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L � VTC www.atcassociates.com 1.0 INTRODUCTION On behalf of Quik Stop Markets, Inc., ATC Associates, Inc. (ATC) is submitting a Case Closure Summary for Quik Stop Market No. 132, located at 3555 West Hammer Lane, Stockton, California (Site). This Case Closure Summary is based on a request by the San Joaquin County Environmental Health Department(SJCEHD) in their letter dated March 8, 2011 (attached as Appendix A). This Case Closure Summary presents historical and current Site �. data and discusses items detailed in Section 6.0 of the Tri-Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of Underground Tank Sites (2004, Central Valley Regional Water Quality Control). In ATC's professional opinion, this Site should be considered for no further action required based on the information provided herein. 2.0 SITE BACKGROUND v Quik Stop Market No. 132 is an operating retail motor vehicle fueling station located in a commercial district near Interstate 5 in Stockton, California. The station has a small retail store located in the one-story building on site. It is located west of Interstate 5 on West Hammer Lane (Site Location Map, Figure 1). The Site is located in a commercial district used as a servicing point for travelers from the Interstate. The commercial district is surrounded by residential and agricultural properties (Site Plan with Well and Soil Boring Locations, Figure 2). In July 1990 a fuel vapor monitoring system detected petroleum hydrocarbon vapors in the subsurface, near the vicinity of the underground storage tanks (USTs). ExcelTech conducted a �. subsequent investigation to determine the source of the system alert. Soil excavation revealed that the fuel pipeline supplying the north pump island had leaked and an area of the piping trench backfill and surrounding soil had been impacted. ExcelTech excavated petroleum- hydrocarbon impacted soil and backfill material until field instrumentation and observation indicated its removal. Confirmatory soil samples were collected and submitted to a lab for analysis. The piping was repaired and the excavation was backfilled with clean material. Four monitor wells were also installed in 1990 to enable ongoing sampling and analysis of the groundwater underlying the Site. A single soil boring was also advanced during the investigation (identified as boring "B"). Subsequently an additional seven monitor wells have been installed on and around the Site. In 1991 monitor well MW-1 was abandoned by being over drilled and grouted due to concerns it may serve as a conduit between two shallow water bearing zones. It was replaced by monitor wells MW-1 R and MW-5, which are screened at two ` different depths to monitor the two water bearing zones. Monitor wells MW-9 and MW-10 were decommissioned in 2006 after being damaged during site construction activities. It was determined that these wells did not need to be replaced. A Site Conceptual Model (SCM)was prepared and submitted to the SJCEHD on November 28, 2006. The SCM documented the rate of plume migration, plume disposition overtime, environmental and human health screening levels and contaminant mass in soil and groundwater. SJCEHD reviewed the SCM and concurred with ATC's assessment that methyl tert butyl ether(MTBE) appears to be stable, shrinking and remains within the Site boundaries. ATC requested to reduce the frequency of monitoring events from quarterly to semiannually due to low level concentrations of chemicals of concern (COC) in groundwater samples collected from the monitor well network. In a letter sent to Quik Stop Market, Inc., dated May 7, 2008, the �. Quik Stop Market No. 132 July 21, 2011 ATC Project Number 75.62503.3206 Page 1 of 5