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ATC Associates Inc. YA 1117 Lone Palm Avenue,Suite Modesto,California 953511 209-5792221 Fax:209-579-2225 j i Site Location The site is located on the northwest corner of East Main Street and South Oro Avenue in Stockton California, as shown on Figure 1. The facility is a commercial and residential area. The site is currently occupied by the Jamar Service Station. Background I i In 1995, one 500-gallon waste oil underground storage tank (UST) and one 500-gallon kerosene UST were removed from the site. In December 1998, two 6,000-gallon and one 10,000-gallon gasoline USTs were removed from the site. Soil samples were collected from the tank pit and analyzed for petroleum hydrocarbons. Lab i analyses indicated the samples collected from the tank pit contained detectable concentrations of petroleum hydrocarbon constituents. The excavation was subsequently backfilled and a 20,000- gallon UST was installed. In September 1999, John P. Cummings & Associates (JPCA) advanced three soil borings (MW1, MW2, and MW3) to depths ranging from approximately 74 to 78 feet below ground surface (bgs). i The borings were completed as groundwater monitoring wells. i In August 2000, JPCA advanced three soil borings (BI, MW4, and MWS); MW4 and MW5 were j completed as groundwater monitoring wells. BI was advanced to a depth of 115 feet bgs and MW4 j and MW5 were installed to a depth of 75 feet bgs. Soil and groundwater samples were collected and analyzed. Site activities were summarized in JPCA's 2"`r Phase II Environmental Assessment Report, dated October 25,2000. In January 2003, GHH Engineering, Inc. (GHH) advanced three cone penetrometer borings and three soil borings to depths ranging from 104 feet bgs to 122 feet bgs. In May 2003, GHH advanced MW6a, MW6b, MW7a, and MW7b to the east of the site. These borings were completed as well clusters with MW6a and MW7a advanced to a depth of approximately 75 feet bgs, and MW6b and MW7b advanced to a depth of approximately 94 feet bgs. GHH also installed EWl in the southeast portion of the site. Site activities were summarized in GHH's Second Quarter 2003 Groundwater Monitoring Report and Additional Assessment Report, dated June 2003. i In January 2004, an ATC geologist supervised the installation of five injection wells (IWI - IW5) associated with an ozone injection system. Each injection well has a shallow and deep spargepoint for the ozone. The shallow spargepoints were installed to a depth of approximately 74.0 feet bgs and the deep spargepoints were installed at a depth of approximately 107.7 feet bgs. i Jamar Service Station 2 j i