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r d o DOSERVICES, INCORPORATED MPDS-UN0788-09 December 12, 1996 3 Unocal Corporation 2000 Crow Canyon Place, Suite 400 P.O. Box 5155 San Ramon, California 94583 Attention: Mr. Edward C. Ralston RE: Semi-Annual Data Report Unocal Bulk Plant #0788 8203 East 11th Street Tracy, California Dear Mr. Ralston: 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 monitoring wells at the site were monitored three times and sampled once during this reporting period. 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 at the site is shown on the attached Figures 1 through 3. Ground water samples were collected on November 6, 1996. Prior to sampling, the wells were each purged of between 8.5 and 21 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 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 2. The concentrations of Total Petroleum Hydrocarbons (TPH) as gasoline, TPH as diesel, and benzene detected in the ground water samples • collected during this reporting period 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)889-1918