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'POP <br /> TOSCO_ <br /> Marketing <br /> C o m p a n y - <br /> February 3, 1999 <br /> Ms. Margaret Lagorio <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 E. Weber Avenue, Third Floor <br /> Stockton, CA 95202 <br /> Tosco (Former Unocal) #6981 (Site Code 1217123) <br /> 4707 Pacific Avenue <br /> Stockton, CA <br /> Ms. Lagorio: <br /> This letter was prepared in response to your letter of January 8, 1999 to Unocal's Peter <br /> Niemiec, requesting a work plan to define the vertical extent of the soil and groundwater <br /> contamination and evaluate the effectiveness of the vapor extraction system at this site. <br /> Your letter directed Unocal to implement a specific scope of work and specified locations <br /> for additional monitoring wells and soil borings at the site. Tosco previously submitted <br /> Gettler-Ryan Inc.'s (GR) Work Plan For Soil Boring And Monitoring Well Installation <br /> (dated September 12, 1997) that proposed installation of one downgradient monitoring <br /> well and one soil boring near well VW-2. <br /> In respect of your request to Unocal, and in the interest of maintaining a good working <br /> relationship with San Joaquin County Public Health System (SJCPHS), Tosco has <br /> requested GR to prepare an Addendum for implementing the directed scope of work. <br /> As requested in your letter, this Addendum will propose additional soil borings adjacent <br /> to wells MW-2 and MW-5. Well casings will be installed in one of these borings if field <br /> screening indicates that hydrocarbon impact might extend to depths lower than wells <br /> currently installed at the site. The Addendum will also propose that a well be <br /> constructed in the boring drilled downgradient of existing wells MW-2 and VW-4, and <br /> this well will be screened across the existing water table. The well previously proposed <br /> for the east side of Pacific Avenue (downgradient of the site) will also be screened <br /> across the existing water table. Finally, the Addendum will contain a contingency for <br /> installation of air sparge wells if field observations warrant. <br /> Tosco has also directed GR to commence semi-annual sampling of PTW1 and evaluate <br /> the current radius of influence for the vapor extraction system, during the first quarter <br /> 1999. <br /> Your request for information regarding dates of operation (prior to June 1988) of the <br /> UST system are not readily available. We are advised that Unocal purchased the <br /> 1380 Lead Hill Road <br /> Suite 120 <br /> Roseville, CA 95661 <br /> 916.774.2910 <br /> fax: 916.774.3004 <br />