry of Deeds.
Island Road Shared Septic System
Essex, Massachusetts
Community Information
Status: Town
Population:3,267
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-45
Additional Program Information
Capital Cost: < $100,000.00 USD
Management Model: Shared Septic System
Operation Cost: Routine maintenance (pump-outs), annual inspection fees, legal fees for maintenance
of Covenant and easement
Indicators of Success: Four failed septic systems adjacent to environmentally sensitive shellfi sh beds
have been removed and replaced with one septic system that discharges properly treated sewage away
from the shellfi sh beds.
Lessons Learned: In a remedial situation, shared systems are typically viewed as a means of last resort
as they force neighbors to rely on one another for the long term.
Contact Information
Brendhan Zubricki
Town Administrator, Town of Essex
(978) 768-6531
Related Links
http://www.essexma.org/
http://users.rcn.com/essexboh/home.shtml
http://www.gis.net/~ewd/page6.htm
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-46
Program Description
One way to ensure that a septic system is examined by a professional to determine its operational status
is to require an inspection any time the title of the property is transferred to a new owner. In the United
States, the State of Massachusetts currently requires time of transfer inspections in their regulations
governing on-site sewage treatment and disposal. The inspection has to be performed by a state-licensed
inspector using a standardized state inspection form that is submitted to both the buyer and the local health
department. Transactions in Massachusetts excluded from the inspection requirement include:
• Taking a security interest in a property, including issuing a mortgage.
• Refi nancing a mortgage, whether or not the identity of the lender remains the same.
• A change in the form of ownership among the same owners (such as placing a property in trust with
the current owners as benefi ciaries).
• Adding or deleting a spouse as an owner or benefi ciary.
• The appointment of or a change in a guardian, conservator, or trustee.
Other provisions of the time of transfer regulation cover unique circumstances such as condominiums,
foreclosure, inheritance, legal life estate, inter-family transfers, tax taking by government, levy of execution
resulting in property conveyance, bankruptcy, and other changes in ownership such as new benefi ciaries.
The regulations also provide for some exceptions to the time of transfer inspection. If an inspection has
been performed up to two years prior to the time of transfer, another inspection is not needed. This can
be extended up to three years prior to time of transfer with proof that the system has been pumped every
year since the last inspection. If the system was newly installed within the last two years an inspection is
not required. Some communities may have comprehensive septic inspection programs, approved by the
state, that ensure every system in the community is inspected at least once every seven years. In these
communities, time of transfer inspections are not required. The fi nal exception to the time of transfer
inspection requirement occurs when the person acquiring title has signed an enforceable agreement to
upgrade the septic system or to connect to a sanitary sewer within two years following the transfer of
title.
Property Transfer Septic System
Inspections
Massachusetts, USA
Community Information
Status: Commonwealth
Population:6,349,097
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-47
Additional Program Information
Capital Cost: N/A
Management Model: Mandatory Inspection Program
Operation Cost: $200.00 to $600.00 USD inspection fee (depends on complexity of system)
Indicators of Success: Hundreds of failed septic systems and cesspools across the state have been
repaired/upgraded
Lessons Learned: Involving the real estate community was an important step for acceptance of this new
regulation which took effect in 1995.
Contact Information
Massachusetts Department of Environmental Protection’s Title 5 Hotline
(800) 266-1122
Related Links
http://www.state.ma.us/dep/brp/wwm/onsite.htm
http://www.state.ma.us/dep/brp/wwm/t5regs.htm
http://www.state.ma.us/dep/brp/fi les/310CMR15.PDF
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-48
Program Description
Orange County, North Carolina, home to Hillsborough, Chapel Hill, and the University of North
Carolina, created an on-site septic system management program supervised by the Orange County Health
Department. This management program requires the inspection of on-site septic systems depending on
their engineering “complexity.” For example:
• A standard gravity-fed septic system and leachfi eld requires no regular inspection
• Any system using a pump must be inspected every fi ve years by an offi cial from the County Health
Department.
• Any “pressure dosed” or low pressure pipe system must be inspected every three years by the County
and every six months by a licensed contractor hired by the home owner. This contractor submits a
report to the County annually.
• Any system which “pre-treats” sewage effl uent, such as a sand fi lter or biofi lter system, must be
inspected annually by the County and every three months by a licensed contractor hired by the
homeowner.
