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1 2 Z = Z 65 ¢ a a DOSERVICES, INCORPORATED a o a r . MPDS-UN5098-14 October 17, 1997 Unocal DBG/AMG 2121 N California Walnut Creek, California ovSuite 250 94596 Jam' �• Attention Mr Robert A Boust RE Annual Data Report Former Unocal Service Station #5098 5606 Pacific Avenue Stockton. California Dear Mr Boust This data report presents the results of the most recent monitoring and sampling of the monitoring wells at the referenced site by MPDS Services, Inc RECENT FIELD ACTIVITIES The Unocal monitoring wells that were monitored and sampled are indicated in Table I Prior to sampling, the Unocal wells were checked for depth to water and the presence of free product or sheen The monitoring data and the ground water elevations for the Unocal wells are summarized in Table 1 A point monitoring event was conducted with the consultant for the nearby Montgomery Ward site on September 16, 1997 The monitoring data collected for Montgomery Ward's monitoring wells (provided by Environmental Audit, Inc ) are summarized in Table 3 The ground water flow direction in the vicinity of the Unocal and Montgomery Ward sites during this most recent annual monitoring and sampling event is shown on the attached Figure 1 Ground water samples were collected from the Unocal wells on September 16, 1997 Prior to sampling, the Unocal wells were each purged of between 10 and 15 gallons of water During purging operations, the field parameters pH, temperature, and electrical conductivity were recorded on the purginglsampling data sheets which are attached to this report Once the field parameters were observed to stabilize, and where possible, a minimum of approximately three casing volumes had been removed from each well, samples were then collected using a clean Teflon bailer The samples were decanted into clean VOA vials and/or one-liter amber bottles, as appropriate, which were then sealed with Teflon-lined screw caps, labeled, and stored in a cooler, on ice until delivery to a ;tate-Certified iahoratnry KAPnS Services, Inc transported the purged ground water to the Tosco Refinery located in Rodeo, California, for treatment and discharge to San Pablo Bay under NPDES permit ANALYTICAL RESULTS The ground water samples collected from the Unocal wells were analyzed at Sequoia Analytical Laboratory and were accompanied by properly executed Chain of Custody documentation The analytical results of the ground water samples collected from the Unocal wells to date are summarized in Table 2 The concentrations of Total Petroleum Hydrocarbons (TPH) as gasoline and benzene detected in the ground water samples collected from the Unocal wells during this annual monitoring and 2401 Stanwell Drive Suite 3C0 Concord CA 94520 TEL (5 10)602-5120 FAX (510)689-1918