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L - ARCADIS Ms. Lori Duncan L March 20,2009 On March 26, 2002, borings P1, P2, P3, and P4 were advanced. The soil samples collected from boring P3 at 40 feet below ground surface(bgs) had total petroleum hydrocarbon as gasoline(TPH-g, also known as TPH-GRO), toluene, ethylbenzene, and total xylenes concentrations of 6,300, 10, 500, 250 and 1,600 milligrams per kilogram (mg/kg), respectively. LrOn November 28, 2005, borings B1 and B2 were advanced. Petroleum hydrocarbon concentrations detected in soil samples collected from borings B1 and B2 were below the California Regional Water Quality Control Board (RWQCB) Environmental L Screening Levels (ESL)for deep soils (RWQCB, 2005). Soil samples collected from 65, 70, 75, and 85 feet bgs in B1 and B2 had no petroleum hydrocarbon detections above the laboratory method detection limits (MDL). 6 L On August 21 2006 one 2 inch outside diameter(OD) polyvinyl chloride((PVC) monitoring well (MW-1)screened from 65 to 85 feet bgs, was installed under the existing canopy. On June 11, 2008 ARCADIS supervised Spectrum Geophysics (Spectrum)during geophysical survey activities used to evaluate probable locations of closed (abandoned in place) USTs or other remaining facilities. An electromagnetic(EM) survey was performed first as a rapid screening tool to identify potential USTs and L other subsurface structures. Results of the EM survey were used to focus . subsequent ground penetrating radar(GPR)survey activities. Upon review of EM-61 L and GPR profiles, no definitive UST-like signatures were observed. Between June 16 and 23, 2008, Cascade Drilling Incorporated (Cascade), under the supervision of ARCADIS, installed four groundwater monitoring wells (MW-2, MW-3, MW-4, and MW-5) and advanced one boring (B-3)to evaluate the potential extent of petroleum hydrocarbon impacts to groundwater near the former UST complex. The 14 soil samples collected had no petroleum hydrocarbons detections above the L laboratory MDLs, with the exception of low detections of ethanol and methanol at 40 feet bgs in groundwater monitoring well MW-3 and boring B-3. Total petroleum hydrocarbons as diesel (TPH-DRO)were detected in groundwater samples collected L . from all five monitoring wells. Given the distribution of similar concentrations across the site, TPH-DRO may be a regional issue in this area of Stockton. 1,2- dichloroethane (1,2-DCA)was detected at a concentration above the California Primary Maximum Contaminant Level (MCL) in the groundwater sample collected rfrom MW-1. Iret Page: 2/7 llamadisus\o icedatalSwmmento-CAIEN\ACHEVRONM907516 Deli"rableslReportsVAwosement AddendumlTex8309075 Site Assessment Addendum Report oc 282910950.d . .