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Quik Stop Markets, Inc. September 6, 1991 <br /> Project No. 3-49132-31 Page 1 <br /> JULY 1991 QUARTERLY <br /> GROUNDWATER SAMPLING AND ANALYSIS <br /> FOR <br /> QUIK STOP MARKETS, INC. <br /> QUIK STOP NO. 132 <br /> 3555 W. HAMMER LANE <br /> STOCKTON, CALIFORNIA <br /> Introduction <br /> Exceltech, Inc., has completed the July 1991 sampling program to ascertain the <br /> groundwater conditions beneath Quik Stop Market No. 132, located at 3555 W. Hammer <br /> Lane in the City of Stockton,San Joaquin County,California(see Figures 1 and 2). <br /> The monitoring wells are sampled quarterly to monitor the shallow groundwater underlying <br /> the site. The program objectives are listed below: <br /> • Measure depth of gro:mdwater. <br /> • Plot groundwater contour surface within the site boundaries. <br /> • Sample and analyze groundwater samples. <br /> • Compare current and past data. <br /> The existence and degree of petroleum hydrocarbons in the groundwater underlying the site <br /> is determined by(1) the presence of free-floating product; and,(2)laboratory analyses of <br /> groundwater samples to determine concentrations of total petroleum hydrocarbons as <br /> gasoline(TPHG),as well as benzene,toluene,ethyl benzene,and total xylenes(BTEX). <br /> Background <br /> Quik Stop Market No. 132 formerly utilized three underground fuel-storage tanks on-site; <br /> two 10,000-gallon tanks contained regular unleaded and leaded gasoline and one 8,000- <br /> gallon taruk contained super unleaded gasoline. In 1987, Exceltech installed a vadose <br /> monitoring system around the tanks at the site. This system detected hydrocarbon <br /> contamination in July 1990. Gasoline-contaminated backfill was removed from the product <br /> samples of the native soil line trenches and l at the bottoms of the trenches were collected and <br /> analyzed for gasoline components. The results of the analysis revealed that hydrocarbons <br /> penetrated the soil adjacent to the east half of the product line trench which serves the north <br /> pump island. <br /> Exceltech drilled four exploratory borings and converted one boring to a groundwater <br /> monitoring well on August 23, 1990. The results of laboratory analyses of soil samples <br /> from three borings showed little or no petroleum hydrocarbon contamination. Soil samples <br /> from one boring near the northwest portion of the north pump island contained 460 parts <br /> per million(ppm)TPHG. The groundwater sample from monitoring well MW-1 contained <br />