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RI Report, Volume V -2- 19 July 1991 <br /> DDRW, Sharpe Site <br /> believe that Sharpe has confused the definitions of saturation and transm ssivity <br /> and has used these terms interchangeably. Therefore, we do not concur with <br /> Sharpe's presentation of the site conceptual model . A clarification of the <br /> conceptual model will ultimately be needed in order to evaluate the remedial <br /> alternatives and to determine the appropriate remedial action for the unsaturated <br /> zone. <br /> Sharpe states that as long as the downgradient extent, morphologies and contaminant <br /> concentrations at the leading edges of the plumes are defined, the ground water <br /> remediation will be successfully accomplished. However, we are concerned that <br /> Sharpe has not clearly defined the lateral and vertical leading edges of all of the <br /> plumes. We believe that plume definition to background (non-detect forolatile <br /> organic constituents) is necessary in order to determine whether there is �omplete <br /> plume capture and hence, successful remediation of the plume. We are particularly <br /> concerned with this issue in the areas between plumes (for example: Plumes 1 and <br /> 3) where there are no monitoring wells to verify the presence or absence of the <br /> plume. We are also concerned that without better plume definition, such as in <br /> Plumes 4&5, 6 and 7&8, the remediation of the ground water may be unnecessarily <br /> lengthened. Better plume definition is needed to minimize the amount of potential <br /> unaffected ground water to be extracted for remediation. We believe that <br /> installation of additional monitor wells should occur during the Feasibility Study <br /> or during the remedial design phase and should be installed for verification of the <br /> effectiveness of the extraction system as well as for plume definition. However, <br /> Sharpe may elect to be conservative and design the extraction system to capture a <br /> larger area of ground water in lieu of further plume definition. <br /> Our approval of the RI Report is made in good faith that Sharpe will continue to <br /> address our concerns and comments which are made to optimize the cleanup of the <br /> soil and ground water contamination at the site. <br /> If you have any questions, please call Camilla Williams at (916)361-5670. <br /> ANTIAJ. VORSTER <br /> Senior WRC Engineer <br /> CKW:cw <br /> cc: Mr. John Hamill , U. S. Environmental Protection Agency, Region IX, San <br /> Francisco <br /> Ms. Tracie Billington, Department of Health Services, Region 1, Sac amento <br /> L,Mr. Fred Kaufman, Public Health Services of San Joaquin County, <br /> Environmental Health Division, Stockton <br /> Mr. Craig MacPhee, U. S. Army Toxic and Hazardous Materials lAgency, <br /> Aberdeen Proving Ground, Maryland <br />