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z z z 2 - N O E)OSERVICES,N INCORPORATED � a ❑ MPDS-UN0123-11 December 26, 1997 Unocal - DBG/AMG 2121 N California Blvd , Suite 250 Walnut Creek, California 94596 Attention Mr Robert A Boust RE Quarterly Data Report Former Unocal Service Station # 0123 1034 Central Avenue Tracy, California Dear Mr Boust This data report presents the results of the most recent quarter of monitoring and sampling of the monitoring wells at the referenced site by MPDS Services, Inc RECENT FIELD ACTIVITIES The monitoring wells that were monitored and sampled during this quarter are indicated in Table 1 Prior to sampling, the wells were checked for depth to water and the presence of free product or sheen The monitoring data and the ground water elevations are summarized in Table 1 The ground water flow direction during the most recent quarter is shown on the attached Figure 1 Ground water samples were collected on December 2, 1997 Prior to sampling, the wells were each purged of between 4 and 6 gallons of water During purging operations, the field parameters pH, temperature, and electrical conductivity were recorded on the purging/sampling 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 state-certified laboratory MPDS 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 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 to date are summarized in Tables 2, 3, and 4 The concentrations of Total Petroleum Hydrocarbons (TPH) as gasoline, TPH as diesel, and benzene detected in the ground water samples collected this quarter are shown on the attached Figure 2 Copies of the laboratory analytical results and the Chain of Custody documentation are attached to this report 2401 Stanwell Drive Suite 400 Concord CA 94520 TEL (510)602 5120 FAX (510)689 1918