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i 5.0 Beneficial Uses of Water The Water Quality Control Plan (Basin Plan) for the San Joaquin River Basin lists the beneficial uses of groundwater within San Joaquin County as municipal and domestic water supply, irrigation, stock watering and service supply (RWQCB, 1990) Groundwater is known to be used for agricultural purposes throughout the rural area surrounding the site The nearest known groundwater wells are located approximately 2,000 feet east and northeast of the site San Joaquin County, as well as state records, indicates that groundwater flows northeastward beneath the site and occurs at about 40-50 feet below the surface 6.0 Extent of Petroleum Hydrocarbons in Soils 6.1 Summary of Basement Area Soil Sample Analytical Data In June 1990, two diesel UST's (300 gallons and 550 gallons) located beneath the on-site building were closed in place by removing all product, triple rinsing, pumping of rinsate, and filling with cement slurry Four soil borings (SSI, SS2, SS3, and SS4) were hand bored beneath the building near the abandoned tanks Soil bonngs SSI and SS4 were bored near the south (fill) and northeast ends of the 550 gallon tank Analysis of soil samples collected at 7 5 feet and 10.5 feet below the basement floor (bbf) from boring SSI, revealed diesel concentrations of 990 ppm and 870 ppm respectively Analysis of soil samples collected from boring SS4 at 7 5 feet and 10 5 feet below the basement floor (bbf) revealed no detectable diesel concentrations Soil borings SS2 and SS3 were bored near the northeast and northwest (fill) ends of the 300- gallon tank Analysis of soil samples collected at 6 9 feet and 9 9 feet bbf revealed diesel concentrations of 13,000 ppm and 12,000 ppm respectively Analysis of soil samples collected from boring SS3 at 8 3 feet and 9 9 feet bbf revealed diesel concentrations of 17,000 ppm and 22,000 ppm. Drilling efforts in July 1994 were positioned so as to examine current soil quality in areas previously observed to contain petroleum hydrocarbon concentrations Recent boreholes VW-1, VW-2 and VW-3 were positioned adjacent to the original boreholes SS2, SSI and SS3 respectively Upon analysis, two of the three samples collected from soil boring VW-1 and one of the two samples collected from boring VW-3 were found to contain detectable volatile petroleum hydrocarbons (BTEX) Total BTEX concentrations ranged from 0 008 ppm to MZ/0406-951UST195-0089 5