ARCHIVED REPORTS_PRELIMINARY ASSESSMENT_SITE INVESTIGATION REPORT

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4.0 FINDINGS Versar's findings are based on the results of our Site visits and interviews with Site personnel, review of CA ARNG files obtained from the Stockton facility and the CA ARNG headquarters in Sacramento, observations of the Site, field investigations, laboratory analyses of selected samples, and the results of a geophysical investigation. 4.1 Soil and Soil Vapor Investigation The results of the soil and soil vapor samples collected from the AASF, CSMS, and OMS areas of concern are presented in the following subsections. The mobile and fixed-base laboratory analytical reports are presented in Appendix D. 4.1.1 AASF Soil and soil vapor samples were collected from boring B-1 and B-3, and soil vapor samples were collected from borings B4 and B-5. The proposed boring B-2 was eliminated after discussions with Stockton CA ARNG personnel regarding the layout of the sewer lines and clarifier at the AASF. Sample intervals and analyses proposed for boring B-2 were combined with those proposed for B-1, as this boring was located near the clarifier to be investigated by boring B-2. The soil analysis results are summarized in Table 1, soil vapor analytical results are summarized in Table 2. The analytical findings for the AASF are summarized on Figure 5. The soil vapor sample results were below method detection limits for Methods 8260B and TO-14 for VOCs at all six boring locations. Petroleum hydrocarbons and elevated levels of metals were detected in soil in borings B-1 and B-3. TPH-g was detected in soil at 60 mg/kg at 2 feet bgs at boring B-3. TPH concentrations were below method detection limits at boring B-1. Borings B-1 and B-3 soil samples were analyzed for potential impacts from metals associated with waste oil and lead-acid batteries, respectively. Elevated concentrations of zinc were detected at boring B-1 at 10 feet and 15 feet bgs at 353 mg/kg and 365 mg/kg, respectively. Concentrations of the remaining metals tested for appear to reflect expectable background concentrations in the area (USGS, 1984). 4.1.2 CSMS Soil and soil vapor samples were collected from borings B-6 through B-8, B-10, and B-14 through B-19. Soil samples were collected in borings B-9, and B-11 through B-13. The soil and soil vapor analytical results are summarized in Tables 1 and 2,respectively. The locations of the borings are shown on Figure 4. A figure providing positive analytical results at each location is presented as Figure 6. The soil vapor sample results were below method detection limits for Methods 8260B and TO-14 for VOCs at all nine boring locations where soil vapor samples were collected. Petroleum • 2187-01/3134-100/MAY26'00 10