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California-RegiAil iWateruality Control Board = : <br /> antral Valley egi<on <br /> Winston H.Hickox Sacramento Main ffice Gray Davis <br /> Secretnryfor lnternetAddress: htip:l/wvnv.swrc .ca.govlrwgcb5 Governor <br /> Environmental 3443 Routier Road,suite A,Sacramento,California 95827-3003 <br /> Protection Phone(916)255-3000•FAX{ t 6}255-3015 <br /> 28 December 2000 <br /> Ms. Lori Duncan <br /> Senior RENS <br /> San Joaquin County Environmental Health Division <br /> 304 East Weber Avenue <br /> Stockton, CA 95202 <br /> REVIEW CORRECTIVE ACTION PLAN, POMBO RANCH PROPERTY, 24100 SOUTH <br /> LAMMERS ROAD, TRACY, SAN JOA QUIN COUNTY <br /> Board staff reviewed the 31 March 2000 Corrective Action Plan (CAP) submitted by M. J. Kloberdanz <br /> &Associates (Kloberdanz) for the Pombo Ranch Property Kloberdanz used the EPA Bioscreen Natural <br /> Attenuation Decision Support System model to evaluate th e following four corrective action alternatives <br /> at this former UST site: <br /> 1. Low-risk site closure. <br /> 2. Excavation of source material. <br /> 3. Enhanced aerobic biodegradation(ORC injection). <br /> 4. Excavation of source material with enhanced aerobic biodegradation. <br /> As discussed in the attached staff memo, high concentrations of MtBE was identified in groundwater at <br /> the former UST area, monitoring wells have not been insto lled to adequately monitor groundwater <br /> contamination, modeling parameters including hydraulic conductivity, retardation, and solute haft-life <br /> have not been adequately assessed, and a sensitive receptor survey has not been completed. <br /> f <br /> Therefore, Board staff do not agree with the modeling con lesions presented in the C-AP. The <br /> C excavation of source material is the only alternative prese ted that will protect future beneficial uses—of <br /> groundwater at this site. Board staff recommend excavating the source material, installing a monitoring <br /> well network to adequately monitor groundwater contamination, and completing a sensitive receptor <br /> survey. <br /> If you have any questions or comments, please call me at ( 16) 255-3115. <br /> Marty Hartzell <br /> Associate Engineering Geologist <br /> Attachments <br /> California Environmental rotection Agency <br /> 00 Recycled Pape <br />