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could migrate into deeper aquifers, and we consider the possibility of vertical migration very <br /> remote. It is difficult to conceive of a reasonable scenario in which contaminants bypassed the <br /> shallow aquifer and migrated downward to deeper zones. Further, our experience at other sites has <br /> shown that when MTBE is present in the groundwater, the highest concentrations occur at the water <br /> table in the first aquifer, and concentrations decline downward through that aquifer. Concentrations <br /> in deeper aquifers are lower still, and other analytes (TP11-g, benzene) are nonnally below the <br /> detection limit. This downward attenuation of concentrations is predictable; extraordinary <br /> circumstances would be required to produce the opposite trend. <br /> Within the past two years, DID and the Regional Water Quality Control Board have requested Mr. <br /> Peters to test groundwater samples for the presence of lead, gasoline oxygenates, and 1,2-DCA and <br /> to prepare a comprehensive and detailed conceptual model of the site. These requests have been <br /> met and the results have substantiated the interpretation that groundwater beneath the site became <br /> contaminated prior to the 1990's due to release of gasoline from the former Chevron site at 2103 <br /> Country Club Boulevard and subsequent eastward migration. Contamination reached a peak prior <br /> to 1995, and has been steadily diminishing since that time. Remediation accelerated frorn 2001 to <br /> early 2003 during the operation of a groundwater remediation system at the Chevron site, which <br /> largely contained the contaminant plume and prevented further migration of contaminants to the <br /> east. Now that remediation has ended (at least temporarily) at the Chevron site, it is possible that <br /> eastward migration may resume; however, such spread of contaminants is the responsibility of <br /> owners of the property where the plume originated, not the owners of downgradient properties. <br /> Therefore, v%-e again request EHD and the Water Board to close the investigation and issue a No <br /> Further Action Letter to Mr. Peters. <br /> 6 <br /> • <br />