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Remo Canepa Page 6 of 9 <br /> d 6230 Pacific Avenue 4/17/2009 <br /> Stockton CA <br /> Canepas Car Wash MW3 <br /> 6230 Pacific Ave. <br /> 1DDD00 <br /> 10000 <br /> 10/5/05 <br /> 10/14/04 <br /> 1000 <br /> o N TPHg <br /> 00 MTBE E <br /> Slnne <br /> 8/1/96 4/21/99 <br /> U <br /> 10 <br /> 1/11/00 <br /> 1 <br /> 0. 1 — <br /> Monitoring Date <br /> MW-3, screened from 50 to 70 feet bsg , is located approximately 85 feet obliquely down- <br /> gradient of MW-1 . Groundwater monitored by this well is primarily impacted by MTBE, <br /> which had a fairly consistent concentration between 6. 3 and 18 ppb from August 1996 to <br /> July 2000, which then increased by more than two orders of magnitude up though <br /> October 2005 , reaching concentrations slightly less than those encountered in MW-1 ; <br /> since October 2005 the concentrations have been gradually declining . The increasing <br /> MTBE concentrations appear to represent migration of the main plume of dissolved <br /> MTBE, which may have already reached SV4 prior to July 1998, and certainly prior to <br /> July 2002, and may have been 'pulled' into MW-1 by GWE after November 2004. The <br /> EHD believes the MTBE concentration could represent a plume already in migration and <br /> not necessarily a new release. Again, the concentration trends do not match the profile <br /> utilized by R&B to confirm a second release at the Lahontan Region site. <br /> The discussion of butanes and pentanes provided by R&B did not provide sufficient <br /> information for the EHD to fully evaluate the significance of the occurrences of these <br /> compounds on the subject site other than stating the general concept that they normally <br /> would not be expected to be present in groundwater after a number of years. The EHD <br /> would be interested in the concentrations of the compounds in the various wells and <br /> their areal distribution , the concentrations normally encountered in known fresh releases, <br /> the decay, diffusion and dispersion rates of the compounds in the subsurface, etc. <br /> I <br /> During the review of site data for this evaluation , the EHD noted that the SVE wells are <br /> constructed in and near the dispenser area. EHD field notes indicate the SVE wells are <br /> screened from 5 to 45 feet bsg , but a general as-built diagram covering all the SVE wells <br /> indicates they are screened from 9 to 49 feet bsg ; both sources indicate that the filter <br /> pack is comprised of pea gravel . Intuitively, if the integrity of the well seal is <br /> Second Release Evaluation 0409 <br /> I <br />