State law provides the County with several ways to cover the cost of these inspections, and the County
currently charges the homeowner $100.00 USD at the time of each inspection. To make the current
program more effective, the County is considering developing educational courses to train homeowners,
inspectors, and maintenance professionals, a certifi cation program for homeowners to teach them how to
check solids levels in their tanks or help neighbors troubleshoot their systems, a technical/mechanical
manual for homeowners, and even a video on home septic system maintenance. The County also hopes
to require inspections of standard, gravity-fed septic systems via a mechanism such as requiring new
homeowners to “re-permit” their systems when a home is purchased.
Additional Program Information
Capital Cost: N/A
Management Model: Regular Inspection Program
Operation Cost: $100.00 USD per household at time of inspection
Indicators of Success: N/A
Lessons Learned: N/A
Orange County
North Carolina
Community Information
Status: County
Population:118,227
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-49
Contact Information
Jim Brown
Environmental Health Specialist
(919) 245-2360
Related Links
http://www.co.orange.nc.us/envhlth/eseptic.htm
http://www.nesc.wvu.edu/nodp/pdf/OnsiteSystem.pdf
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-50
Program Description
This small community of approximately 185 homes and businesses, located approximately 40 kilometers
west of Santa Fe close to the bank of the Rio Grande, faced a public health problem in 1985 when an
increasing number of septic tank and cesspool failures resulted in sewage “breakout.” An engineering
study found that inadequate systems, high groundwater conditions and a lack of homeowner maintenance
where the main causes of the problem. The Town decided to solve its wastewater problems through
the replacement of individual, failed on-site systems simultaneously and the establishment of an on-site
wastewater management district.
The Town organized its district under the Peña Blanca Water and Sanitation District (WSD), which has
the power to levy and collect taxes, the right to issue general obligation and revenue bonds, and the right
to require homeowners within the district to connect to a sewer system in the interest of public health and
safety. Four on-site easements were created prior to construction of new systems: a standard easement
agreement (allowed for the performance of work, access for construction and maintenance, and allows
for the payment of monthly fees), a no work easement agreement (for functioning systems not requiring
replacement, allows for the payment of monthly fees), a neighboring disposal system easement (used
where cluster systems were installed, it includes all elements of the standard easement agreement plus an
easement for disposal systems to serve adjacent homes), and a mound system easement (for properties
requiring a sand mound system, this easement allowed for the utility company to bring electrical service
to the pump). The Peña Blanca WSD took over operation of the wastewater treatment system when
construction was complete, and currently collects monthly user fees, contracts for septic tank pumping
services, and schedules the biannual pumping of every septic tank. The City of Albuquerque accepts the
septage. Users of the system pay (as of 1998) a “base” fee of $4.07 USD per month and an additional
maintenance fee of $6.57 USD per month for a 1000-gallon septic tank.
The District has no formal measures in place to monitor performance or to review the management system.
However, water samples from 16 private wells in 1998 found near background levels of nitrates in nearly
every sample, and the District has successfully changed the rate structure once.
Peña Blanca
New Mexico
Community Information
Status: Town
Population: 661
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-51
Additional Program Information
Capital Cost: $1,200,000 USD (septic leachfi elds, cluster systems, and sand mound disposal systems)
Management Model: On-Site Wastewater Management Program
Operation Cost: Monthly fee of $10.64 USD for a 1,000-gallon septic tank (covers biannual pumping
provided by WSD)
Indicators of Success: Sampling of private wells in the area found nitrate nitrogen levels below 1 mg/L
Lessons Learned: Cost effectiveness was key to allowing this solution to be implemented
Contact Information
Theresa Armijo, General Manager
Pena Blanca Water & Sanitation District
(505) 465-2512
Related Links
http://www.nesc.wvu.edu/nodp/pdf/PenaBlanca.pdf
http://www.nesc.wvu.edu/nsfc/Articles/PL/PL_f01_Web/pl_f01_NewMexico.htm
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-52
Program Description
In many areas of the U.S. Virgin Islands (USVI), there is not two to four feet of pervious soil needed to
construct a traditional on-site sewage disposal system. However, these areas may be distant from existing
public sewer lines as to make connection to these lines prohibitively expensive. As the population and level
of development of the USVI increased, it became necessary for the USVI to revise its sewage regulations
and include alternative onsite sewage disposal systems. In the USVI, this alternative system usually
consists of a constructed wetland. In this type of system, the septic tank overfl ows into a constructed
wetland where the effl uent undergoes secondary fi ltration. Plant evapotranspiration reduces the liquid
load on the system, and any effl uent remaining may be used in a “grey” water system.
