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S� California Fuels D August 15, 1989 (89062) At each soil vapor monitoring point, a 7/8-inch outside diameter, hollow steel probe was driven 3 to 6 feet below ground surface (bgs) with a jack- hammer. Dense, hard soil conditions were encountered at depths between 3 and 6 feet bgs, therefore, we were unable to analyze vapors greater than 6 feet in depth. The hollow probe was connected to a peristaltic pump and a photoioniza- tion detector (PID) using teflon tubing and stainless steel appurtenances. Soil vapors were purged from the sampling location for 2 to 3 minutes before the soil vapor sample was routed to the PID for detection and measurement via the three- way valve. A vacuum gauge was connected in series with the sampling system to check the sampling location for blockage (i.e. , a vacuum is created if the slots in the probe become plugged) . The PID is a direct reading instrument (digital read-out) equipped ' with an internal sampling pump with a flow rate of 275 milliliters per minute (ml/min) . Once the PID reading stabilized, the valve was recorded. Before recording the volatile hydrocarbon concentration, the location was purged and sampled at least three times in sequence to check for variability in the data. FINDINGS ■ SITE CONDITIONS The Pacific Pride Cardlock facility is located in the City of Stockton, California. The site is bordered by commercial property (office buildings) to the north, west and south. Residential apartments border the site to the east. The site is located on filled marshland of the San Joaquin Valley. The area is drained by the Calaveras River located approximately 1 mile to the 1 north and the San Joaquin River approximately 3 miles to the southeast. The San Joaquin Environmental Health Department (EHD) estimates ground water to be present at 50 to 60 feet beneath the site. SOIL VAPOR i The results of the soil vapor survey are presented in Table 1 - Results of Soil Vapor Survey. The survey indicates elevated levels of hydrocarbon vapors near the fill ports of the regular and unleaded gasoline tanks. Elevated levels of hydrocarbon vapors were also detected north of the dispenser island. These elevated hydrocarbon vapor levels may be related to a deteriorated product line that was replaced sometime in the past. Organic vapors from this source do not seem to have migrated a significant distance, with hydrocarbon vapor concentrations having dropped off to essentially background levels approximately 10 to 15 feet from the apparent source.