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r V from beneath the gasoline, diesel and waste oil USTs. Soil sample locations were not available for review. 'r' Between 1987 and 1996, seven borings and 21 groundwater monitoring wells were installed at the site to determine the vertical and lateral extent of soil and groundwater impacts. Maximum Lw TPHg, TPHd, and benzene concentrations of 13,000, 1,800, and 4.7 mg/kg,respectively, were detected in the soil samples collected from the soil borings. Historically, TPHg,TPHd, methyl tert-butyl ether (MTBE) and benzene concentrations up to 231,000, 6,100, 96 and 28,000 micrograms per liter(gg/L), respectively, were reported for groundwater samples. +- In July 1994, nine wells were abandoned because they went dry. In September 1998,two wells were removed during construction site activities. Currently, 11 wells are included in the quarterly monitoring program. In 1992, a vapor extraction pilot test was performed at the site with recommendations indicating that soil vapor extraction (SVE) was considered a feasible remediation alternative. In February 1999, URS Greiner Woodward Clyde (URS) conducted a Human Health Risk Assessment (HHRA) and Groundwater Impact Analysis. The HHRH evaluated the potential impacts to groundwater and human health risks due to potential exposure to residual petroleum ` hydrocarbons remaining in the soil and groundwater. During the assessment process, carcinogenic risks and noncarcinogenic hazard indexes were calculated, as well as, potential +-• health risks for each complete exposure pathway and receptor population. Two primary receptor populations were evaluated, occupational on-site and off-site residential. Calculated risk ,,W numbers were below levels of concern for both populations. Site soil concentrations were below the industrial Preliminary Remediation Goals (PRGs) for chemicals of concern. Conservative fate and transport modeling indicated that potential concentrations of chemicals of concern in groundwater would not cause significant impacts to human health. •.. The HHRA reported that the groundwater quality meets the Basin Plan objectives within a distance of approximately 61 m(200 ft) from the original source. The HHRA summarized more than 12 years of groundwater monitoring data that verified both the limited area of affected shallow groundwater and the continued decline in residual concentrations in that limited area. In March 2000, an Additional Groundwater Study was performed to perform discrete vertical groundwater sampling, slug tests, petroleum hydrocarbon mass estimation in soil, and evaluate natural attenuation (URS, 2000). Generally,TPHg and BTEX concentrations in groundwater have decreased in concentration and corresponded with an increase in the groundwater elevation sxnP-N.IsacoPVOOZPRMJ91B W2M2ab.aa 1-2 �oro2n000)