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rr 7 7 Y Lori Duncan EH From: Eric Price [eprice@Geologicaltechnics.com] Sent: Thursday, April 19, 2007 6:17 AM To: Lori Duncan [EH] Subject: RE: Sinclair Trucking, 3780 Linne Rd W., Tracy Hi Lori, Here is a narrative of the attenuation analysis. As soon as Virginia gets into the office I'll have her send you the summary of analytical data and the two trend charts discussed below. I would do it myself but I don't know how to convert the charts to .pdf format. We concluded another round of monitoring on April 4, 2007, report should be out by next week. The results show all monitoring and domestic wells, except MW-1R, are non-detect above reporting limits for all analyzed constituents. MW-1R shows 0.13 mg/L TPH-g, 1.4 ug/L ethylbenzene, and 1.4 ug/L xylenes. The well was non-detect above reporting limits for all other analyzed constituents. A trend analysis of MW--1 shows a natural reduction of -58% per year in benzene levels. The well was abandoned in 2005, but projection of benzene reduction suggests that concentrations would fall below MCLS prior to April of 2008- A trend analysis of MW-1 shows a reduction of 18% between April 2005 and April 2006, and a 81% reduction between April 2006 and April 2007. The benzene levels have been below MCLS 6 of the last 9 quarters (non-detect for three of those events) . The trend shows that benzene levels may peak to approximately 7 ug/L this July. However, the projection of benzene reduction in MW-1R matches the predictions seen in MW-1 suggesting that benzene concentrations will fall below MCLs by April of 2008 and not rebound above MCLs again. The only other impacted well, MW-4, has been below MCLs for 15 of the last 16 quarters. In 25 quarterly monitoring events benzene levels surpassed MCLs five times. This well, directly downgradient from MW-1 and MW-1R, has been a sentinel to monitor attenuation. The elevated benzene concentrations seen in MW-1 in the past have never reached MW-4. This suggests that the contamination attenuates rapidly and supports the conclusions drawn above. Thanks, Eric Price Project Geologist -----Original Message----- From: Lori Duncan [EH] €mailto:lduncan@sjcehd.com] Sent: Friday, April 13, 2007 2 :41 PM To: Eric Price Subject: FW: Sinclair Trucking, 3780 Linne Rd W. , Tracy -----Original Message----- From: Jim Barton [mailto:jbarton@waterboards.ca.gov] Sent: Friday, April 13, 2007 9:45 AM To: Lori Duncan [EH] 1