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June 29, 1988 AGS Job No. 86091-6 Page 2 Samples of ground water from the air-fluid interface were collected after initial water levels measurements in the monitoring wells. These samples were collected for subjective analyses by lowering a Teflon bailer approximately halfway through the interface. The bailer was then retrieved, and the water sample was examined for floating product, sheen, and Other subjective evidence of hydrocarbon contamination. No floating product, product sheen, emulsion, or odor was noted in samples from the monitoring wells. Results of these and previous subjective analyses are presented in Table I. Monitoring wells MW-1, MW-2, and MW-5 are 4-inch-diameter wells, and were purged prior to sampling with an electric submersible pump, sixty to 75 gallons of ground water were removed from each well. Well MW-4 is a 2-inch-diameter well, and 30 gallons of ground-water were purged from it with an a-ir-lift-' pump prior to sampling. After purging, samples were collected by lowering a clean Teflon bailer through the air-water interface. The water was then transferred to laboratory-cleaned, 40-milliliter glass volatile organic analysis vials. A Chain of Custody Record was initiated in the field by the sampler and accompanied the samples to Applied GeoSystems' analytical laboratory in Fremont, California. A copy of this record is attached. The samples were analyzed for total petroleum hydrocarbons (TPH) i by the Environmental Protection Agency (EPA) Method 8015 (modified for gasoline) , and for the volatile hydrocarbon constituents benzene, ethylbenzene, toluene, and total xylene isomers (BETX) by EPA Method 602. Applied GeoSysteMts' laboratory is certified by the state of California for these analyses. Copies of the laboratory Records of Analyses are attached. The results of tihe laboratory analyses, summarized in Table 2, indicate that the concentration of benzene in ground water taken from monitoring wells MW-1, MW-2, and MW-4 exceeds the maximum level for drinking water recommended by the California Department of Health Services (DHS) . The concentration of the other volatile constituents in these wells are below the maximum levels for drinking water recommended by the DHS. The concentration of all volatile constituents in ground water from well M4-5 aretvery low (below detection limits except for toluene) , suggesting contamination of ground water by dissolved volatile constituents (BETX) is restricted to the vicinity of the tank cavity. With the exception of the benzene cor -:entration in well MW--4 , the concentrations of all hydrocarbon constituents in groundwater from all wells has decreased since the last sampling I®Iv