The Department of Natural Resources (DNR) permits the alternative systems, whereas the Department of
Health permits traditional systems. Permits for alternative systems are allowed only after a professional
site evaluation has been performed demonstrating that the property is not suitable for a traditional system.
This evaluation is reviewed by the DNR. All zoning code setback requirements must be met. The DNR
recommends that owners of an alternative system pump the septic
tank every three to four years, much like a traditional system.
Sludge is not expected to build within the constructed wetland,
as the septic tank contains three chambers to afford the most
settling opportunities for any particles prior to effl uent discharge
to the constructed wetland. However, if sewage sludge builds
up in the wetland cells, the soil and gravel media will have to be
replaced and the wetland cells revegetated. The USVI feels that
allowing the use of alternative systems is protective of human
health and the environment and allows for the use of a property
that would otherwise be unusable.
Alternative Onsite Sewage Disposal Systems
U.S. Virgin Islands
Community Information
Status: U.S. Territory
Population: 121,000
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-53
4.10 Useful Weblinks
U.S. EPA Septic System information
http://cfpub.epa.gov/owm/septic/home.cfm
U.S. EPA Municipal Technologies information
http://www.epa.gov/owm/mtb/index.htm
National Small Flows Clearinghouse
http://www.nesc.wvu.edu/nsfc/nsfc_index.htm
Hawaii Department of Health Wastewater Branch
http://www.hawaii.gov/health/environmental/water/wastewater/index.html
Hawaii Administrative Rules Title 11 Department of Health Chp. 62 Wastewater Systems
http://www.hawaii.gov/health/about/rules/11-62.pdf
Hawaii Guidelines for the Treatment and Use of Recycled Water
http://www.hawaii.gov/health/environmental/water/wastewater/pdf/reuse-fi nal.pdf
National Sanitation Foundation certifi ed Residential Wastewater Treatment Systems
http://www.nsf.org/certifi ed/wastewater/Listings.asp?
The National Decentralized Water Resources Capacity Development Project
http://www.ndwrcdp.org/
National Onsite Wastewater Recycling Association
http://www.nowra.org/
Summary of Innovative/Alternative Technologies Approved for Use in Massachusetts
http://www.mass.gov/dep/brp/wwm/fi les/it/techsum.htm
Barnstable County Massachusetts Alternative Septic System Information Center
http://www.barnstablecountyhealth.org/AlternativeWebpage/index.htm
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-54
4.11 Annotated References
1. A Homeowner’s Guide to Septic Systems, U. S. Environmental Protection Agency, EPA-832-
B-02-005, 2002.
The information provided in the booklet is intended to help homeowners understand the function
and maintenance of their septic system.
2. Buzzards Bay Project, Final comprehensive conservation management plan, August 1991.
This plan contains recommendations for limiting nitrogen input into the Buzzards Bay estuarine
system.
3. Cantor and Knox. 1986. Septic system effects on ground water quality.
This report focuses on the various contaminants within septic system effl uent and what effects
those contaminants have on ground water quality.
4. Design Manual – Onsite Wastewater Treatment and Disposal Systems, U. S. Environmental
Protection Agency, EPA 625/1-80-012, 1980.
This design manual provides basic technical information on generic types of onsite wastewater
treatment and disposal systems and should be used as a reference document in conjunction with
the current manual (see item 10).
5. Environmental Planning for Small Communities – A Guide for Local Decision-Makers, U. S.
Environmental Protection Agency, EPA/625/R-94/009, 1994.
This book outlines a process for developing a community environmental plan.
6. Hall, M.W. 1975. A conceptual model of nutrient transport in subsurface soil systems, in
Water pollution control in low density areas, University Press of New England.
This reference discusses the movement of nitrogen in the subsurface.
7. Horsley & Witten, Inc., 1998. Coastal resource management and protection workbook.
This workbook presents a variety of challenges in managing and protecting coastal resources.
8. Large Capacity Cesspools, Memo from Hawaii DOH, August 13, 2004.
This memo explains the confl icts between Chapter 11-62 and the U.S. EPA’s UIC regulations,
and what the state is doing to resolve the confl ict.
