Koholalele Hamakua EA PBR Final TMK No. 4-2-005:001

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HAMAI<UA LAND SALE: I<OHOLALELE FINAL ENVIRONMENTAL ASSESSMENT 3.5 GROUNDWATER RESOURCES AND HYDROLOGY The Site is located within the Pa`auilo aquifer system, which is a component of the East Mauna Kea Aquifer Sector (see Figure 12, Aquifers). The Pa`auilo aquifer system has a sustainable yield of approximately 60 million gallons per day (mgd). Other aquifer systems within the East Mauna Kea Aquifer Sector include the Honoka`a, Hakalau, and Onomea systems. The total sustainable yield of the East Mauna Kea Sector is 388 mgd. Existing water use within the East Mauna Kea Sector is 12.4 mgd, of which agriculture is the largest user at 9.56 mgd (77 %). Of the agricultural use, the average flow of the Lower Hamakua Ditch is estimated at 6.5 mgd in 2003. The ditch system consists of five scattered reservoirs and 14 miles of ditch generally parallel to Mamalahoa Highway from the Kukuihaele Weir to the Pa`auilo Reservoir north of the Site. The potential groundwater withdrawal from the Pa`auilo aquifer system from existing wells based on installed pump capacities is 6.77 mgd, or 11% of the sustainable yield (Fukunaga & Associates, Inc. December 2006). Potential Impacts and Mitigation Measures Since the Site is not within the Hamakua Ditch service area or near known springs, future agricultural use would need to rely on rainfall. Private wells or stream diversions are not likely to be feasible. The availability of potable water for farm dwellings is discussed in Section 5.2 on water infrastructure. 3.6 NATURAL HAZARDS Lava Flow. The U.S. Geological Survey (USGS) has developed lava -flow hazard zones with a numerical rating of 1 to 9, with 1 having the greatest risk. The Site is within Lava -Flow Hazard Zone 8, which indicates that only a few percent of this area has been covered by lava in the past 10,000 years (USGS, 1992). Hurricane. The State of Hawaii has been affected twice in the past two decades by devastating hurricanes — Hurricane `Iwa, in 1982, and Hurricane `Iniki in 1992. Honoka`a High School, located approximately 5 miles east of the project site, is a designated hurricane -proof Emergency Evacuation Center for the area (State Civil Defense, 2007). Earthquake. The most recent series of earthquakes, with magnitudes of 6.7 and 6.0, occurred at Kiholo Bay on October 15, 2006. The soils within the Site are not particularly susceptible to liquefaction that would require special structural measures to mitigate earthquake damage. Flooding. According to the Flood Insurance Rate Map (FIRM), the project site is designated as Zone X, outside of the 500 -year floodplain (Figure 6). Tsunami and Hurricane Surge. Hawaii Island has been affected by tsunami. Most notably, Hilo Bay and the Hamakua Coast suffered extensive damage from the tsunami of 1946. The Koholalele site is located approximately a mile from the shoreline at a ground elevation of 800+ feet, thus it is outside of the tsunami evacuation area. 3-13