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EW-1 had a concentration of TPHg of 222,000, which is 6,000 ppb higher from last quarter. The <br /> groundwater hydraulic gradient was calculated at S=0.004 with the down slope in the North/Easterly <br /> direction,which is the normal site gradient for winter/spring.The gradient is determined by the first <br /> ground water elevation data of MW-1, MW-2, and MW-3 (see a site map attached). <br /> Analysis for oxygenates during this event indicates the presence of both MTBE and/or 1,2 DCA in <br /> moderate amounts in MW-2, MW-3, MW-5, MW-7, MW-8S and EW-1. EW-1 had the highest <br /> concentration of both MTBE at 1200 ppb, andl,2 DCA at 550 ppb, and EDB at 490 ppb. (see <br /> attached recap sheets). <br /> The extraction well EW-1 produced the highest concentrations of TPHg,MTBE, 1,2 DCA and EDB <br /> with TPHg at 222,000 ppb compared to 216,000 ppb from the last sampling event. <br /> Conclusions <br /> The results are mixed as to trends in concentrations of the spill. Last quarter results tend to enforce <br /> the theory that natural attenuation was lowering the concentration in all the monitoring points. The <br /> results of this event were mixed, with some points higher and some points lower. EW-1, that is <br /> located in the southeast corner of the UST excavation, has produced near equal results from March <br /> of 2003. This indicates to the author that natural attenuation is playing a minor roll in remediation. <br /> The changes in concentration over the last year appear to be the result of the eye of the plume simply <br /> moving around with the movements of the groundwater. <br /> Recommendations <br /> The author recommends that monitoring well sampling be continued on a quarterly basis with <br /> ianalysis for TPHg, BTEX, and oxygenates. <br /> Work in Progress <br /> The present work plan calls for mobilization of a discharge tank and pump installation for the <br /> proposed pump test.This work will be started when the State UST Fund is current on reimbursement <br /> for this site. At the present time, funds for the completion of this work plan are not available. <br /> Please contact Ervin Rifenburg of this office at (209)368-9381 if you have any questions on this <br /> report. <br /> Respectfully submitted, pe4,Q, bERrL '��Z <br /> Foothill Enginee ' g s O p5774T 4'n <br /> 2�v g d <br /> ST <br /> Mike Vlach, PE <br /> Attachments: Groundwater , Site Maps,Del-Tech Monitoring Report,Lab Reports <br /> cc: Michael D. & Sharon 4livarez, 436 W. Scotts Ave. Stockton, Ca. <br /> 3 <br />