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r <br /> 3 z ? z <br /> [PLL)oSERVICES, INCORPORATED <br /> 0 0 0 0 <br /> • MPDS-UN5421-05 <br /> January 3 , 1996 <br /> Unocal Corporation <br /> 2000 Crow Canyon Place, Suite 400 <br /> P O. Sox 5155 <br /> San Ramon, California 94583 <br /> Attention Mr. Edward C. Ralston <br /> RE: Semi-Annual Data Report <br /> Unocal Service Station #5421 <br /> 7303 Pacific Avenue <br /> Stockton, California <br /> Dear Mr. Ralston <br /> This data report presents the results of the most recent semi-annual <br /> monitoring and sampling of the monitoring wells at the referenced site <br /> by MPDS Services, Inc <br /> RECENT FIELD ACTIVITIES <br />�) The monitoring wells that were monitored and sampled during this semi- <br /> annual period are indicated 3_n Table 1 . Prior to sampling, the wells <br /> were checked for depth to water and the presence of free product or <br /> sheen. The monitoring data and the ground water elevations are <br /> summarized in Table 1 The ground water flow directions during the <br /> most recent semi-annual period are shown on the attached Figures 1 and <br /> 2 . <br /> Ground water samples were collected on December 1, 1995 . Prior to <br /> sampling, the wells were each purged of between 11 5 and 16 5 gallons <br /> of water. During purging operations, the field parameters pH, tempera- <br /> ture, and electrical conductivity were recorded and are presented in <br /> Table 2 Once the field parameters were observed to stabilize, and <br /> where possible, a minimum of approximately four casing volumes had been <br /> removed from each well , samples were then collected using a clean <br /> Teflon bailer. The samples were decanted into clean VOA vials and/or <br /> one-liter amber bottles, as appropriate, which were then sealed with <br /> Teflon-lined screw caps, labeled, and stored in a cooler, on ice, until <br /> delivery to a state-certified laboratory Field blank, Equipment blank <br /> and Trip blank samples (denoted as ES1, ES2 and ES3 respectively) were <br /> also collected for quality assurance and control MPDS Services, Inc . <br /> transported the purged ground water to the Unocal Refinery located in <br /> Rodeo, California, for treatment and discharge to San Pablo Bay under <br /> NPDES permit <br /> ANALYTICAL RESULTS <br /> The ground water samples were analyzed at Sequoia Analytical Laboratory <br /> and were accompanied by properly executed Chain of Custody documenta- <br /> 2401 Stanwell Drive Suite 300 Concord CA 94520 <br /> TEL (510)602-5120 FAX (510)689-1918 <br />