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11 ' event. MW-1 continues to have the highest concentration of the monitoring wells with gasoline contamination of TPHg at 149,000 ppb, which is higher by 5,000 ppb over the last sampling event. EW-1 had a concentration of TPHg of 216,000. The groundwater hydraulic gradient was calculated . at S=0.004 with the down slope in the easterly direction, which is a change from the northeast direction of the normal site gradient. The gradient is determined by the first ground water elevation data of MW-1, MW-2, and MW-3 (see a site map attached). Analysis for oxygenates during this event indicates the presence of both MTBE and/or 1,2 DCA in moderate amounts in MW-1, MW-2, MW-5, MW-8S and EW-1. EW-1 had the highest concentration of both MTBE at 1500 ppb, andl,2 DCA at 360 ppb, and EDB at 420 ppb. (see attached recap sheets). Monitoring well MW-8S appears to have recovered from the damage done by the demolition of the building on the property directly east of its location. TPHg has fallen from 5730 ppb on March 23, 2003,to non-detect during this event. This is most likely a result of the purging of the well during the last four sampling events. The extraction well EW-1 produced the highest concentrations of TPHg,MTBE, 1,2 DCA and EDB with TPHg at 216000 ppb compared to 227,000 ppb from the last sampling event. Conclusions The results are mixed as to trends in concentrations of the spill. Last quarter results tend to enforce the theory that natural attenuation was lowering the concentration in all the monitoring points. The results of this event were mixed, with some points higher and some points lower. EW-1, that is • located in the southeast corner of the UST excavation, has produced the consistent results with a variance of less than 10% over four sample events. Recommendations The author recommends that monitoring well sampling be continued on a quarterly basis with analysis for TPHg, BTEX, and oxygenates. Work in Progress The present work plan calls for mobilization of a discharge tank and pump installation for the proposed pump test. This work will be started when the State UST Fund is current on reimbursement for this site. At the present time, funds for the completion of this work plan are not available. Please contact Ervin Rifenburg of this office at (209)368-9381 if you have any questions on this report. Q�rEsslo' Respectfully submitt ►FAF ;Foothil nBering Ervin Rife b g, P OF Attachment . Groundw ter Analysis Recap, i aps,Del-Tech Monitoring Report,Lab Reports cc: Michael D. & Sharon Qlivarez, 436 W. Scotts Ave. Stockton, Ca. i 3