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Quik Stop Market No. 132 July 11, 1991 Project No. 3-49132-31 Page 1 PHASE III SOIL AND GROUNDWATER INVESTIGATION AT QUIK STOP MARKET NO. 132 3555 W. HAMMER LANE STOCKTON, CALIFORNIA INTRODUCTION At the request of Quik Stop Markets, Exceltech, Inc., has continued its field investigation to assess site contamination at the Quik Stop Market located at 3555 W. Hammer Lane, Stockton,California. The location of the site is shown in Figure 1. This report will present the background of the project, the scope of work, a description of the field investigation and sample analyses, a summary of findings, discussion, recommendations, and regulatory reporting requirements. ]BACKGROUND Quik Stop Market No. 132 formerly utilized three underground fuel-storage tanks on- site; two 10,000-gallon tanks contained regular unleaded and leaded gasoline and one 8,000-gallon tank contained super unleaded gasoline. In 1987, Exceltech installed a vadose monitoring system around the tanks at the site. This system detected hydrocarbon contamination in July 1990. Gasoline-contaminated backfill was removed from the trenches. Soil samples were collected and analyzed for gasoline components. The results of the analysis revealed that hydrocarbons penetrated the soil adjacent to the east half of the product line trench, which serves the north pump island. Exceltech drilled four exploratory borings and converted one boring to a groundwater monitoring well on August 23, 1990. The results of soil analysis of the soil samples from three borings showed little or no petroleum hydrocarbon contamination. One boring near the northwest portion of the north pump island contained 450 parts per million (ppm) total petroleum hydrocarbons as gasoline (TPHG). The groundwater from monitoring well MSV-1 contained 470 parts per billion (ppb? TPHG and 21 ppb benzene as well as detectable levels of toluene, ethyl benzene, and total xylenes. On September 11, 12 and 13, 1990, Exceltech drilled five exploratory borings and converted three of them to groundwater monitoring wells, monitoring groundwater located in a "lower" sandy unit. The results of soil analysis of the soil samples from _.