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Wm.J,Hunter&Associates . PLATES II through VII are maps showing the approximate lines of equal concentrations of benzene, ethylbenzene, toluene, xylene, TPHg, and MTBE based upon this latest sampling event. They reveal that the placement of the 3 additional wells have defined the limits of BTEX & TPHg contamination. The results of that work is detailed in the WJH report titled "Interim Report Covering Results of Site Investigation.....; dated October 6, 2000. i A review of the data reveals that the highest levels of BTEX & TPHg continue to be centered around MW-1, which is the closest to the site of the removed UST. Those substances are not present in any other wells on the property. The presence of MTBE in MW-4, 5, & 6, increasing to the north, does not ft the pattern established for BTEX & TPHg. As shown on PLATE VII, concentrations of MTBE are highest in MW-6, which is the farthest well from the site of the removed UST. This suggests an offsite source for that compound that has not yet been identified. MTBE was measured only once in the well nearest the tank site, MW-1, in July, 2000, (TABLE I), and that analysis was not confirmed by the lab, and is considered unreliable. It has not been detected since. In order to evaluate the possibility of an offsite source of MTBE, we believe a receptor survey should be conducted to the northwest, north, and northeast of the site. We will have a workplan prepared and submit it to your department for approval. After receiving approval from the EHD, we will obtain authorization from the Cleanup Fund • staff and schedule the work. We will keep your office informed of progress. O-. tnter, RG Wr &Associates August 8, 2001 cc: Valley Wholesale Drug Co. CVRWQCB Geologic Technics. v rrrr`'Yn c^�tlI] FjW',-M I ff6'. ER * N0.860 or CALIF6��P 2