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a <br /> Chevron <br /> Chevron <br /> Chevron Products Company <br /> February 28, 1997 6001'Bollinger Canyon Road <br /> Building L <br /> San Ramon,CA 94583 <br /> -P.O.Box 6004 <br /> San Ramon,CA 94583-0904 <br /> Ms.Mary Meays. Marketing—Sales.West <br /> San Joaquin County Environmental Health Phone 510 8424500 <br /> P.O.Box 388 <br /> Stockton, CA 95201-0388 <br /> Re: Chevron Station#9-0557, 139 South Center Street, Stockton,CA <br /> Attached groundwater monitoring report(Blaine Tech, 12/5/96) <br /> Dear Ms.Meays: - <br /> Please find attached a report dated December 5, 1996,which was prepared by Chevron's consultant, <br /> Blaine Tech Services Inc. (Blaine Tech),to describe the results of groundwater monitoring f" r`:'.i°; + <br /> performed at the.subject site on November 6, 1996. <br /> During their November site visit Blaine Tech gauged and sampled all seven site-related wells: <br /> Groundwater samples were analyzed for the presence of TPHGas;BTEX constituents,and MTBE.In . = <br /> addition, all seven wells were sampled for various parameters relating to the evaluation of intrinsic <br /> bioremediation potential. The measured direction of groundwater flow beneath the subject s to was <br /> toward the southeast. This is consistent with historic trends.Dissolved petroleum hydrocarbons and <br /> MTBE were detected at wells MW-21 MW-5,and MW-7;The measured concentrations were consistent <br /> with recent detections. There were no dissolved hydrocarbons or MTBE reported at wells-MW-1,MW-3, <br /> MW-4,.and MW-6. <br /> The screened intervals of all site-related:wells have:mostly been submerged since 1995. The dissolved <br /> hydrocarbon concentrations measured since alien may not be entirely representative of groundwater <br /> conditions. However;there were several noticeable trends established-prior to the.screens.becoming <br /> submerged. For example,the groundwater flow direction was consistently to the southeast. The levels of <br /> dissolved hydrocarbons measured at wells MW-3 and MW-4 were non-detect. The detectable <br /> concentrations measured at wells MW-1,MW-2,MW=5,and MW-6 were either decreasing or were <br /> relatively stable. These trends indicate the dissolved.hydrocarbon plume is stable and is:riot rrugrafiiig: <br /> Considering this information along with recent groundwater data; Chevron proposes the.following' <br /> modifications to the groundwater monitoring and reporting program currently in effect: <br /> -Gauge and sample wells MW-1,MW=2,MW-5,MW-6;and MW-7 semi-annually'(1stQ;4thQ)-: <br /> -Discontinue monitoring wells MW-3 and MW-4 ` <br /> i <br /> -Analyze all samples for TPHG;BTEX,and MTBE <br /> -Report monitoring results annually;discontinue reporting potentiometric surface maps <br /> The proposed modification would result in a program that allows effective evaluations of groundwater <br /> conditions_to continue and would provide the information in the most cost effective manner. Subsequent <br /> tire, Reoyckd <br /> Vii. Ra:ys;t,abie - <br />