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. 06 September 2002 <br /> AGE Project No 95-0130 <br /> Page 4 of 4 <br /> Based on the significant MTBE concentrations reported at the Top Filling Station and the apparent <br /> trend of Increasing MTBE concentrations reported at the Rock Property, AGE recommends that <br /> Interim ground water remediation should be Implemented at the Top Filling Station site in <br /> Hydrologic Unit 1 (30 feet to 55 feet bsg) Utilization of an interim pump-and-treat technology in <br /> Hydrologic Unit 1 would serve to Inhibit further migration of MTBE-Impacted ground water off-site <br /> (Implement hydraulic control),would Immediately reduce the mass of the existing plume,and would <br /> provide immediate relief and protection for the municipal drinking water well located only 900 feet <br /> toward the east-southeast (Cal-Water Station No 40) of the site <br /> Due to the well-defined, laterally continuous, sandy nature of Hydrologic Unit 1,it would appear to <br /> be advantageous to Implement an Interim ground water pump-and-treat system screened solely <br /> through Hydrologic Unit 1 Furthermore,due to the unfavorable hthology change between the vadose <br /> zone (less permeable silts and silty sand) and Hydrologic Unit 1 (more permeable fine to medium <br /> sand),in-situ air sparing will probably not be an effective interim remediation alternative to address <br /> Hydrologic Unit 1 due to the potential for air flow channeling <br /> If you have any questions or require further information,please contact our office at(209)467-1006 <br /> Sincerely, Do7327 <br /> Advanced GcoEnvironmcntal, Inc. =A <br /> Timothy C lar Calvin F Lee ®F CP•�� <br /> Project Geologist Senior Project Geologist <br /> Registered Geologist No 7327 <br /> Enclosures <br /> cc Mr Ed Endich, Top Filling Station <br /> Mr Marty Hartzell, Regional Water Quality Control Board - Central Valley Region <br /> Advanced GeoEnvironmental,Inc <br />