9. Nielson, B. 1981. The consequences of nutrient enrichment in estuaries, Eutrophication
Program Report, U.S. EPA Chesapeake Bay Program, Grant No. R-806-189-010.
LID WORKBOOK: A PRACTITIONER’S GUIDE 4-55
This report discusses the negative results of excessive nitrogen inputs into an estuarine system.
10. Onsite Wastewater Treatment Systems Manual, U. S. Environmental Protection Agency,
EPA/625/R-00/008, 2002.
This manual was developed to provide supplemental and new information for wastewater
treatment professionals in both the public and private sectors and covers recent developments in
treatment technologies, system design, and long-term system management.
11. Voluntary National Guidelines for Management of Onsite and Clustered (Decentralized)
Wastewater Treatment Systems, U. S. Environmental Protection Agency, EPA 832-B-03-001,
2003.
The purpose of the Management Guidelines is to improve the level of performance of
decentralized wastewater treatment systems nationally by raising the quality of management
programs, establishing minimum levels of activity, and institutionalizing the concept of
management.
12. Wastewater Treatment Programs Serving Small Communities, U. S. Environmental
Protection Agency, EPA 832-R-02-004, 2002.
This brochure provides a brief overview of EPA and EPA-sponsored programs that provide
assistance on wastewater issues to small communities.
13. Wetzel, R.G. 1983. Limnology, Saunders Co., USA, pp. 767.
This textbook mentions the role of nitrogen in algal blooms within coastal waters.
14. Weyer, P. J. Cerhan, B. Kross, G. Hallberg, J. Kantamneni, G. Breuer, M. Jones, W. Zheng,
C. Lynch. 2001. Municipal drinking water nitrate level and cancer risk in older women: the
Iowa women’s health study, in Epidemiology, 12(3):327-338, May 2001.
This article discusses the risks of nitrates in drinking water as they relate to bladder cancer.
15. Yates, M.V. 1987. Septic tank siting to minimize the contamination of groundwater by
microorganisms, U.S. Environmental Protection Agency pub. # 440/6-87-007, 87p.
This reference contains detail on how long viruses can survive in groundwater.
LID WORKBOOK: A PRACTITIONER’S GUIDE
5-1
5 LID Resources
Better Site Design, Roadways, and Stormwater Resources
American Forests website: www.americanforests.org
American Public Transportation Association. http://www.apta.com/research/info/briefings/briefing_8.cfm. - Transit Resource Guide
American Society of Civil Engineers. 1990. Residential Streets, 2nd edition. Co-authors:
National Association of Home Builders and Urban Land Institute. Urban Land
Institute. Washington, D.C. Available at www.asce.org.
Arendt, Randall. 1994. Rural By Design. Co-authors: Brabec, Elizabth A.; Doson, Harry L.; Reid, Christine; Yaro, Robert D. American Planning Association.
Chicago, IL. Available from the American Planning Association at
www.planning.org.
Arendt, Randall. 1994. Designing Open Space Subdivisions: A Practical Step-by-Step
Approach. Natural Lands Trust, Inc. Media, PA. Available from www.natlands.org or www.greenerprospects.com.
Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to
Creating Open Space Networks. American Planning Association. Chicago, IL.
Available from the American Planning Association at www.planning.org.
Atlanta Regional Commission. August 2001. Georgia Stormwater Management Manual. Atlanta, GA.
Berkshire Regional Planning Commission. 2003. The Massachusetts Buffer Manual:
Using Vegetated Buffers to Protect our Lakes and Rivers. Prepared for the
Massachusetts Department of Environmental Protection. Boston, MA. Available from www.berkshireplanning.org.
Bioretention Fact Sheet, Federal Highway Administration. Available at
www.fhwa.dot.gov/environment/ultraur/3fs3.html.
Blankinship, Donna Gordon. Jan/Feb 2005. Creeks are Coming Back into the Light.
Article from Stormwater Magazine Vol. 6, No. 1. Forester Communications. Caledonia, MI. Available from www.stormh2o.com.
Burden, Dan. 1999. Street Design Guidelines for Healthy Neighborhoods. Co-authors:
Wallwork, Michael; Sides, Ken; Trais, Ramon; Rue, Harrison Bright. Local
LID WORKBOOK: A PRACTITIONER’S GUIDE
5-2
Government Commission Center for Livable Communities. Sacremento, CA. Available at www.lgc.org.
