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i <br /> C,eologicaI Technics 14c. Page 3 <br /> Cardoza <br /> Project No. 662.2 <br /> March 26,2003 <br /> Response: Two GeoProbe borings, GP-1 & GP-2, were installed to depths of 33 <br /> and 31 feet below grade surface (bgs), respectively, in 1998. Soil samples from <br /> these borings revealed the presence of MTBE at concentrations ranging 0.0079 - <br /> 0.11 mg/kg at depths of 16 — 29 feet bgs. These samples were obtained before <br /> monitoring wells MW-1 through MW-3 were installed in 2000 indicating that <br /> vertical migration to a depth of 29 feet was not due to the installation of these <br /> wells. Since the low permeability zones identified by the continuous sampling of <br /> boring MW-104 have not been proven to be laterally continuous across the site, <br /> GTI believes that abandoning these wells is premature, especially since MW-2 has <br /> continued to be non-detect and defines the northwest extent of the plume. GTI <br /> a included the replacement of the wells in the work plan based on the <br /> "recommendations" of SJC PHS/EHD for reasons stated above. <br /> { 4. 11/18/02- "...it may be more cost effective to place a single casing, multi <br /> chambered, polyethylene-type monitoring well in a single bore hole (nested) than <br /> to place five single screened PVC casing monitoring wells in separately drilled <br /> boreholes (clustered). " <br /> � 2/14/03- "EHD concurs that offsite monitoring wells are needed, but opts to <br /> withhold approval for the use of the CMT/multi-chambered, single casing well <br /> type until the CPT data and site conceptual model can justify this expense. Please <br /> support or modify the unapproved tasks contained in this workplan... " <br /> Y <br /> Response: In our letters SJC PHS/EHD has denied GTI's proposed placement of <br /> P <br /> discrete PVC monitoring wells offsite and denied placing multi-chambered wells <br /> offsite. We are not sure exactly what you do want. It is a good plan to obtain <br /> geologic information from the CPT boreholes prior to installing further offsite <br /> wells. In the report of the CPT results, we will provide recommended locations <br /> and construction of selected offsite wells. To shorten the iterative letter writing <br /> campaign we seem to be in during the last two. years, we request that SJC <br /> PHS/EHD determines which well construction method they will approve for the <br /> offsite wells (i.e., multi chambered wells or well clusters) and we will include that <br /> in our plan for these wells after the CPT work is complete. <br /> F` <br /> E <br /> t <br /> j 1 <br /> 1 1 <br />