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t <br /> moi= 2000 Crow Canyon Place <br /> Suite 400 <br /> - San Ramon, CA 94583 <br /> IPOP -95.277.2305 <br /> ' _ fax: 925.277.2361 <br /> r M, Environmental <br /> T��+C 0 - 2 Obompliance <br /> Department <br /> M a r k e t i ng <br /> Company <br /> June 1, 1999 <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> Mr. Michael Infurna <br /> 304 East Weber Avenue,Third Floor <br /> P.O.Box 388 <br /> Stockton,CA 95201-0388 <br /> RE: Tosco Facility#11192 <br /> 1403 County Club Blvd. <br /> Stockton, California <br /> Dear Mr.Infama: <br /> This letter responds to the May 14, 1999 letter you received from BP Oil Company'concerning the status of <br /> case closure for the referenced facility. Based on recent correspondence and groundwater monitoring <br /> results,BP Oil Company believes case closure is warranted and that rising MTBE levels detected in <br /> groundwater are associated with a more recent release during Tosco's operation of the site. Additionally, <br /> the San Joaquin County Public Health Services(SJCPHS)issued an.Unauthorized Release(Leak)Report <br /> on January 7, 1999 in response to rising MTBE concentrations and have named Tosco Marketing Company <br /> as the responsible party. Tosco has several-concerns and comments regarding these issues that we wish to <br /> bring to your attention. <br /> As you know,site investigation has been underway by BP Oil Company since at least 1989 or 1990 when <br /> they assumed operation of the station following Mobil's tenancy. To date,seven groundwater monitoring <br /> wells(MW 1 through MW7)have been installed onsite. The groundwater plume remains undefined. <br /> Although a SVE system was installed in 199.1 and SVE pilot test was conducted in 1992,Tosco does not <br /> have any records that the SVE system was ever operated. <br /> Tosco is not convinced that recent observations noting rising MTBE concentrations,particularly in well <br /> MW3,are proof a release during Tosco's tenancy. We would like the SJCPHS to note the following: <br /> • It does not appear that MTBE concentrations have been corroborated using EPA Method 8260 <br /> analyses. It is Tosco's understanding that MTBE detections can be falsely reported,particularly with <br /> elevated TPHg concentrations. Tosco believes it appropriate to confirm MTBE using EPA Method <br /> 8260. <br /> • There is a strong correlation between increases in TPHg/MTBE concentrations in early 1998 and rising <br /> groundwater elevation as demonstrated in the attached figure for well MW3. Groundwater•was <br /> encountered at 22 feet below grade during installation of well MW3 in April 1990. The current depth <br /> to groundwater in this well,based on the January 1999 monitoring event,was at approximately 13 feet <br /> below grade,a rise of almost nine feet. 1998 and 1999 elevation data represent historical groundwater <br /> highs in this well,which coincidentally,correspond to historical high MTBE concentrations. <br /> © 76 <br /> Brown Bear <br /> —71 Car Wash <br />