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3 <br /> Beacon Station No.474 August 2, 1996 <br /> Stockton,California Assessment Report <br /> Groundwater Samples <br /> Groundwater samples collected from groundwater monitoring wells MW-4 MW-5 were <br /> submitted to WEST under COC. Groundwater samples were analyzed for TPHg, BTEX, <br /> and MTBE by modified EPA methods 3550/8015/602. These laboratory results are <br /> summarized in Table 2. Gasoline hydrocarbons were detected in the water samples collected <br /> from the wells with reported concentrations of 1.6 parts per billion (ppb) benzene, 3.1 ppb <br /> toluene, 2.4 ppb total xylenes, and 5.7 ppb MTBE in the water sample collected from well <br /> MW-4, and 0.56 ppb toluene in the water sample collected from well MW-5. All other <br /> gasoline hydrocarbons analyzed for were not present above the laboratory reporting limits in <br /> the water samples. Laboratory analytical reports and COC forms for the groundwater <br /> samples are included in Appendix E. <br /> CONCLUSIONS <br /> Based on the data collected during this investigation Horizon concludes the following: <br /> • MTBE does not appear to be present in soil beneath the site or beneath the street area <br /> north of the site. <br /> • Gasoline hydrocarbons appear to be laterally and vertically delineated in the soil beneath <br /> the site and beneath the street area north of the site. <br /> • Gasoline hydrocarbons were detected in the groundwater at low concentrations in the <br /> area north of the site. <br /> • No additional work other than continued groundwater monitoring is warranted for this <br /> site at this time. <br /> 6 <br /> 1474.11-RPT HORIZON ENVIRONMENTAL INC. <br />