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Geological Tecknies PW, Pace 12 Site Conceptual Model Project No. 989.2 December 17,2003 ' • The subsurface is dominantly fine grained, impeding migration • The structures are a significant distance from the source of the plume 1 6.0 POTENTIAL RECEPTORS ' A sensitive receptor survey was conducted in the third quarter of 2002. Discussion, tables and maps are included in GTI's: Receptor Survey — October 15, 2002. The city of Stockton ' has a population of±225,300 people. GTI personnel mobilized to the Valley Wholesale Drug Company site at 1401 West Fremont ' Street, Stockton, California, on August 1, 2002. GTI personnel, searching for evidence of production, domestic and monitoring wells, walked a 500-foot radius around the site. No evidence of pressure tanks, pumps or pump houses were observed in residences and businesses in the search area. The Stockton Deep Water Channel is located at the southern end of the 500-foot search radius. The Stockton Deep Water Channel and the Mormon Slough are receptors located within. a 2000-foot radius of the site. The physical search was extended to a 2,000-foot radius surrounding the site. GTI personnel investigated this area by driving the streets within the search area and walking the area ' looking for evidence of existing wells. No evidence of domestic, city or production wells was observed during the investigation. Metered water boxes were located along sidewalks and alleyways within the search area, indicating the residents in the search area received a ' municipal water supply. ' 7.0 FINDINGS AND DISCUSSION ' 1. The source of the release has been removed and there is no potential source of contamination remaining at the site. 2. The site has been adequately characterized and the plume boundary is effectively defined. ' 3. The plume has reached a stable state and natural attenuation of contamination is apparent. 4. There are no domestic wells within a 2000-foot radius of the site. Domestic wells beyond this radius are at such a depth that impact is highly unlikely. ' 5. Soil samples collected during the installation of monitoring wells appear to indicate the presence of petroleum hydrocarbons released from the former UST. These concentrations have decreased dramatically since work began at the site. The best example of the reduction in soil contamination can be observed by comparing soil samples at 11 feet bgs from MW-1 (analyzed in 1995) with samples from MW-101 (analyzed in 2002).