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V <br /> Advanced <br /> GeoEnvironmental, Inc. <br /> 27 August 2002 <br /> AGE-NC Project No. 95-0142 <br /> Mr. Harlin Knoll <br /> San Joaquin County Environmental Health Department AUG 2 g ZOOZ <br /> 304 East Weber Avenue, 3`d Floor <br /> Stockton, CA 95202 ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <br /> Subject: Ground Water Extraction Clean Up Analysis <br /> FORMER STOCKTON PLATING FACILITY <br /> 632 South E1 Dorado Street, Stockton, California <br /> Dear Mr. Knoll: <br /> At the request of Mr. Richard Leland, Advanced GeoEnvironmental Inc. (AGE) has prepared the <br /> following analysis of the proposed remediation technology for the above referenced site in response <br /> to the San Joaquin County — Environmental Health Department (EHD) letter received in August <br /> 2002. Ground water extraction and soil vapor extraction have been proposed for the site by AGE in <br /> the Final Remediation Plan, dated 23 April 2002. <br /> AGE submitted a Corrective Action Plan (CAP) for the site on 15 November 1995. At that time, <br /> AGE stated that in-situ air sparging (1AS) would be more effective in remediating the ground water <br /> than a pump and treat ground water extraction system, based on the information procured during a <br /> limited six-month assessment of the site. At the time the 'CAP was prepared, contaminant <br /> concentrations were thought,to be low [benzene less than 1,000 micrograms per Iiter (µg/1)], the <br /> vertical extent of impacted ground water was not required and the remediation of methyl tertiary <br /> butyl ether(MTBE)was not required. <br /> Since that time, the ground water elevation has risen significantly and has maintained an elevation <br /> of approximately 25 feet bsg, 20 feet higher than the ground water elevation in November 1995. <br /> The current concentration of benzene is over 30,000 ug/I, as determined from well samples within <br /> the former UST area. Currently MTBE has been vertically defined in the former UST area, <br /> however, the MTBE plume has migrated at least 80 feet downgradient and has been detected at a <br /> depth of 70 feet below surface grade in samples from MW7. At the time of the CAP preparation, <br /> the lateral extent of the hydrocarbons in the soil and ground water was defined. However, at that <br /> time, the vertical extent of the impacted soil was reported to extend to ground water. <br /> �r <br /> 837 Shaw Road,Stockton,California 95215 <br /> Telephone(209)467-1006 FAX(209)467-1118 <br />