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II. SITE ASSESSMENT SUMMARY A. ASSESSMENT HISTORY The following document describes the history, extent of impact, and prescribed remedial actions for hydrocarbon concentrations at the Former Canteen Facility located just east of Highway 99,between Waterloo Road (Highway 88) and Fremont Street (Highway 26) The one-acre property is zoned for manufacturing and light industrial use,there are no residences in the immediate area The project site and associated operations are expected to remain commercial The site is located in Section 31, T 2N , R 7E , M B B &M , on a portion of Section 54 Weber Grant, San Joaquin County, California (Figures 1 and 2) Site assessment activities include UST excavation activities conducted in March and November 1992 From February 1993 through May 1999 a total of eight (8) soil borings and 13 monitoring wells were drilled and installed at the site and surrounding vicinity The level and extent of hydrocarbon concentrations at the project site are described in the following sections The sections have been organized by which media is impacted B. SITE GEOLOGY & HYDROCARBON CONCENTRATIONS — SOIL The soil stratigraphy across the site is depicted utilizing geologic cross-sections locations as indicated on Figure 3 Cross-Section A-A' (Figure 4) extends from monitoring wells MW-6 to MW-9 (north to south) and Cross-Section B-B' (Figure 5) extends from monitoring wells MW-7 to MW-1 (southwest to northeast) Both cross-sections include wells screened in the shallow and deep aquifers In general, shallow subsurface soil at the site consists of interbedded units of fine-grained (silt) deposits and coarse-grained (sand) deposits Based on the soil boring logs, relatively fine- grained soil consisting of silt and clay was encountered from the ground surface to approximately 60 feet below ground surface (bgs) These fine-grained soils appeared to be underlain primarily by deposits consisting of clayey to silty sand and sand to a depth of approximately 116 feet bgs A stiff silt layer was encountered from about 116 to 118 feet bgs The silt layer was underlain by silty sand and sand Soil boring and monitoring well construction details are presented in Appendix A Concentrations of sorbed-phase hydrocarbons detected in the soil were compared to the EPA Region 9 PRGs The soil samples collected from the south and southeast walls of the UST excavation (14 to 19 feet bgs) exceeded the Industrial PRGs for benzene, toluene, and xylenes The benzene PRG was also exceeded in borings SB-2 and SB-13D (46 5 feet bgs) The TPH-G concentrations detected in these soil samples vaned from 10 3 to 17,600 mg/kg The location of soil borings installed at the site and analytical results are presented on Figure 6 II-1