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r <br /> ARCADIS Ms. Lori Duncan <br /> October 8, 2008 <br /> - Frequency <br /> of Range of California Concentration of <br /> Detection Detected Primary Exceedances <br /> Above Concentrations MCLS in Frequency of in pg/L2 <br /> j- Constituent the MDL' in pg/L2 pg/L2 Exceedances (Well ID) <br /> 1ki TPH-DRO 5/5 280-520 -- -- -- <br /> TPH-GRO 1/5 820 -- -- -- <br /> Toluene 1/5 2 150 -- -- <br /> Ethylbenzene 1/5 21 300 -- <br /> Total Xylenes 1/5 53 1,750 -- <br /> MTBE 1/5 7 13 -- <br /> TBA 1/5 13 -- -- - <br /> 1,2-DCA 1/5 840 0.5 1/5 840(MW-1) <br /> Notes: <br /> 1. MDL=method detection limit. <br /> 2. pg/L=microgram per liter,equivalent to part per billion(ppb). <br /> 3. MCL=maximum contaminant level. <br /> The site assessment activities completed June 16 through June 23, 2008 have <br /> P 9 <br /> further delineated the petroleum hydrocarbon impacts at the site. TPH-DRO was <br /> detected in groundwater samples collected from all five monitoring wells. The <br /> distribution of TPH-DRO concentrations across the site(e.g. similar concentrations in <br /> the upgradient and downgradient wells),are indicative of a regional TPH-DRO issue. <br /> TPH-GRO, toluene, Y <br /> eth (benzene, xylenes, MTBE, TBA, and 1,2-DCA, were <br /> Y <br /> detected above their respective MDLs in groundwater samples collected from <br /> monitoring well MW-1 at concentrations generally consistent with previous results for <br /> the well. 1,2-DCA was reported at a concentration above the California Primary <br /> Maximum Contaminant Levels (MCL)in the groundwater sample collected from <br /> MW-1. <br /> Summary and Conclusions <br /> C <br /> The results of the recent site assessment are summarized below: <br /> • The 14 soil samples collected and analyzed were non-detect for <br /> petroleum hydrocarbons and oxygenates, with the exception of low <br /> detections of ethanol and methanol <br /> Page: <br /> CUam dis-usbfiicedata\Sacmmento-CAtENV1CHEVROM309075t6DeliverableslRepatsNssessmentM9075Assessment ReM_181810950.doc 8/10 <br /> i <br />