HomeMy WebLinkAboutENG_Drywell_Capacity_Verification_Testing
ENGINEERING DIVISION MEMORANDUM
Mitchell D. Roth Mayor
Deanna S. Sako Managing Director
Stephen M. Pause, P.E. Director
Malia Kekai Deputy Director@nuttflJ nf �afuai 'i
DEPARTMENT OF PUBLIC WORKS Aupuni Center 101 Pauahi Street, Suite 7 • Hilo, Hawai'i 96720-4224 (808) 961-8321 • Fax (808) 961-8630public_ works@hawaiicounty.govCounty ofHawai'i is an Equal Opportunity Provider and Employer. To: Public
From: Alan Keane Thompson, P.E.
{j,-/l.(�Date: August29,2024
Subject: Drywell Capacity Verification Testing
The procedures below shall be followed for the capacity verification testing of all newly
installed drywells intended tb control rainfall runoff in the County of Hawaii:
•Upon completion of construction of the drywell, the following steps shall be taken.
Verification testing shall be done in the presence of the Engineer or a representative.
All processes and results shall be documented by the contractor on the attached
form.
o Pretest: Inject a minimum of 2,000 gallons of potable water into the drywell.
o First Test: Within two hours of the completion of the previous step, inject a
minimum of 2,000 gallons of potable water into the drywell at the maximum
flowrate allowable by the equipment used.
■ Record volume, start time of injection, time to complete the injection, and the
time required for the water to fall each of three 24" increments.
■Calculate the rate of infiltration for each 24" increment and the average rate of
infiltration for the three increments combined.
o Second Test: Within two hours of the completion of the previous step, inject a
minimum of 2,000 gallons of potable water into the drywell at the maximum
flowrate allowable by the equipment used.
• Record volume, start time of injection, time to complete the injection, and the
time required for the water to fall each of three 24" increments.
• Calculate the rate of infiltration for each 24" increment and the average rate of
infiltration for the three increments combined.
Average infiltration rates for the measured tests must be within 0.5 cubic feet per
second of each other or a third test must be conducted within two hours of the end of
the second. If a third test is required, the average of the results of the second and
third tests shall be used to determine the capacity of the drywell.
If standing water is observed at the bottom of the drywell and/or the bottom of the
drywell is at or below 10' above Mean Sea Level, an additional 500 gallons of water
must be added to each of the testing quantities and the bottom of the lowest reading
must be at least 24" above the observed standing water level or the bottom of the
drywell, whichever is higher.
County ofHawai'i is an Equal Opportunity Provider and Employer.
Project Name
Date of Test
Drywell Location
Diameter of Drywell
First Injection (Pretest)
Volume
Start Time End Time
Second Injection (First Test)
Volume
Start Time Time to Complete (sec)
Average Injection Rate (gal/sec)
Time to drop first 24" Infiltration Rate ((TTr2x24")/time)
Time to drop second 24"Infiltration Rate ((TTr2x24")/time)
Time to drop third 24" Infiltration Rate ((nr2x24")/time)
Average Infiltration Rate
Third Injection (Second Test)
Volume
Start Time Time to Complete (sec)
Average Injection Rate (gal/sec)
Time to drop first 24" Infiltration Rate ((nr2x24")/time)
Time to drop second 24" Infiltration Rate ((nr2x24")/time)
Time to drop third 24" Infiltration Rate ((nr x24")/time)
Average Infittration Rate
Contractor's Name / Signature
DPW Representative Name / Signature