SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected Environmenttaminated by TCE. The contamination is being addressed by treating the water pumped by wells atthe wellhead.No groundwater quality data are available for the SRAA. Several wells have been installed and arebeing monitored in the Kunia area, south of the SRAA, as part of a remedial investigation of the DelMonte Corporation Superfund Site. The primary contaminants of concern at this site are pesticides resultingfrom accidental spills. Monitoring wells in this area are also periodically sampled as part ofthe SBMR groundwater-monitoring program. Carbon tetrachloride, a known groundwater contaminantin the area, has not been detected in these wells. TCE, another known groundwater contaminant,has been detected in these wells, but at concentrations below the USEPA Region IX maximum contaminantlevel (MVCL).The Army has started an assessment of offsite potential for contaminants at SBMP under ORAP.While still in the early stages of the assessment, preliminary results show no contamination ofgroundwater by explosive residues.3.1.2.2 Dillingham Military ReservationSurface Water OccurrenceDMR is on the windward (north) coast of the Waianae Range. The average annual precipitation atDMR ranges from 20 to 30 inches but varies with elevation and time of year (USARHAW and 25 thID [L] 2001a). The majority of DMR is located in the Kawaihapai watershed. The extreme easternportion of DMR is located in the Pahole Watershed. Dillingham Trail is located in the Kawaihapai,Pahole, and Makaleha watersheds. Several unnamed intermittent streams occur on DMR.DMR and most of the proposed Dillingham Trail are on the north slope or at the foot of Kaala Mountainand the northwest-trending ridge of the Waianae Range. Streams are incised in steep, narrow valleyscontaining thin soil cover. Most of the streams carry intermittent flows and are subject to shortduration flash floods following rainfall events. However, the lower reaches of some of the streams,where they encounter the alluvial deposits overlying caprock on the coastal plain, flow year round.Stearns and Vaksvik (1935) noted that springs occur in many places along the northeast coast, includingat Waialua, near sea level. They concluded that the springs discharge water mainly from the basalwater table within the Koolau basalts. DMR and Dillingham Trail are underlain by Waianae volcanicsor, on the coastal plain, by sedimentary caprock.FloodingA review of FEMA FIRMS indicates that the northeastern corner of DMR is mapped as a 100-yearflood zone (FEMA 2000). The FEMA study area did not extend over the entire reservation. However,by comparing elevations on the unmapped portion of the reservation to the areas that were mapped, itappears that the 100-year flood zone extends inland from the shoreline to about the 15- to 20-foot elevationcontour. Thus, much of the flat-lying area of DMR may be effectively within an area subject toa 100-year return period for flooding.At least part of the flood potential is likely the result of calculations of tsunami runup. Since 1946, sixtsunamis were recorded in the Hawaiian Islands that had wave runups of 6.6 feet or more (NationalOceanic and Atmospheric Administration [NOAA] 2003). Tsunami evacuation maps prepared by theUS Pacific Disaster Center (PDC) indicate that the flightline at DMR is within the area to be evacuated,roughly 500 feet inland from Farrington Highway (PDC 2001).February 2008 3–23 2/25th SBCT Final EIS