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Chevron <br /> REO Chevron <br /> -FMH4 � <br /> JAN 2 U 1998 <br /> ENVIRC�(G%# 11= i �— A�-T i Chevron Products Company <br /> PRMI I / SE RVICIE <br /> 6001 Bollinger Canyon Road <br /> January 16, 1998 Building L <br /> San Ramon,CA 94583 <br /> P.O.Box 6004 <br /> San Ramon,CA 94583-0904 <br /> �• i <br /> Ms. Mary Meays Marketing—Sales West <br /> San Joaquin County Environmental Health Phone 510 842-9500 <br /> 304 E. Weber Ave., Third Floor <br /> i <br /> Stockton,CA 95202 <br /> Re: Chevron Station#9-4275, 2905 West Benjamin Holt Drive, Stockton, CA <br /> Attached Remediation Status Report(11/14/97) <br /> I <br /> Dear Ms. Meays:. <br /> I would like to acknowledge receipt of your letter dated December 29, 1997. Your letter provided <br /> comments to Geraghty&Miller's Corrective Action Plan,Blaine Tech's Third Quarter Monitoring <br /> Report,and discussed the need for-further corrective action. <br /> Chevron was requested to submit an addendum to Geraghty&Miller's Corrective Action Plan by January <br /> 15, 1998.It was stated that Chevron would be required to continue assessment of the evidenced plume. To' <br /> that extent, additional groundwater monitoring wells would be required to monitor groundwater <br /> conditions cross and down gradient from well MW-4. <br /> The plume in the vicinity of MW-4.ltas been represented by detections of MTBE. The second and third <br /> quarter 1997 sampling events detected increases of 3,600 and 2,100 ppb, respectively. These detections <br /> were not confirmed by GUMS analytical methods. The fourth quarter(November) 1997 sampling event <br /> however, detected only 54 ppb MTBE. The fourth quarter measurements were confirmed by GC/MS <br /> methods. The fourth quarter sample was.collected at the same approximate groundwater elevation where <br /> 2,100 ppb were detected during the third quarter.It is not known whether the observed concentration <br /> -decrease is a result of ongoing remediation effectiveness or whether it simply reflects inaccuracies of the <br /> two prior measurements. In light of these uncertainties, Chevron feels it would be premature to act on any <br /> trends in groundwater quality that haven't been confirmed. As a result,we do not agree with the need for <br /> further assessment. Instead, Chevron recoimnends continuing GC/MS analysis on all groundwater <br /> samples. The decision to further assess groundwater plume limits(and submit a CAP addendum)will be <br /> based on more accurately established trends. Your concurrence and patience.on this approach would be <br /> greatly appreciated. <br /> Your letter raised the issue regarding Geraghty&Miller's approach to calculating the current <br /> .hydrocarbon mass in place. When compared to the total mass in place, the amount represented by <br /> hydrocarbons dissolved in groundwater is insignificant. Knowing this, Chevron concurred with Geraghty <br /> &Miller's approach. As requested,Chevron will provide mass calculations in quarterly remediation status <br /> reports. <br /> Your agency also requested that Chevron re-sample groundwater at all site-related air sparge wells. The <br /> initial sampling was performed on April 1, 1997 in attempt to define the vertical extent of contamination <br /> Rerydble <br />