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. r a <br /> PUBLIC IqEALTH SERVICES <br /> ApU1N <br /> �. •.o <br /> SAN JOAQUIN COUNTY ;Z <br /> z� <br /> ENVIRONMENTAL HEALTH DIVISION y <br /> Ernest M. Fujimoto, M. D., M.P.H., Acting Health Officer <br /> 304 E. Weber Ave., Third Floor • P. O. Box 388 * Stockton, CA 95COO F6 <br /> 10", <br /> 209/468-3420 <br /> BRETT HUNTER OCT <br /> d 4 1996 <br /> CHEVRON USA <br /> P 0 BOX 5004 <br /> SAN RAMON CA 94583-0804 <br /> RE: Ron's Chevron SITE CODE: 1039 <br /> 139 South Center, Stockton CA 95202 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> completed review of the "Work Plan for Well Installation" dated September 26, 1996 <br /> which was prepared by Pacific Environmental Group. PHS/EHD has the following <br /> comments for your consideration. <br /> The work plan proposed to install one monitoring well, MW8, downgradient of MW7 in <br /> hopes of defining the extent of the 350 ppb benzene groundwater contamination <br /> evidenced in the most currently downgradient well, MW7. The work plan also proposed to <br /> perform a well survey and to research other potential nearby off site sources. <br /> PHS/EHD has directed Chevron since August 23, 1991 to install any additional wells <br /> necessary to define the extent of groundwater contamination. PHS/EHD indicated in <br /> correspondence dated March 17, 1992 that the extent of groundwater contaminated must <br /> be determined. In response, MW5 was installed on November 4, 1992 which <br /> subsequently evidenced groundwater plume migration. PHS/EHD indicated in <br /> correspondence dated March 25, 1993 that the extent of groundwater contamination must <br /> be determined. In response, MW6 was installed on September 14, 1993. Prior to the <br /> elevation of the groundwater table above the screened interval August 1995, groundwater <br /> contamination was detected up 130 ppb benzene in MW6 since its installation. PHS/EHD <br /> indicated in correspondence dated February 28, 1994 that it would be likely that additional <br /> monitoring wells would be necessary to define the extent of groundwater contamination. <br /> Based on monitoring results, PHS/EHD indicated in correspondence dated September 6, <br /> 1994 that additional groundwater investigation was necessary. In response, MW7 was <br /> installed on December 1, 1995. PHS/EHD directed in correspondence dated December 13, <br /> 1995 that all additional investigation necessary to define the extent of soil and <br /> groundwater contamination be completed prior to May 1, 1996 and that feasibility studies <br /> necessary to prepare a corrective action plan be included with the final investigative phase. <br /> The historical record indicates Chevron has submitted minimum scopes of work and that <br /> over four years have been spent in tentative efforts to define the extent of groundwater <br /> contamination. <br /> Please note that an amended work plan should be submitted within 14 days of the date of <br /> this letter that proposes a scope of work that will complete the groundwater and soil <br /> A Division of San Joaquin County Health Care Sen-ices <br />