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Quarterly Mnnitaritrg Report January 13, 1989 Former U11OCAL Station No. 2859, Stockton, California AGS 38012-2 calculations of ground--water elevations indicate that the direction of ground-water flow at the site Is north 51 degre-en east. The calculated direction of ground-water flow on June 6, 1988, was north 34 degrees east. The average gradient at the time of mea:;urement was 0.68-foot in vertical distance per 100 feet horizontal distance (36 feet per mile) . These values are greater than those calculated during the previous sampling event of June 6, 19n8. During that investigation, the average gradient was 0.17-foot vertically per 100 feet horizontally. Ground-water samples were collected from near the air-fluid interface in the monitoring wells for subjective analyses b lowerirg approximately half the length of a clean Teflon bai'er past 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, or emulsion was noted in samples from the InGilitoring wells. The results of these subjective analyses are presented in Table 1. Approximate'y three well volumes (30 gallons) of ground water o. were purged from the wells using a submersible pump. Recharge to the wells was relatively rapid. Ground-water samples for laboratory analysis were then collected from the monitoring wells by lowering a clean Teflon hailer past the air-water interface to a point immediately below the top of the water.- column. The bailer was then recovered and the sample slowly transferred to + laboratory-cleaned, 40-milliliter glass vials. Concentrated hydrochloric acid was added to each sample as a preservative. The sample containers were then labeled and immediately placed in iced storage. Chain of Custody Records were initiated by the geologist and accompanied the samples to the analytical labora- tories. A copy of this record is attached to this letter report. The ground-wa-er samples were analyzed for total petroleum hydrocarbons (TPH) as gasoline using Environmental Protection Agency (EPA) Method 8015 and the volatile hydrocarbon constituents benzene, ethylbenzere, toluene, and total xylene isomers (BETX) by EPA Method 602 at Applied GeoSystems' laboratory in Fremont, California. The results of these and previous analyses are summarized in Table 2. The results of the analyses indicate that 1) levels of TPH as gasoline and BTEX remain ncndetectabl, in.._well..MW-11..-...2).-_concen-. _...... tra ions of TPH as gasoline, benzene and toluene have F. substantially increased in well MW--2, and 3) hydrocarbon __ •4Pp/149t' 0e0Systems —