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Advanced <br /> GeoEnvironmental, Inc. - <br /> 29 November 2000 <br /> AGE-NC Project No. 98-0520 V <br /> n <br /> 1 <br /> Ms. Carol Oz <br /> SAN JOAQUIN COUNTY PHS-EHD <br /> 304 East Weber Avenue, 3' Floor �? <br /> Stockton, CA 95201 �r <br /> Subject: Additional Site Assessment Work Plan Addendum- November 2000 <br /> BOB'S MUFFLER SHOP <br /> 466 Moffat Road,Manteca, California <br /> Dear Ms. Oz: <br /> Results of the quarterly ground water monitoring event on 07 September 2000 indicated.that although the <br /> petroleum contaminant concentrations decreased in two wells,concentrations increased in two other wells, <br /> and the concentrations in one well remained the same. Pursuant to your letter dated 01 June 2000 and <br /> discussion on 27 November 2000, this work plan addendum provides specifics for the next phase of <br /> investigation, installation of three additional ground water monitoring wells. Methodology for monitoring <br /> well installation and sampling is described in the work plan prepared by Advanced GeoEnvironmental, Inc. <br /> (AGE)titled Preliminary Site Assessment Work Plan, dated 30 November 1998.However,in order to address <br /> the vertical extent of contamination at this site,AGE will bore one deep well adjacent to MW-5 (see Figure <br /> 2)to a depth of about 50 feet below surface grade(bsg), or deeper if detectable levels of organic vapors are <br /> found during field screening with an organic vapor meter.AGE proposes to set the screen depth between 45 <br /> and 50 feet bsg in this deep well, assuming a 50-foot TD. <br /> The changes to the work plan include the following: <br /> • Basing new well locations on the data collected during the quarterly ground water monitoring events, <br /> AGE proposes to install two wells to the west of MW-2 to help define the down-gradient lateral <br /> extent of contamination and one deep well adjacent to MW-5 to assess the vertical extent of <br /> contamination. A site map indicating the proposed new monitoring-well locations is attached(See <br /> Figure 2). <br /> • Quarterly monitoring of all of the wells until further directed by the PHS-EHD. In addition to the <br /> analytes listed in the previously approved work plan, ground water samples will be analyzed for <br /> ethylene dibromide(EDB)and 1,2-dichloroethane(1,2-DCA)by EPA Method 8260 as directed by <br /> the PHS-EHD. <br /> 4005 North Wilson Way,Stockton, California 95205 <br /> Telephone(209)467-1006 FAX(209)467-1118 <br />