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�CAMBRIA <br /> January 31, 2000 <br /> Ms. Lori Duncan <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, California 95202 <br /> Re: Response Letter/Work Plan <br /> Shell-branded Service Station <br /> 6131 Pacific Avenue <br /> Stockton, California <br /> © SAP Code9 <br /> Incident No.. 98996189 <br /> SJCPHS/EHD Site Code: 1223 <br /> Dear Ms. Duncan <br /> Cambria Environmental Technology, Inc. (Cambria) prepared this letter on behalf of Equiva <br /> Services LLC in response to the September 16, 1999 San Joaquin County Public Health <br /> Services Environmental Health Division (SJCPHS/EHD) letter requesting complete definition <br /> of the hydrocarbon plume at the above referenced site. This letter outlines our proposal for <br /> delineating the vertical and horizontal extent of petroleum hydrocarbons and methyl tertiary <br /> butyl ether (MTBE) in soil and groundwater beneath the site, and presents a work plan for <br /> site investigation activities. The scope of work presented in the work plan will comply with <br /> SJCPHS/EHD and Central Valley Regional Water Quality Control Board (RWQCB) guidelines. <br /> RESPONSE TO AGENCY ISSUES <br /> Several issues were mentioned in SJCPHS/EHD's recent letter. These issues are discussed <br /> below. <br /> Acceptable Detection Limit for MTBE: SJCPHS/EHD states in their letter that the <br /> acceptable limit for the detection of MTBE in water is 0.5 to 1.0 parts per billion (ppb). We <br /> contacted Sequoia Analytical Labs (Sequoia) to inquire about MTBE detection limits, as they <br /> Oakland, CA are the lab we typically use for groundwater analysis. They normally report MTBE by EPA <br /> Sonoma, CA <br /> Portland, OR Method 8020 at a detection limit of 2.0 to 2.5 ppb. When asked about a lower detection <br /> Seattle, WA limit for MTBE, they stated they could report MTBE results at a detection limit of 0.5 ppb <br /> with this method if requested to do so. We will request future groundwater analytical results <br /> Cambria <br /> Environmental for this site to be reported with a 0.5 ppb detection limit. <br /> Technology,Inc. <br /> Reducing Groundwater Analytical Procedures. As agreed to by SJCPHS/EHD, we will <br /> erkins Street <br /> P.O.Box 259 discontinue methanol and ethanol analysis for groundwater samples and perform analysis for <br /> Sonoma,CA 95476 <br /> Tel(707)935-4850 <br /> Fax(7o7)935-6649 <br />