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Work Plan for Soil and Groundwater vestigation ECOR Former ARCO Service Station#0760 December 13,2006 Page 2 hydrocarbons remain beneath the USTs, waste oil tank cavity, product delivery lines, and dispenser islands. No volatile organic compounds (VOCs)were detected in any of the soil samples collected around the waste oil tanks. The highest soil concentrations of residual petroleum hydrocarbons appear to exist in the northern portion of the dispenser islands and near the northern most waste oil tank from 20 to 40 feet below ground surface (bgs). In June 1991, RESNA conducted an SVE pilot test using three on-site vapor extraction wells (VW-1, VW-2, and VW-3). Vacuums of 4.5 to 6 inches of water column were applied to the wells. Based on well head vacuums ranging from 4.5 to 6 inches of water column, and an average flow rate of 35 actual cubic feet per minute,the effective radius of influence(ROI)forthese wells was estimated at 22 feet. As part of divestment activities, URS Corporation (URS) supervised the excavation of all USTs, dispenser, and associated product piping at the site. Initial soil sampling indicated the presence of petroleum hydrocarbons,therefore,over-excavation was performed. Analytical results of groundwater samples collected from three on site monitoring wells between October 2002 and July 2003 identified the presence of 1,2-dichloroethane (1,2-DCA)at the site. On March 22 and 23, 2004, phase I of a two phase site assessment was conducted. Three off-site vertical soil borings(B-25, B-26,and B-27)were advanced by URS Corporation(URS)to a depth of 65 feet below ground surface(bgs),and depth-discrete soil and grab groundwater samples were collected to assess the western and southern lateral extent of 1,2-DCA in groundwater beneath the site. Analytical data from the March 2004 investigation determined that the western extent of 1,2-DCA- impacted groundwater was not yet defined and that more sampling would be required during the second phase of the assessment. In addition, in its letter dated October 14,2004,SJCEHD reaffirmed its interest in defining/monitoring the eastern extent of impacted groundwater between the site and City of Lodi municipal well #1 R (812 feet east of the site). Between November 20,2004,and November 30,2004, URS conducted the following field activities as part of phase II of the assessment: • One vertical soil boring (B-28) was advanced to first encountered groundwater on the northern side of Lodi Avenue, approximately 180 feet west of the site, and depth-discrete soil samples and a grab groundwater sample were collected to define the western extent of 1,2-DCA-impacted groundwater. • One vertical soil boring was advanced to 70 feet bgs on the eastern side of S. Cherokee Lane, and a 2-inch diameter monitoring well (MW-4) was installed to monitor the eastern extent of impacted groundwater between the site and the City of Lodi municipal well. • One vertical soil boring was advanced to 105 feet bgs onsite and a 2-inch diameter deep groundwater monitoring well (MW-5)was installed in the area reporting the highest 1,2-DCA concentration to assess the vertical extent of impacted groundwater. The Phase II did not identify any petroleum contamination in the soil samples, grab groundwater sample,or the groundwater sample from MW-4. The groundwater sample collected from MW-5 only identified toluene (0.55pg/L) and total xylenes (0.84 pg/L)at or above the method detection limits. This investigation resulted in establishment of vertical and horizontal extent of contamination at this site. ARCO 00760 Soil and Groundwater Investigation WP.doc