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M. Scott Mansholt - 2 - 17 February 2006 <br /> Chevron <br /> Former TAOC Tracy Pump Station <br /> In addition, consistent with previous results, petroleum hydrocarbon constituents were not detected in <br /> upgradient well REW-1. Total petroleum hydrocarbons as gasoline (TPH-g), benzene, toluene, <br /> ethylbenzene, and xylenes (BTEX), and polynuclear aromatic hydrocarbons (PAHs)were not detected in <br /> the two downgradient wells. This quarter, TPH as diesel (TPH-d)was detected in the downgradient <br /> wells at concentrations of 510 µg/L (Well E) and 220 µg/l, (Well F). These results have showed little <br /> variation and are consistent with TPH analytical data collected since 1996. <br /> Based on the quarterly monitoring findings by Geomatrix and our review of the report, we have the <br /> following comments: <br /> • During recent conversation with Central Valley Water Board staff, Geomatrix indicated that, <br /> since groundwater conditions at the site are relatively unchanged since 1996, Geomatrix <br /> recommended that quarterly sampling and monitoring be discontinued. Central Valley Water <br /> Board staff concurs that groundwater conditions are stable, however, the sampling and <br /> monitoring can be reduced to an annual frequency. <br /> • Product removal should continue quarterly commencing with the first quarter of 2006. <br /> If you have any questions,please call Dean Hubbard at (559) 445-5179. <br /> 6 <br /> SHELTON R. GRAY C. DEAN HUBBARD <br /> Senior Engineering Geologist Professional Geologist <br /> PG No. 6357 <br /> cc: Michael Infurna, Jr., San Joaquin County EHD, Stockton <br /> Gary Foote, Geomatrix, Oakland <br /> Luis Mercado, SAIC, Sacramento <br />