Capital Region Council of Governments.
http://www.crcog.org/Publications/TCSP/Ch05_Technical_TOD.pdf. -Transit-
Oriented Development - Detailed Technical Analysis.
Cappiella, K., T. Schueler, T. Wright. 2004. Urban Watershed Forestry Manual. Available from www.cwp.org.
Center for Watershed Protection. 1995. Site Planning for Urban Stream Protection.
Ellicot City, MD.
Center for Watershed Protection. 1998. Better Site Design: An Assessment of the Better
Site Design Principles for Communities Implementing the Chesapeake Bay
Preservation Act.. Center for Watershed Protection, Ellicott City, MD.
Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing
Development Rules in Your Community. Center for Watershed Protection, Ellicott
City, MD. Available from www.cwp.org.
Center for Watershed Protection. 1998. Nutrient Loading from Conventional and
Innovative Site Development. Prepared for: Chesapeake Research Consortium. Center
for Watershed Protection, Ellicott City, MD.
Center for Watershed Protection. 2000. Bioretention as a Water Quality Best
Management Practice, Article 110 from Watershed Protection Techniques. Available from www.cwp.org/Downloads/ELC_PWP110.pdf.
Center for Watershed Protection. 2000. Introduction to Better Site Design Slideshow.
Available from www.stormwatercenter.net.
Center for Watershed Protection. 2001. Redevelopment Roundtable Consensus
Agreement: Smart Site Practices for Redevelopment and Infill Practices. Center for Watershed Protection, Ellicott City, MD.
Center for Watershed Protection. 2002. The Vermont Stormwater Management Manual.
Vermont Agency of Natural Resources, Waterbury, VT. Available from
www.vtwaterquality.org/stormwater.htm.
Center for Watershed Protection. 2003. New York State Stormwater Management Design
Manual. Prepared for New York State Department of Environmental Conservation,
Albany, NY.
http://www.dec.state.ny.us/website/dow/toolbox/swmanual/#Downloads
Center for Watershed Protection. 2005. Better Site Design and Changing the
Development Rules Slideshow. Presented at New Windsor, New York, June 21-22, 2005.
LID WORKBOOK: A PRACTITIONER’S GUIDE
5-3
City of Portland, Oregon. September 2004. Stormwater Management Manual. Bureau of Environmental Services, Portland, OR. Available from
http://www.portlandonline.com/bes/.
City of Toronto Tree Advocacy Planting Program website:
http://www.city.toronto.on.ca/parks/treeadvocacy.htm
DDNREC. 1997. Conservation Design for Stormwater Management. Delaware Department of Natural Resources and Environmental Control and the Environmental
Management Centre of the Bradywine Conservancy.
Grava, Sigurd. 2003. Options Beyond Inflated Local Street Standards. Urban Planning
Program, Graduate School of Architecture, Planning, and Preservation at Columbia University. New York, NY.
Green Neighborhoods. http://www.greenneighborhoods.org/site/Index.htm. A non-profit
Massachusetts organization dedicated to educating people about OSRD development
and implementation.
Green Roofs for Healthy Cities website: www.greenroofs.org
Green Roofs.com website: www.greenroofs.com - The international greenroof industry’s resource and online information portal.
Greener Prospects. http://www.greenerprospects.com/. Web site of Randall Arendt, a
land use specialist who helped start the Open Space Residential Design movement in
Massachusetts.
Hart, Leslie. 1994. Guiding Principles of Sustainable Design. Prepared for the U.S Department of the Interior and the National Parks Service. Available from
http://www.nps.gov/dsc/dsgncnstr/gpsd/.
Institute of Traffic Engineers (ITE). 1994. Guidelines for Parking Facility Location and
Design. Institute of Traffic Engineers, Publication No. RP-022A. Available from www.ite.org.
Institute of Traffic Engineers (ITE). 1997. Designing Neighborhood Streets. Institute of
Traffic Engineers, Publication No. VHS-027. Available from www.ite.org.
Institute of Traffic Engineers (ITE). 1997. The Aesthetics of Parking. Institute of Traffic
Engineers, Publication No. LP-090A. Available from www.ite.org.
Institute of Traffic Engineers (ITE). 1999. Traditional Neighborhood Development Street
Design Guidelines. Institute of Traffic Engineers, Publication No. RP-027A.
Available from www.ite.org.
Institute of Traffic Engineers (ITE). 2001. Residential Streets, Third Edition. Institute of
Traffic Engineers, Publication No. LP-630. Available from www.ite.org.
