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` f f <br /> CH2M HILL <br /> 155 Grand Avenue <br /> Suite 1000 <br /> Oakland,CA <br /> CH2MHILL � DO 1 q <br /> ? 94812 <br /> y <br /> (� l 11 U P.O.Box 12681 <br /> Oakland,CA <br /> s4soa-zssi <br /> ..,�i, ,: <br /> October 16,2001 . `u�1?� :'c.'.`'�`�.''- � <br /> Tel 510.251.2426 <br /> Fax 510.893.3205 <br /> 131420.A1.09 <br /> Michael Infurna <br /> San Joaquin County Public Health Services z <br /> 304 E. Weber Avenue euwb 1 <br /> Third Floor <br /> Stockton,CA 95202 <br /> Subject: 110 Filbert Street,Stockton,California <br /> Modifications to Work Plan for Additional Investigation at the Disco Property <br /> Dear Mr. Infurna: <br /> The purpose of this letter is to inform you of modifications made to the work plan prepared <br /> by CH2M HILL on behalf of Del Monte Foods for performing additional site <br /> { characterization at the Disco Site (Site) on 110 Filbert Street Stockton,California. The work <br /> plan outlining additional cone penetrometer testing(CPT),monitoring well installation and <br /> extraction well installation was submitted to San Joaquin Public Health <br /> Services/Environmental Health Division(PHS/EHD) in December 2000. This Work Plan <br /> was approved,with conditions,in a January 2,2001 letter from the Central Valley Regional <br /> Water Quality Control Board. <br /> The CPT investigation was performed in August and September 2001. Groundwater <br /> samples were collected from CPT borings CPT-16 through CPT-24,installed at locations <br /> downgradient and cross-gradient of the 1,2-DCA plume(see attached figure). After review <br /> of the groundwater results from this investigation (see attached table) the proposed <br /> locations of the monitoring wells have been modified to better delineate and monitor the <br /> 1,2-DCA groundwater plume. These changes were made in agreement with Dot <br /> Lofstrum/PHS/EHD during meetings on July 11 and September 13,2001. The revised <br /> locations of the monitoring wells are presented in the attached figure. Four shallow <br /> monitoring wells (100 feet bgs) and one deep monitoring well (approximately 150 feet bgs) <br /> will be installed downgradient and cross-gradient of the Site. All shallow wells will be <br /> installed using hollow-stem auger drilling methods. The deep well,and associated <br /> conductor casing,will be installed using mud-rotary drilling methods. Please refer to the <br /> December 2000 work plan"for details regarding sampling and field methodology, the quality <br /> assurance project plan,and reporting. <br /> Rationale for the well locations are as follows: <br /> MW-DIS-11-This monitoring well will be installed at the location of CPT-12 to <br /> • monitor groundwater within the plume,downgradient of the source area. Data <br />