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r L� 2 San Joaquin County Environmental Health Department ATC March 6,2013 Shaping the Future Smith Technology supervised the installation of three groundwater monitoring wells, MW-1, MW-2, and MW-3 on July 18, 1995. These wells were installed to facilitate groundwater monitoring and sampling at the site. Initial analytical results indicated the presence of elevated concentrations of petroleum hydrocarbons down gradient of the former gasoline USTs. Nine soil borings were advanced to depths up to 15 feet below ground surface(bgs) on September 24 and October 2, 1996. Analytical results of the soil and groundwater samples indicated the general extent of petroleum hydrocarbons and fuel oxygenates in soil and groundwater beneath the site. Soil vapor analytical results indicated the availability of oxygen,carbon dioxide, nitrogen, and methane in the vadose zone. Geophysical testing results of soil samples from the site indicated that the on-site receptor, the water supply well, would not likely be affected by the petroleum hydrocarbon plume in groundwater within the next 20 years, in the worst case. Three additional groundwater monitoring wells(MW-4, MW-5, and MW-6)were installed at the site on March 9, 1999. Analytical results of the soil and groundwater samples collected at the site indicated the lateral extent of impacted soil and groundwater had been defined. At the request of the San Joaquin County Environmental Health Department(SJCEHD),ATC evaluated contaminant migration potential of hydrocarbon affected soil and groundwater at the site using the EPA's BIOSCREEN (v.1.4) software program. The results of the computer modeling indicated the petroleum impacted soil and groundwater at the site do not appear to be an immediate and significant threat to human health or the environment.The computer modeling results are presented in ATC's Addendum to Additional Site Evaluation and Request for No Further Action for Fayette Manufacturing Corporation, dated November 4, 2002. On April 5 and 8, 2004, an additional subsurface investigation consisting of four soil borings(GP-1, GP-2, GP-3, and CPT-1)was conducted to evaluate the vertical extent of impacted soil in the vicinity of the former USTs and possible lateral migration of impacted groundwater between wells MW-4 and MW-5. Analytical results confirmed that dissolved phase petroleum hydrocarbons had migrated between wells MW-4 and MW-5. Groundwater monitoring wells MW-7 and MW-8 were installed at the site on January 10 and 17, 2005. These wells were installed to provide lateral definition of the impacted groundwater plume down-gradient from former USTs. Six additional soil borings(GP-4 through GP-9)were advanced at the site to provide source area characterization and fill data gaps down-gradient from the identified source area on September 13,2007. Analytical results confirmed that elevated concentrations of petroleum hydrocarbons remain in soil and groundwater beneath the site. Two in-situ soil vapor probes(VP-1 and VP-2)were advanced to collect soil vapor for laboratory analyses on September 14, 2007. Analytes detected in the soil vapor samples exceeded a hazard index of 1.0 (estimated site value of 1.6),the one-in one-million (1.OE-06)excess cancer risk for residential receptors(estimated site value of 1.79E-04), and the one-in-one hundred-thousand (1.OE-05)excess cancer risk for commercial receptors(estimated site value of 1.79E-04). As a result, recommendations were provided to implement a remedial plan at the site. ATC supervised the installation of groundwater monitoring well MW-9, three dual phase extraction wells(DP1 through DP3), and two air sparge wells(AS1 and AS2) between August 31 and September 2, 2009. The wells were installed to facilitate remediation pilot testing activities at the site. Pilot testing activities that included high vacuum dual phase extraction (HVDPE) and air sparging combined with soil vapor extraction(AS/SVE)between January 19 and August 19, 2010. In April 2012, SJCEHD requested that ATC reevaluate the soil vapor risk calculations for the site. Results of the revised risk assessment led SJCEHD to direct that further evaluation of soil vapor risks be performed at the site. www.cardnoatc.com