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CH2M HILL <br /> 1111 Broadway <br /> ' Suite 1200 - <br /> ® <br /> Oakland, <br /> �k; IdT ^t rig".I-ifr <br /> -C0. <br /> CH2MHILL t00 F( 7 04607-4046 <br /> Gni U 39. FO Box 12661 <br /> Oakland,CA <br /> February 3,2000 94604-2681 <br /> Tel 510.251.2426 <br /> 131420.Al.08 Fax 510.693.6205 <br /> Proud Sponsor of <br /> National Engineers Week 2000 <br /> Ronald Rowe <br /> San Joaquin County Public Health Services <br /> LOP/Site Mitigation Unit <br /> Environmental Health Division <br /> 304 E.Weber Ave.,Third Floor . <br /> Stockton,CA 95202 <br /> Subject: Disco Site <br /> 110 Filbert Street,Stockton Califorriia . . <br /> Dear Mr. Rowe: <br /> Attached are the latest results for the groundwater samples collected from the Disco site, <br /> located at 110 Filbert Street,.Stockton,California.A site map showing the latest boring <br /> locations is also included. <br /> Borings CPT-6,CPT-7,and CPT-8 were installed on Highway 4,south of the Disco site <br /> (Highway 4 is approximately 25 feet below the grade of the site). Hydrocarbon } <br /> concentrations in groundwater samples from borings CPT-7 and-8 are an order of <br /> .magnitude less than those found onsite,:however, they are still high.CPT-7 and-8 are more <br /> directly downgradient than CPT-6,which may explain the lower concentrations found in <br /> CPT-6. Further, the sand layer found beneath the site between 90 and 100 ft bgs was found <br /> in borings CPT-7 and-8,but was much thinner,and it was not found in CPT-6.Nonetheless, <br /> the results indicate we have a larger hydrocarbon.pluxne than anticipated.. <br /> The low concentrations of hydrocarbons found in the deeper samples in CPT-7 and-8 are <br /> likely attributed to sampling contamination,as these concentrations are similar to those <br /> found in Equipment Blank-1.The thick,fine-grain layer underlying the impacted zone <br /> appears continuous and should act as an excellent barrier to downward migration: <br /> The 1,2-DCA is prevalent,and is a concern.As we see in other sites,when EDB and 1,2-DCA <br /> are found in a source area,EDB is usually not found very far downgradient,but 1,2-DCA <br /> commonly is. <br /> I have discussed these results with Del Monte,and we propose to return to the site to collect <br /> more groundwater samples,further downgradient.Potential boring locations are shown on <br /> the attached figure.We propose to install 4 additional.CPT borings on the south side of <br /> Highway 4,and shall collect at least 2 groundwater samples from each boring. One <br />