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I..r a i ATC Associates Inc. v 1117 Lone Palm Avenue,Suite 201 Modesto, California 95351 209-579-2221 Fax:209-579-2222 ASSOC IATES I N C . 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 potential impacts to groundwater beneath the 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. To evaluate the vertical extent of contamination, the soil boring was advanced to a total depth of approximately 66.5 feet bgs where field observations suggested the vertical extent of the petroleum hydrocarbons had been assessed. Analytical results and field observations indicated that soil and groundwater beneath the location of the former USTs were impacted by petroleum hydrocarbons. The vertical extent of impacted soil and groundwater appeared to be assessed. However, the lateral extent of petroleum hydrocarbon constituents at or near the groundwater interface was not completely assessed. On November 15 and 16, 2001, an ATC geologist supervised the advancement of three soil borings to depths of approximately 54 to 55 feet bgs. These 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, ethylbenzene, `r and total xylenes. The soil samples collected from boring MW2 at depths of 30 feet bgs and 55 feet bgs contained only trace concentrations of TPHg, ethylbenzene, and/or total xylenes. The soil samples collected from borings MW1 and MW3 at a depth of 35 feet bgs contained trace concentrations of total xylenes and TPHg, respectively. The samples collected from borings MW1 and MW3 at a depth of 40 feet bgs did not contain detectable concentrations of TPHg or BTEX. None of the remaining analytes of interest were detected in the soil samples collected during the advancement and installation of wells MW1, MW2, and MW3. 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 during the advancement and installation of wells MW5 and MW6, and in the groundwater samples collected from wells MW4 through MW7. On November 17 and 18, and December 5 and 28, 2005, an ATC geologist supervised the advancement of five soil borings, S139 through SB13. The borings were advanced for the purposes of evaluating the horizontal extent of petroleum hydrocarbon impacted soil and groundwater in the vicinity of the site. Details of these activities were summarized in ATC's Summary Report of Additional Subsurface Investigation, dated July 12, 2006. Between May 24 and June 8, 2007, an ATC geologist supervised the installation of monitoring wells MW8 through MW11. MW8 and MW11 were installed off-site to the northeast and north adjacent to 1139 and 1107 East Harding Way, respectively, to evaluate the lateral extent of petroleum impacted groundwater downgradient of the subject site. Details of these activities are summarized in ATC's Subsurface Investigation Report, dated November 19, 2007. ATC prepared a Feasibility Study, dated September 12, 2008, which included evaluation of potential remediation options for the site. Enhanced Natural Attenuation for soil remediation and Groundwater Extraction with Biological Treatment and Bio-Enhanced Infiltration for r... s:\environmental\22493\Reports\QMR 2011 SA1.doc 2 V