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HOLGUIN, FAHAN & ASSOCIATES, INC. <br /> ENVIRONMENTAL MANAGEMENT CONSULTANTS <br /> September 30, 2009 RECENEDD <br /> OCT 01 2009 <br /> Ms. victoria L. McCartney, REHS ENVIRONMENT HEALTH, <br /> PERMIT/SERVICES <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street <br /> Stockton, California 95202 <br /> Subject: SITE CONCEPTUAL MODEL AND FEASIBILITY STUDY FOR <br /> CHEVRON FORMER SERVICE STATION #9-0557 <br /> 139 SOUTH CENTER STREET, STOCKTON, CALIFORNIA <br /> (SJCEHD CASE #1039) <br /> Dear Ms. McCartney: <br /> On behalf of Chevron Environmental Management Company (Chevron), Holguin, Fahan & <br /> Associates, Inc. presents two reports, a site conceptual model and a feasibility study, for the <br /> above-referenced site. The site conceptual model and results from three site-specific feasibility <br /> tests were utilized to evaluate potentially applicable remedial technologies to mitigate the <br /> constituents of concern beneath the site. The feasibility study concludes that monitored natural <br /> attenuation (MNA) is a feasible remedial alternative to meet remedial objectives because the <br /> groundwater hydrocarbon plume is stable to shrinking, no human health risks or ecological risks <br /> are present, and feasibility testing indicates that activeremedial remedial alternatives would not be <br /> cost-effective. Therefore, MNA is the most cost-effective remedial alternative consistent with <br /> California Resolution 2009-0042, based on technical impracticability of active remedial <br /> alternatives to more effectively achieve groundwater ESLs. <br /> If the San Joaquin County Environmental Health Department concurs with MNA implementation, <br /> HFA will prepare a monitoring plan. The plan would include sampling and analysis for indicators <br /> of biodegradation (DO, ORP, alkalinity, etc.) and continued monitoring of plume stability. <br /> i <br /> ENVIRONMENTAL SCIENTISTS GEOLOGISTS ENGINEERS <br /> Contaminated Site Assessment • Fixed & Mobile Remediation • Project & Program Management <br /> Ventura, CA Pleasanton, CA Redlands, CA Tempe, AZ Flagstaff, AZ <br /> 805-641-1056 800.672-0219 909-793-4571 480-505-3332 928-779-5447 k <br /> http://www.hfa.com i <br />