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Former Countryside Market,Stockton, California Feasibility Study and Interim Remedial Action Plan May 20,2013 2.0 SITE BACKGROUND AND PHYSICAL SETTING The following sections present a discussion of the Site background and phy ical setting. 2.1 Site Location and Description The City of Stockton is centrally located in San Joaquin County in the north end of the San Joaquin Valley. The Site is located in eastern San Joaquin County, approximately two miles east of the city limits of Stockton, and southeast of the intersection of Copperopolis Road and Tulsa Road. The Site vicinity is primarily a rural residential and agricultural area. The Site is vacant, with the current owner occupying a single-family residence on a separate parcel of land irectly south of the Site. Countryside Market, a former gasoline service station and convenience tore, occupied the property until approximately 1993. The property has been vacant since early 1993 2.2 Site Geology/Hydrogeology The Site (Figure 2) lies approximately six miles east of Stockton's city center at an elevation of 52 feet above mea sea level. Results from prior investigations indicate fine alluvial sediments consisting of predominantly sandy clay and clayey sand are present at the Site and surrounding area to depths of approximately 105 feet below ground surface (bgs), with relatively coarser grained lithologies interbedded at depths ranging from approximately 65 to 105 feet bgs. Boring logs for all of the existing monitoring wells(MW-1 through MW-7), and soil borings SBA and SB-2, are provided 3s Appendix A. Groundwater was initially encountered at approximately 92.5 to 93 feet bgs during drilling activities, and has ranged from approximately 88.5 to 94.5 feet below top of casing (ft-toc) since J nuary 2012. The available elevation and potentiometric surface data indicates that groundwater gen;rally flows in a northeastern direction at a gradient of approximately 0.003 feet per foot (ft/ft), which is consistent with historic conditions. 2.3 Previous Site Investigations In March 1993, Stockton Service Equipment Company removed two ,000-gallon leaded-gasoline underground storage tanks (USTs) from the property. Four soil samples (TK1N, TK1S, TK2N, and TK2S) were collected from beneath the USTs at depths of approximately 7.5 feet bgs. The samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg), ben Earle, toluene, ethylbenzene, and xylenes (BTEX compounds), ethylene dibromide (EDB), and total lec d. TPHg was detected in all four samples at concentrations ranging from 770 to 6,500 milligrams per kilogram (mg/kg). The excavated soil was subsequently returned to the excavation, and no investigation was performed (UEC, 2001). In October 1995, approximately 40 cubic yards of hydrocarbon-imps ed soil was excavated and replaced with clean backfill. The former UST pit was excavated to 11 end 13 feet bgs. Soil sample CM-1-13 collected from the bottom of the excavation indicated TPHg, benzene, toluene, Feuibilq 5"&IRAP Te#Fnal. o 2-1 The Source Group,Inc.