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P INTERIM PROBLEM ASSESSMENT REPORTMgTERM REMEDIAL ACTION PLAN -6- Former Beacon Station No. 494, 2185 East Fremont Street Stockton, CA—AMV Project No. 19005.07 3• .1 Tank Basin Sam li n AMV collected six soil samples from the tank basin for laboratory analysis (Figure 3). Each sampling location was about 2 feet beneath the end of an underground storage tank. Collected ' soil samples were analyzed for TPHg, total lead by EPA Method 7420, and ethylene dibromide (EDB) by EPA Method 8240. Table 4 summarizes the analytical results for soil samples collected from the underground storage tank basin. Five of the six soil samples were nondetectable for TPHg, and in the sample with detected TPHg, the concentration was less than 1 mg/kg. Benzene and EDB were ' nondetectable in all samples. The highest total lead result was 7.5 mg/kg. Appendix H contains copies of the certified analytical reports. 3 3.2 Pi in Trench Sam lin In addition to the tank basin samples, AMV collected four soil samples from the bottom of the piping trenches at the locations shown on Figure 3. Sampling locations were discussed with Ms. Carol Oz of San Joaquin County. Each sample was collected from a depth of about 4.5 feet below grade. These samples were analyzed for BTEX, TPHg, total lead, and EDB. Table 5 summarizes the analytical results for the soil samples from thei in p p g trenches. All samples were nondetectable for TPHg, benzene, and EDB. The highest result for total lead was ' 8.2 mg/kg. Appendix I contains copies of the certified analytical reports. 3.4 Limited Soil Gas Screening On March 17 and 18, 1993, the firm Remediation Testing and Design (RTD) conducted a limited soil gas screening at the site. In addition to using four of the five existing monitoring ' wells, and the eight existing vapor extraction wells, RTD installed nine 3/4-inch vapor probes for the soil gas screening. Probe installation depths ranged from 11 to 17 feet below surface grade. Figure 4 shows the locations of the installed vapor probes P-1 through P-9. ' 3.4.1 Test Procedure The test procedure consisted of purging two to five casing/probe volumes of soil vapor from the probe or well being tested, followed by field screening of the extracted soil vapor for the presence of volatile hydrocarbons using a flame ionization detector (FID). After the FID ' reading, RTD collected (from selected wells) a soil vapor sample in a 1-liter Tedlar bag for laboratory analysis. Air samples were submitted for analysis of BTEX and TPHg. r toos.mi