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Former Beacon Station 494 July 23, 1995 <br /> Stockton,Cahforma QuarterlyGroundwater Morutonn <br /> California Department of Health Services-certified analytical laboratory (ELAN No 1346) <br /> located in Davis, California Groundwater samples were analyzed for Total Petroleum <br /> Hydrocarbons as gasoline (TPHg) according to EPA Method 8015 and for benzene, toluene, <br /> ethylbenzene, and xylenes (BTEX) according to EPA Method 602 Laboratory results are <br /> summarized on Table 1 Copies of the laboratory reports and chain-of-custody are included in <br /> Attachment C Laboratory results tables from sampling prior to April 1995 are shown in <br /> Attachment D <br /> Results <br /> Water-level data were used to construct a Groundwater Contour Map (Figure 2) The <br /> groundwater elevation data reveal a circular depression in the groundwater surface centered <br /> toward MW-3 This data implies that the groundwater flow is radial at a gradient of <br /> approximately 0 14 toward the pumping well MW-3 Data collected before the start-up of the <br /> treatment system had shown a groundwater flow generally toward the northeast The change <br /> in gradient provides a strong indication that groundwater beneath the site is being affected by the <br /> groundwater extraction from MW-3 Groundwater in the wells has risen from 2 to 2 5 feet in <br /> the monitoring wells since the previous monitoring event This reflects the above-normal <br /> precipitation during early 1995 <br /> A Benzene Isoconcentration Map (Figure 3) is attached to this report Dissolved benzene <br /> concentrations were detected only in samples collected from monitoring wells MW-2 and MW-3 <br /> which contained 0 94 and 1 3 parts per billion, respectively Concentrations of benzene <br /> decreased in the last four sampling quarters in MW-2 and increased this quarter in MW-3 <br /> Report No 494gmr95 q2 <br /> Job No 1494 31 2 HORIZON ENVIRONMENTAL INC <br />