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WFSTERN GEoI. nGIc, R1:501• }tCES , INC . I Randal!/15 Sepicmbcr 1989 1 ANAL171C RESULTS s - All groundwater samples,collected 12 June 1989,were analyzed by CCAS for TPPH by EPA Method 8260(formerly EPA Method 524.2/8240): The analytic results arc presented in Table 1. The analytic reports and quality, assurance/quality control reports are included as Appendix C,respectively. TPPH and benzcne distribution maps are shown in Figures 3 and 4. Both figures show the highest concentrations of hydrocarbon in the vicinity of well MW-1, at the south end of the site, decreasing to the north-northwest. TPPH,reported as gasolinr",were detected in groundwater samples from wells MW-I,h1W-2 and MW-5 at 30,000 ppb,11,000 ppb and 90o ppb,respectively. TPPH were not detected in the samples 1 from the other two wells. The highest concentration of benzene was detected at 4,400 ppb in samples from well MW-I �= at the south side of the site. Wel!MW-1 also contained 1,600 ppb toluene,5,900 ppb total xylenes,and 2,900 ppb ethylbenzene. BTEX were detected in samples from wells hfW-2 and hiW-5,where benzene concentrations were 1,210 ppb and 24 ppb,respectively. In addition,1,2-DCB was detected at 5.3 ppb in well MW-4. GROUNDWATER FLOW All monitoring wells on the site were surveyed for top-of-casing elevations by John Koch, a licensed land surveyor(#LS4811)on 28 March 1989 to the City of Stockton benchmark #218. Figure 5 shows the potentiometric surface of the shallow-water-bearing zone,based on depth" cl to-water measurements taken on 12 June 1989(Table 2). The approximate direction of groundwater ® flow is the to the east at a gradient of about 117c. TRENDS The analytic results for groundwater samples collected on 12 June 1989 show generally similar hydrocarbon concentrations to those previously reported for the initial sampling on 22 March 1959. TPPH concentrations remained the same in samples collected from wells MW-1 and MW-2 and declined _ in the sample collected from well MW-S from 4,000 ppm to 900 ppm when compared to samples collected during the prior sampling. The BTEX concentrations have increased somewhat in samples from wells MW-1 and MW-2. For example,the benzene concentrations rose from 3,600 ppb to 4,400 ppb and from 750 ppb to 1200 ppb,respectively. Groundwater samples from wells MW-3 and MW-4 4 i[lili:5l:9