Marine Corps Base (MCB) Camp Pendleton encompasses about 125,000 acres in southern California (MCB Camp Pendleton 2001a and 2001b; USEPA 2004). The base lies along the Pacific Ocean and contains an estimated 17 miles of coastline (MCB Camp Pendleton 2001a and 2001b). The entire base, except for about 125 acres in southern Orange County, is within northern San Diego County (MCB Camp Pendleton 2001a). MCB Camp Pendleton lies between two major cities—San Diego is 38 miles south of the base and Los Angeles is 82 miles north (MCB Camp Pendleton 2001b).
In 1980, 2, 4, 5-TP (silvex) was detected in two base production wells (51 and 73 micrograms per liter [μg/L]) (MCB Camp Pendleton 1980). An initial assessment study (IAS) conducted in September 1984 identified eight sites that warranted further evaluation. The IAS determined that none of the sites posed an immediate health hazard, but recommended five sites for further investigation (SCS Engineers, Inc. 1984). A site investigation (SI) in 1988 included sampling of six sites: the five identified in the IAS and an additional site recommended for further study by the Navy. Sampling detected metals in soil, groundwater, sediment, and surface water; VOCs in groundwater and surface water; polychlorinated biphenyls (PCBs) and pesticides in soil; and an SVOC in groundwater (CDM 1988).
Three of the remaining UST sites are in residential areas, but only subsurface soil and groundwater contamination remains at these sites. Soil remediation has occurred in these residential areas, with remaining contamination beneath several feet of soil or pavement and inaccessible to residents. Further, the UST site-related groundwater contamination is not near any drinking water production wells (Mark Bonsavage, IRP Manager, MCB Camp Pendleton, personal communication, 2005).
The base water systems draw their water from local groundwater basins. MCB Camp Pendleton has four main groundwater basins: Las Flores, San Mateo, San Onofre, and Santa Margarita (Parsons 1999). The base’s North System has four wells in the San Mateo River Basin and three wells in the San Onofre River Basin (MCB Camp Pendleton 2004a, 2005c). This system provides drinking water to about 12,000–15,000 consumers in the San Onofre housing and mobile home areas, San Onofre Recreation Beach, and 52–64 areas of the base (see Figure 3) (MCB Camp Pendleton 2005b, 2005c). The South System has 12 wells in the Santa Margarita River Basin and three wells in the Las Flores River Basin. This system provides drinking water to about 39,000–43,000 consumers in the remaining base areas, including residences in the 43 area and all areas south (MCB Camp Pendleton 2004a, 2005c).