LID WORKBOOK: A PRACTITIONER’S GUIDE
5-4
Land Choices. http://www.landchoices.org/. A national non-profit organization promoting land preservation choices. LandChoices is working to reach landowners
and provide them with land preservation choices BEFORE they make that fateful
decision to subdivide their land for conventional subdivision development.
Litman, Todd Alexander. 2004. The Economic Value of Walkability. Victoria Transport Policy Institute. Victoria, British Columbia. Available from http://www.vtpi.org/walkability.pdf.
Low Impact Development (LID) Center website:
http://www.lowimpactdevelopment.org/.
Maine Department of Environmental Protection. 1998. The Buffer Handbook: A Guide to
Creating Vegetated Buffers for Lakefront Properties. Maine DEP. Augusta, ME. Available from http://www.state.me.us/dep/blwq/doclake/publake.htm.
Massachusetts Executive Office of Environmental Affairs (EOEA). 2005. Smart Growth
Toolkit. Boston, MA. Available from http://www.mass.gov/envir/.
Massachusetts Office of Coastal Zone Management (CZM). http://www.mass.gov/czm/. CZM is a founding Green Neighborhoods Alliance member and has actively promoted open space residential design along the coast and in coastal watershed
communities.
Metropolitan Area Planning Council (MAPC). 2005. Massachusetts Low Impact
Development Toolkit Fact Sheets. Metropolitan Area Planning Council. Boston, MA. Available from www.mapc.org/lid.
Metropolitan District Commission (MDC). http://www.mass.gov/dcr/rec-act.htm. MDC
recently produced a publication on "Growth Management Tools: A Summary for
Planning Boards in Massachusetts". It's a concise compilation of the various tools that
Planning Boards have available to them.
MPCA. 1989. Best Management Practices for Minnesota. Minnesota Pollution Control Agency. Minneapolis, MN.
Municipal Research and Services Center for Washington.
http://www.mrsc.org/Subjects/planning/transdev.aspx. - Transit-Supportive Site
Design and Density - a list of resources.
National Center for Transit Research, University of South Florida.
http://www.nctr.usf.edu/pdf/473-135.pdf. - Building Transit Oriented Development in
Established Communities
Natural Lands Trust. http://www.natlands.org/. A Pennsylvania based land trust
organization that has promoted Open Space Residential Design or Conservation Subdivision design in and around Philadelphia. Click on "Planning" then on
"Growing Greener."
LID WORKBOOK: A PRACTITIONER’S GUIDE
5-5
Pinkham, Richard. Nov/Dec 2001. Daylighting: New Life for Buried Streams. Article from Stormwater Magazine Vol. 2, No. 6. Forester Communications. Caledonia, MI.
Available from www.stormh2o.com.
Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies:
An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov.
Rhode Island Department of Environmental Management. January 2005. The Urban
Environmental Design Manual. Rhode Island Department of Environmental
Management, Providence, Rhode Island. Available from
http://www.dem.state.ri.us/programs/bpoladm/suswshed/pubs.htm.
Schueler, T. 1995. Site Planning for Urban Stream Protection. Prepared for: Metropolitan Washington Council of Governments. Washington, DC. Center for
Watershed Protection, Ellicott City, MD. Available from www.cwp.org.
Smart Growth Website. www.epa.gov/ebtpages/envismartgrowth.html. Environmental
Protection Agency (EPA) site on smart growth including a focus on community based approaches to reducing sprawl. Stormwater Manager’s Resource Center, http://www.stormwatercenter.net/. Center for Watershed Protection's Stormwater
Center - A technical clearinghouse for stormwater practitioners and US local
government officials.
Transit Cooperative Research Program. http://gulliver.trb.org/publications/tcrp/tcrp_lrd_12.pdf. - The Zoning and Real Estate Implications of Transit-Oriented Development
Transit-Oriented Development and Joint Development in the United States:
http://gulliver.trb.org/publications/tcrp/tcrp_rrd_52.pdf. A Literature Review
U.S. Environmental Protection Agency. 1999. Parking Alternatives: Making Way for
Urban Infill and Brownfields Redevelopment. U.S. EPA Urban and Economic Development Division. Washington, D.C. Available from
http://www.epa.gov/smartgrowth/publications.htm#articles.
