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r i U.A "OYU, 47K-91704:1 I,! Tow A Fes'+ Quarterly Ground-Water Monitoring March 8, 1989 Beacon Station No. 3-492, Manteca, California AGS 86102-3 were also collected, but were not analyzed. A Chain of Custody Record was initiated by the field geologist and accompanied the samples to the analytical laboratory. A copy of that record is attached to this letter report. On the dates free product was present in well MW-1, it was removed by bailing. The free product and purge water was temporarily stored onsite in 55-gallon, labeled 17-E drums approved by the Department of Transportation pending removal by Beacon to their refinery in Hanford, California, and subsequent treatment in a waste water separator. The samples collected from monitoring wells MW-2 and MW-3 were analyzed at Applied GeoSystems' laboratory in Fremont, California (California Hazardous Waste Testing Laboratory Certificate No. 153) , for total petroleum hydrocarbons (TPH) as gasoline by '.� modified Environmental Protection Agency (EPA) Method 8015 and the purgeable gasoline constituents benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) by EPA Method 8020. The results of these and previous results are summarized in Table 2, and indicate that the benzene concentration in the r. sample from well MW-2 was above the action levels for drinking ?r water recommended by the California Department of Health Services (DHS) . The concentrations of toluene, ethylbenzene, and total xylene isomers in the sample from well MW-2 were below the detection limits or below the recommended action levels. TPH and BTEX concentrations in the sample from well MW-3 were below the detection limits of the methods used. Copies of the laboratory Analysis. Reports are attached to this letter report. The ground-water gradient across the site was evaluated by combining measurements of the static water level with the relative elevation of the top of the casing in each monitoring well. The relative elevation of the top of the casing in each well was previously evaluated with a Lietz/Sokkisha Che Automatic r Level. The static water levels ::ere adjusted using the top of the casing in well MW-2 as a common datum. These data are summarized in Table 3, and were used to evaluate the gradient of the stat'_c ground-water surface. On the dates the measurements were taken the maximum difference in the depth to the ground-- _;.� water surface in the three wells was evaluated to be less than 0.03 foot, which is within the instrument error over a distance of 75 feet. The ground-water gradient is, therefore, considered flat; similar results have been obtained during previous .._.______gradient.._evaluatigns___The ground-water gradient evaluations diva -.. the-pr _...... _... product in not include corrections for �esence of floating well MW-1. 3 ,4jOp/1490 GOOSStOMS