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(VYATC A S S O C I A T i= S I iV C (DWR) groundwater well construction logs, and conducted a site walk in the vicinity of the site to identify any groundwater wells located within a 2,000-foot radius of the site This survey revealed 14 wells located within approximately 2,000 feet of the site The closest of these wells is located approximately 800 feet upgradient of the project site The receptor survey findings are summarized in ATC's Well Survey for Andrew and Edith Trust, for the Property at 1112 East Harding Way, Stockton, California, dated April 9, 1999 On April 11, 2000, a single soil boring (SB7) was advanced to approximately 65 feet bgs to evaluate whether groundwater had been impacted at the subject site Groundwater was initially encountered at approximately 45 feet bgs and a sample was subsequently collected from the soil boring using a Hydropunch® groundwater-sampling tool In order to determine the vertical extent of contamination in the most cost-effective manner, the soil boring was further advanced to a total completion depth of 66 5 ft bgs where field observations suggested the vertical extent of the petroleum hydrocarbons had been realized Analytical results and field observations indicated that soil and groundwater beneath the location of the former USTs were impacted by residual petroleum hydrocarbon constituents The vertical extent of impacted soil and groundwater appeared to be defined However, the lateral extent of petroleum hydrocarbon constituents at or near the groundwater interface was undefined Additional work to further characterize the extent of contamination was requested by the PHS/EHD in correspondence dated September 20, 2000 • On November 15 and 16, 2001, an ATC geologist supervised the advancement of three soil borings to approximately 54 to 55 feet bgs Soil borings were then completed as groundwater monitoring wells MW1, MW2, and MW3 The soil sample collected from boring MW2 at a depth of 35 5 feet bgs contained the highest concentrations of TPHg, ethyl benzene, and xylenes The soil samples collected from boring MW2 at depths of 30 feet bgs and 55 feet bgs contained only trace concentrations of TPHg, ethyl benzene, and/or xylenes The soil samples collected from borings MW1 and MW3 at depths of 35 feet bgs contained trace concentrations of xylenes and TPHg, respectively The samples collected from borings MW I and MW3 at depths of 40 feet bgs did not contain detectable concentrations of TPHg or BTEX Methyl tertiary butyl ether (MTBE), t-amyl methyl ether (TAME), t-butanol (TBA), ethyl t-butyl ether (ETBE), di-isopropyl ether (DIPE), 1,2- dichloroethane (1,2-DCA), or 1,2-dibromoethane (EDB) were not detected in any soil samples collected from borings MW1, MW2, and MW3, though the detection limits were elevated in the MW2 sample from 35 5 feet bgs due to the high concentrations of TPHg noted previously In July and December 2003, ATC conducted additional subsurface investigation activities at the site that included cone penetration testing, advancing a soil boring (SB8), and installation of monitoring wells MW4 through MW7 Petroleum hydrocarbons were detected in soil samples collected from the boreholes of MW5 and MW6, and in the groundwater samples collected from MW4 through MW7 GROUNDWATER FLOW DIRECTION Groundwater level measurements were collected from monitoring wells MW1 through MW7 on April 9, 2004 Groundwater elevations ranged from --27 19 to —27 26, representing an average • increase in the groundwater table elevation of approximately 2 19 feet since January 2004 The water level data were used to develop the groundwater elevation contour map (Figure 3) Assuming that horizontal isotropic conditions prevail, shallow groundwater beneath the site generally flowed s lenvironmenta11224931Reportsl2QR-04 doc 2