University of Michigan study finds homebuyers want view of woods, not large lawns.
www.umich.edu/news/index.html?Releases/2004/Jun04/r062904a
Urban Land Institute (ULI). 1992. Density by Design. James W. Wetling and Lloyd W.
Bookout, editors. Urban Land Institute, Washington, DC.
UW Center for Urban Water Resources, http://depts.washington.edu/cuwrm/.
Victoria Transport Policy Institute. http://www.vtpi.org/tdm/tdm45.htm. - Using Public
Transit to Create More Accessible and Livable Neighborhoods
Website for Walkable Communities, Inc. www.walkablecommunities.org.
LID WORKBOOK: A PRACTITIONER’S GUIDE
5-6
Wastewater Resources
A Homeowner’s Guide to Septic Systems, U. S. Environmental Protection Agency, EPA-
832-B-02-005, 2002. The information provided in the booklet is intended to help
homeowners understand the function and maintenance of their septic system.
Buzzards Bay Project, Final comprehensive conservation management plan, August 1991. This plan contains recommendations for limiting nitrogen input into the
Buzzards Bay estuarine system.
Cantor and Knox. 1986. Septic system effects on ground water quality. This report focuses
on the various contaminants within septic system effluent and what effects those
contaminants have on ground water quality.
Design Manual – Onsite Wastewater Treatment and Disposal Systems, U. S.
Environmental Protection Agency, EPA 625/1-80-012, 1980. This design manual
provides basic technical information on generic types of onsite wastewater treatment
and disposal systems and should be used as a reference document in conjunction with
the current manual (see item 10).
Environmental Planning for Small Communities – A Guide for Local Decision-Makers,
U. S. Environmental Protection Agency, EPA/625/R-94/009, 1994. This book
outlines a process for developing a community environmental plan.
Hall, M.W. 1975. A conceptual model of nutrient transport in subsurface soil systems, in
Water pollution control in low density areas, University Press of New England. This reference discusses the movement of nitrogen in the subsurface.
Horsley & Witten, Inc., 1998. Coastal resource management and protection workbook.
This workbook presents a variety of challenges in managing and protecting coastal
resources.
Large Capacity Cesspools, Memo from Hawaii DOH, August 13, 2004. This memo explains the conflicts between Chapter 11-62 and the U.S. EPA’s UIC regulations,
and what the state is doing to resolve the conflict.
Nielson, B. 1981. The consequences of nutrient enrichment in estuaries, Eutrophication
Program Report, U.S. EPA Chesapeake Bay Program, Grant No. R-806-189-010. This
report discusses the negative results of excessive nitrogen inputs into an estuarine system.
Onsite Wastewater Treatment Systems Manual, U. S. Environmental Protection Agency,
EPA/625/R-00/008, 2002. This manual was developed to provide supplemental and
new information for wastewater treatment professionals in both the public and private
sectors and covers recent developments in treatment technologies, system design, and
long-term system management.
LID WORKBOOK: A PRACTITIONER’S GUIDE
5-7
Voluntary National Guidelines for Management of Onsite and Clustered (Decentralized) Wastewater Treatment Systems, U. S. Environmental Protection Agency, EPA 832-
B-03-001, 2003. The purpose of the Management Guidelines is to improve the level
of performance of decentralized wastewater treatment systems nationally by raising
the quality of management programs, establishing minimum levels of activity, and institutionalizing the concept of management.
Wastewater Treatment Programs Serving Small Communities, U. S. Environmental
Protection Agency, EPA 832-R-02-004, 2002. This brochure provides a brief
overview of EPA and EPA-sponsored programs that provide assistance on wastewater
issues to small communities.
Wetzel, R.G. 1983. Limnology, Saunders Co., USA, pp. 767. This textbook mentions the role of nitrogen in algal blooms within coastal waters.
Weyer, P. J. Cerhan, B. Kross, G. Hallberg, J. Kantamneni, G. Breuer, M. Jones, W.
Zheng, C. Lynch. 2001. Municipal drinking water nitrate level and cancer risk in
older women: the Iowa women’s health study, in Epidemiology, 12(3):327-338, May 2001. This article discusses the risks of nitrates in drinking water as they relate to bladder cancer.
Yates, M.V. 1987. Septic tank siting to minimize the contamination of groundwater by
microorganisms, U.S. Environmental Protection Agency pub. # 440/6-87-007, 87p.
This reference contains detail on how long viruses can survive in groundwater.