SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected EnvironmentSurface Water QualityThere are several unnamed intermittent streams on DMR. HDOH classifies these streams as Class 2.Class 2 waters are protected for recreational uses, aquatic life, agricultural and industrial water supplies,and shipping and navigation. No sampling of surface water quality has been performed atDMR.Groundwater OccurrenceDMR is located in the Mokuleia hydrologic unit of the north hydrologic sector. The State of HawaiiWater Commission estimates the sustainable yield of the Mokuleia hydrologic unit to be 12 mgd. Thecoastal plain is the area where the basal groundwater lens beneath the islands meets the sea and isfound at shallow depths. It is also the area where surface water and shallow groundwater in intermittentdrainages discharge to the sea. Due to its proximity to the coast, the basal groundwater is vulnerableto salt water intrusion. In the coastal area, tidal fluctuations and variations in groundwater dischargecreate a mixing zone in which the groundwater tends to be brackish.Stearns and Vaksvik (1935) mapped the coastal area from Waialua to near Kaena Point as an area ofartesian groundwater (basal groundwater under confining pressure). They attributed the artesian conditionsto the presence of a cap of Koolau basalt over permeable beds in the Waianae volcanic series(Stearns and Vaksvik 1935). Further inland however, the basal groundwater is not artesian (not confinedunder pressure). DMR appears to overlie both of these regions (USAG-HI 2004).Several wells have been installed on DMR, and many of them are present on the ranchlands to theeast of DMR (Hawaii Department of Land and Natural Resources [HDLNR] 2002). Existing water allocationpermits in the Mokuleia aquifer system total 6.3 mgd, or about 52 percent of the sustainableyield of the aquifer system. The water supply for DMR and several nearby residences is a well locatedabout 700 feet south of the control tower. The well reportedly yields about 55,000 gallons perday (gpd) and is completed at a depth of 180 feet (USARHAW and 25th ID [L] 1997).Groundwater QualityNo specific information about groundwater quality at DMR is available. The installation is locatedover an area underlain by caprock, with surficial deposits of dune and beach sands and soils derivedfrom erosion of the nearby Waianae Range. It is expected that basal groundwater beneath the caprockis of good quality because there are no obvious sources of pollutants in the Waianae Range inland ofthe installation. Shallow groundwater may be affected by local sources of pollutants, including agriculturalrunoff and surface spill; however, no data are available to suggest that there has been any historicalimpact on groundwater quality.3.1.2.3 Kahuku Training Area and Kawailoa Training AreaSurface Water OccurrenceAverage annual rainfall within KTA and KLOA ranges from 40 to 50 inches near the coast to150 inches at the summit of the Koolau Mountains. KTA contains portions of four watersheds: Paumalu,Kawela, Oio, and Malaekahana watersheds. The Paumalu watershed in the west includes drainagesfrom Paumalu Stream on the west to Waialee Gulch on the east. The headwaters of the PaumaluStream are in the Pupukea Paumalu Forest Reserve, most of which is within the boundaries of KTA.KTA does not include the downstream portion of the Paumalu Stream, but most of the watershed eastof the Paumalu drainage, almost to the Kamehameha Highway, is on KTA.February 2008 3–24 2/25th SBCT Final EIS