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v %.O� <br /> Stantec Consulting Corporation <br /> Adat 290 Conejo Ridge Avenue <br /> Thousand Oaks,CA 91361 <br /> Tel:(805)230-1266 <br /> Fax:(805)230-1277 <br /> Stantec ,P <br /> May 14, 2010 <br /> Stantec File No. 211302645 <br /> Mr. Michael Infurna <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street <br /> Stockton, CA 95202 <br /> Reference: Request for Low-Risk Case Closure <br /> Former 76 Service Station No. 5886 <br /> 2701 West March Lane <br /> Stockton, California <br /> SJCEHD Site Code: 1176 <br /> Dear Mr. Infurna: <br /> On behalf of ConocoPhillips Company, Stantec Consulting Corporation (Stantec) is requesting low- <br /> risk case closure for the above-referenced site (Figures 1 and 2). As is stated in a draft resolution <br /> prepared by the State Water Resources Control Board (SWRCB) in response to SWRCB <br /> Resolution No. 2009-0042: <br /> "...a UST case should be closed not only where cleanup goals and objectives are <br /> currently met, but also where they will be met in a reasonable period. Further, what <br /> constitutes a reasonable period must be based on an analysis of all relevant factors <br /> including, but not limited to, where the residual contamination poses a threat to <br /> human helath or safety and is localized and unlikely to migrate beyond the current <br /> spatial extent, and if the affected groundwater will be used as a source of drinking <br /> water or other designated beneficial use in the timeframe required to meet cleanup <br /> goals and objectives"(a copy of this text is included as Attachment 1). <br /> Stantec feels the conditions at the above-referenced site meet these conditions. The bases for the <br /> request are the following: <br /> o The suspected source-zone hydrocarbon impacted soil has been excavated, and no soil <br /> samples collected since then (1996) have contained hydrocarbon concentrations which <br /> exceed their respective California Regional Water Quality Control Board — San Francisco <br /> Bay Region (CRWQCB-SFBR) final Environmental Screening Levels (ESLs) for either <br /> commercial or residential land use; <br /> o On-site groundwater impact appears to have been sufficiently remediated through the use of <br /> an ozone sparge system. Off-site groundwater impact appears limited to methyl tert-butyl <br /> ether (MTBE) observed in the vicinity of well cluster MW-9. As documented in Stantec's <br /> Results of Hydrogeologic Modeling, dated January 6, 2010 (included as Attachment 2), off- <br /> site MTBE impact is expected to attenuate over time, and not expected to significantly <br /> migrate down-gradient; <br /> o A review of historical groundwater analytical data indicate that other than MTBE <br /> concentrations detected in well MW-3 between first quarter 1999 and second quarter 2000 <br /> (at concentrations ranging from 31,000 micrograms per liter [Ng/L] to 122,000 pg/L), no <br />