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1444 MARIPOSA ROAD <br /> WKA No. 2938 07 <br /> January 18,2001 <br /> Page 4 <br /> through MW3 are screened deeper than MW4 through MW7 provides the opportunity to <br /> examine the vertical migration of MTBE. Since the migration of this fuel oxygenate has become <br /> a hot button issue with regulatory agencies, it is fortunate that data is available from the deep <br /> water zones. <br /> With this in mind, MTBE has been discovered in wells MW2, MW3, and possibly MW4. In <br /> addition,Tert-Butanol, which may be a breakdown product of MTBE,has been additionally <br /> reported in wells MW2,MW4 and MW7. All of the above oxygenates were reported in trace <br /> concentration well below even taste and odor thresholds limits. And because the presence of <br /> these oxygenates has been intermittent in wells MW2 and MW3, it is our opinion that we have <br /> identified the vertical extent of any oxygenate migration. Additionally,the lateral extent of <br /> MTBE migration appears to have been identified because it has only been recorded in two <br /> perimeter wells (MW3 m June and December of 1999 and MW4 in June of 1999) The highest <br /> of these perimeter concentrations was 0.81 ugA The MW4 result referred to above was only <br /> 0 01 ug/l over the detection limit, so that it is unclear as to weather this reported concentration <br /> • was actually a hit. <br /> Given that these trace concentrations are all that are present in the perimeter wells 11 years after <br /> the tanks were removed and 9 years after the vast majority of contaminated soil was excavated <br /> and aerated, it appears that both natural attenuation and biodegredation have been acting on any <br /> residual contaminants. The natural reactions, along with the proactive remediation, appear to <br /> have reduced the threat of further contgmination to a negligible point and also appear to <br /> demonstrate that any remaining contamination is at the very Ieast, stable. <br /> During our previous well survey and review of the California Department of Water Resources <br /> well construction records we confirmed the existence of 51 wells within a 2,000-foot radius of <br /> the site. The wells were identified either through review of well construction records,windshield <br /> survey or interviews. The nearest well to the site is located at the El Camino Motel,which is <br /> located at 1506 ManyogL This well is approximately 350 feet south of the southern property <br /> boundary. This well was discovered during a windshield survey. No records(boring log or well <br /> construction details) of the well were revealed during our record search at the Department of <br /> Water Resources. According to the motel manager and maintenance manager for the motel,the <br /> total depth of the well is approximately 60 feet and has been in use for at least 22 years. They <br />