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FIRST QUARTER REPORT K"WIKEE FOODS 2081 Country Club Boulevard Stockton, California .June I5, I998 EXECUTPVE SUMMARY Two I0,000-gallon unleaded gasoline storage tanks were removed from the Kwikee Foods property at 2081 Country Club Boulevard in Stockton, California in the first quarter of 1998. Each tank had two holes, indicating that the USTs are a probable source of the gasoline that had been detected in previous monitoring of the groundwater at the site. Upgradient Environmental Consultants therefore submitted an addendum to its earlier work plan for site assessment. The addendum proposed drilling five Geoprobe borings around the UST cavity to investigate the lateral and vertical extent of soil contamination. It was approved on May 5, 1998 by San Joaquin County PHS/EHD and the work was performed on May 11. Groundwater monitoring was performed the following day, and 14 soil samples and 3 water samples were transported to Sequoia Analytical for analysis of gasoline, BTEX, and 7 gasoline oxygenates. Three samples were also delivered for • analysis of Total Organic Carbon. In addition, 3 soil samples were sent to Cytoculture, Inc. for analysis of hydrocarbon-degrading bacteria, and 5 samples were sent to Sierra Testing Laboratories for measurement of hydraulic conductivity and porosity. The borings ranged in depth from 25 to 37 feet, for a total of 161 feet. Two borings were continuously sampled from 21 to 26 feet, as directed by PHS/EHD. Otherwise, samples were collected at 5-foot intervals. The borings were backfilled with cement grout after sampling. All probes penetrated three principal zones. The upper zone consists of silty clay or clayey silt, extending to a depth of 20 feet. This zone has a low hydraulic conductivity and forms an aquitard that confines water to the underlying sand zone. The sand zone is approximately 5 feet thick, is fine to coarse grained, and has moderate to high hydraulic conductivity. It overlies the lowest zone, which is a low-conductivity clay layer. Gasoline hydrocarbons were detected in three of the five probes, but at uniformly low concentrations. Benzene was the most frequently reported hydrocarbon (seven samples), but the highest concentration in any sample was only 0.058 mg/kg. Only one sample contained gasoline above the detection limit. Methanol was detected in four samples, TBA was detected in two samples, and MTBE was detected in one sample. The soil contaminant plume measures approximately 30 ft x 50 ft x 10 ft, for a total volume of 555 cubic yards. The average TPH and benzene concentrations within the plume are estimated to be 100 and 0.1 mg/kg, respectively. 1 I