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Work For Additional Assessment and Feasir>�y Study ` Quik Stop Market No. 132 3555 West Hammer Lane Stockton, California On April 29, 1992, RESNA Industries Inc. (RESNA) completed a Shallow Soil Gas and Groundwater Survey around the Taco Bell property adjacent to the site. Tracer Research Corporation of Tucson, Arizona was subcontracted to perform the survey. A % inch diameter probe was advanced to depths as deep as 20 feet bgs at ten locations along the south and east sides of the Taco Bell property. A total of seven soil gas and six groundwater samples were collected from the holes. Very low concentrations of petroleum hydrocarbons were detected in three soil gas samples and two groundwater samples. Based on resistance during advancement, it was concluded that at depths of 8 to 14 feet bgs, a dense less porous soil is present. On December 9, 1992, RESNA completed an additional site assessment consisting of the installation of two additional off-site groundwater monitoring wells (MW-6 and MW-7). The soil and groundwater samples (from new and existing groundwater monitoring wells) were analyzed for TPHg and.BTEX in accordance with EPA test methods 8015 and 8020, respectively. TPHg and BTEX were not present in any of the soil borings. , TPHg was present in a groundwater sample obtained from MW-5 (350 µg /L). BTEX (at least one constituent) was present in groundwater samples obtained from MW-2 and MW-5. The maximum benzene concentration was 0.66 gg/L in the groundwater sample obtained from groundwater monitoring well MW-2. The locations of groundwater monitoring wells are shown on Figure 2. In March 1996, groundwater samples obtained from groundwater monitoring wells MW-1R, MW-2, MW-5, MW-6 and MW-7 were first analyzed for methyl tert-butyl ether (MTBE) in accordance with EPA test method 8020. MTBE was present in groundwater samples obtained from MW-1R, MW-2 and MW-S. The maximum MTBE concentration was present in a groundwater sample obtained from MW-5 (1,100 pg/L). MTBE concentrations in MW-5 subsequently decreased steadily for five quarters until September 1997, when the MTBE concentrations rose back to 1,100 gg/L. In a letter to Quik Stop Markets Inc., dated April 1, 1997, the San Joaquin County Public Health Services Environmental Health Division (SJCPHS-EHD) stated that "the only remaining issue at the site is the MTBE currently being detected in Monitoring Well MW-5", The SJCPHS-EHD recommended the sampling of only Monitoring Well MW-5 for future quarterly monitoring events, therefore, no other groundwater monitoring wells at the site were sampled during the first quarter 1998 sampling event. However, in a letter to Quik Stop Markets Inc. dated April 27, 1998, the SJCPHS-EHD requested that "each quarter sample and analyze water from all of the MWs until further direction from the San Joaquin County Public Health Services Environmental Health Division". A Workplan for additional groundwater investigation dated October 19, 1998 was prepared by ATC at the request of the SJCPHS-EH. The Workplan included a well survey and an operating history of the site USTs. The well survey was conducted to locate any domestic, municipal, and agricultural wells within 2,000 feet of Quik Stop No. 132. No drinking water wells were identified within the search radius. Two irrigation wells were identified within 2,000 feet of Quik Stop 132. The operating history of the site USTs includes installation of new double-walled USTs and product lines, dispensers, and canopies in March 1991 (ATC, October 1998).