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Quarterly Ground-Water Monitoring October 4, 1989 Beacon Station No. 22-1, Lockeford, California AGS 87048-2 i I I slopes slightly to the west. We understand from Sharbob personnel that the dry wells were destroyed within a month after the sampling. Ground-water monitoring was also conducted in October 1987, April 1988, and July 1988 (Applied GeoSystems Report 87048-2, November 17, 1987, June 7, 1988, and October 25, 1988). These later monitoring events have indicated lower levels of ground-water contamination in all four wells. The highest level of hydrocarbon contamination is still in i well MW-2 which further suggests drainage into the former dry wells may have been the I source of hydrocarbon contamination. At the request of Sharbob, a geologist from our office was at the site on August 2, 1989, to collect ground-water samples from the four wells. The depth to the ground-water surface was measured and the water was subjectively analyzed in each monitoring well using methods outlined in the Field Procedures attached to this letter report. The total depth of each well was also measured. Cumulative results of subjective analyses are summarized in Table 1. No floating product or product sheen was noted in the wells. Ground water was found to be approximately 3 feet deeper than previously measured. Ground water from each monitoring well was purged and sampled by methods outlined in the Field Procedures attached to this letter report. The field geologist initiated a Chain of I Custody Record and it accompanied the samples to the analytical laboratory. A copy of that record is attached to this letter report. I The groundwater samples were analyzed for total petroleum hydrocarbons (TPH) using E Environmental Protection Agency (EPA) Method 8015 and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using EPA Method 602 at the Applied GeoSystems laboratory in Fremont, California, (Hazardous Waste Testing Laboratory Certificate No. 153). Cumulative results of laboratory analyses are summarized in Table 2. Copies of the laboratory Analysis Reports are attached to this letter report. Laboratory results of water samples from well MW-2 indicate the TPH concentration increased from 0.52 ppm to 1.1 ppm since the last sampling in July 1988. The benzene concentration increased from 0.0354 ppm to 0.039 ppm. The drinking water standard set by the California Department of Health Services (DHS) for benzene is 0.001 ppm. Toluene and total xylene isomers increased approximately 0.001 ppm. The ethylbenzene concentration decreased from 0.0034 ppm to 0.0015 ppm. Laboratory results of water samples from wells MW-1, MW-3, and MW-4 indicate TPH and BTEX levels are below the detection levels for the tests used except for the TPH level in well MW-1 which was 0.025 ppm- The ground-water gradient was evaluated to provide an indication of the direction of I ground-water flow at the site. Differences in height among the tops of the well casings were I 2 II i k AV,0A6d GeoSystems -- - - - -- - -- - - --