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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> Donna K Heran,R-E.H.S. 304 East Weber Avenue, Third F100I' Carl Borgman,R.E.H.S. <br /> Director Mike Huggins,R.E.H.S.,R.D.T. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 - Douglas W.Wilson,R.E.H.S. <br /> • Cq -_ ;p.� Program Manager. Telephone: (209) 468-3420 - -Margaret <br /> Laurie A.Cotulla,R.E.H.S. ` 'Robert McClellon,R.E.H.S. <br /> Program Manager Fax: (209)464-0138 Mark Barcellos,R.E.H.S. <br /> DARIN ROUSE SEP 0 3 2003 <br /> EXXONMOBIL REFINING AND SUPPLY COMPANY <br /> PO BOX 4032 <br /> CONCORD CA 94524-4032 <br /> RE: Former Exxon Retail Site 7-3942 SITE CODE: 2231 <br /> 4444 North Pershing Avenue <br /> Stockton, CA <br /> San Joaquin County Environmental Health Department (EHD) is the lead agency providing the <br /> oversight of the investigation and cleanup of releases from underground storage tanks <br /> (UST) within San Joaquin County. EHD has a contract with California State Water <br /> Resources Control Board (SWRCB) to conduct an UST corrective action program. <br /> EHD has completed reviewing the Feasibility Study and Work Plan for Well Installation <br /> submittal prepared by ETIC on behalf of Exxonmobil and has the following comments: <br /> 1. The deep monitoring well (MW) proposed off site to define the vertical extent <br /> of soil and groundwater contamination in the down gradient flow direction is <br /> approved in concept. Please submit a well permit application, a Work Plan <br /> (WP) , and an $89.00 fee for EHD review and permit issuance. When the permit <br /> is issued, well installation can begin. <br /> 2. MWs SW-1 and SW-2 are in the area of the unauthorized release on site. They <br /> have well screens from 40-45 feet bgs and have evidenced ground water <br /> contamination approximately 20 feet below the current static water table. <br /> These MWs have been recently added to the sampling schedule and should remain <br /> on a quarterly monitoring and sampling schedule. To define the vertical extent <br /> of contamination in the source area, a deep ground water investigation is <br /> required to define the limits of contamination. <br /> 3. The adsorbed or dissolved contaminant masses for soil or ground water have not <br /> been estimated. When the vertical limits in soil and ground water <br /> contamination have been defined, you are required to calculate and report <br /> these contaminant masses. To date, only remediation system removal mass has <br /> been reported, but the estimated residual mass has not. <br /> 4. Due to the apparently large contaminant mass caused by the unauthorized <br /> release and the high contaminant concentrations in ground water, EHD cannot <br /> approve passive remediation, or natural attenuation, as the remedial choice <br /> for corrective action at this site. Passive natural attenuation will not <br /> restore groundwater quality in a reasonable amount of time. Therefore, L'.'7 <br /> - recommends an active remedial technology for corrective action. END recommends <br /> a pilot study be conducted to evaluate low-flow rate ozone sparging at this <br /> site. The study should also evaluate contaminant migration and/or destruction <br /> and any modification of ground water flow direction as a result of the ozone <br /> sparing. <br /> If you have any further questions regarding this matter, please contact Harlin Knoll at <br /> (209) 468-3442. <br /> Donna Heran, REHS, Director <br /> Environmental Health Division <br /> Harlin Knoll, Senior REHS Nuel C. Henderson ttl <br /> LAP/Site Mitigation Unit IV LOP/Site Mitigati nbi t`IV {) <br /> cc: WOCB-James L. L. Barton <br /> TIC-Ted Moise !t ? SEP 1 203 !! <br /> Bank of Stockton-Rick Correia <br /> L- <br /> Brooke Burkie - L _ <br />