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0. N SERVICES, INCORPORATED a M n 7 . MPDS-UN2859-11 June 5, 1996 Unocal Corporation 2000 Crow Canyon PIace, Suite 400 P O Box 5155 San Ramon, California 94583 Attention Mr Robert A Boust RE Quarterly Data Report Former Unocal Service Station #2859 1665 Pacific Avenue Stockton, 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 May 8, 1996 Prior to sampling, the wells were each purged of between 10 and 17 5 gallons of water During purging operations, the field parameters pH, tempera- ture, and electrical conductivity were recorded and are presented in Table 2 Once the field parameters were observed to stabilize, and where possible, a minimum of approximately four 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 Field blank, Equipment blank and Trip blank samples (denoted as ES 1, ES2 and ES3 respectively) were also collected for quality assurance and control MPDS Services, Inc transported the purged ground water to the Unocal 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 Table 3 The concentrations of Total Petroleum Hydrocarbons (TPH) as gasoline 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