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• MEMORANDUM . <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A Phone: (916) 255-3000 <br /> Sacramento, CA 95827-3098 CALNET: 8-494-3000 <br /> TO: Antonia K. J. Vorster FROM: James Taylor <br /> Senior WRC Engineer Associate Engineering Geologist <br /> DATE: 17 May 1993 SIGNATURE: <br /> SUBJECT: 1992 ANNUAL PROGRESS REPORT, GROUNDWATER MONITORING PROGRAM, DEFENSE <br /> DISTRIBUTION REGION WEST (DDRW), SHARPE, SAN JOAQUIN COUNTY <br /> I have reviewed the 1992 Annual Progress Report submitted on 16 March 1993 for DDRW, <br /> Sharpe. This document was prepared by DDRW, Sharpe Environmental Protection Office. <br /> Overall the Report was well prepared. My comments on the above referenced submittal <br /> are discussed below. <br /> 1. The Annual Report recommends sampling frequencies for monitoring wells. <br /> Changes from the current monitoring frequency per well , and the rational <br /> supporting the proposed changes were not presented in the Annual Report. A <br /> brief narrative description of proposed changes in the sampling frequencies <br /> with the supporting rational must be included in the Annual Report. <br /> 2. The Annual Report indicates that NA-7 will continue being used as an extraction <br /> well . Use of this well should be discontinued because the contaminant <br /> concentrations are below the aquifer cleanup levels (the Primary Maximum <br /> Contaminant Level (MCL)) . In our letter dated 26 June 1992, we stated that use <br /> of this well should be discontinued. The concentrations of trichloroethylene <br /> (TCE) , tetrachloroethylene (PCE) or any other volatile organic constituent <br /> (VOC) has been below the respective aquifer cleanup levels since installation. <br /> The continued use. of this extraction well may only serve to exacerbate the <br /> plume extent. Extraction wells are not needed in areas where the contaminant <br /> concentrations ares below the aquifer cleanup levels. Unless the concentration <br /> increases above the Primary MCL for TCE, this well should not be used for <br /> extraction. <br /> DDRW, Sharpe should continue to monitor the concentrations in the extraction <br /> wells in the South and North Balloon Areas. Extraction wells which have <br /> concentrations below the aquifer cleanup level for a minimum of two quarters <br /> may be considered for temporary discontinuation of extraction. Use of the <br /> extraction wells which have concentrations below 5 Ag/l for TCE should not be <br /> permanently discontinued as these wells may again be required for the cleanup <br /> of other VOCs which remain above the aquifer cleanup level . The criteria for <br /> determining when use of an extraction well should be discontinued or when it <br /> should be returned to service should be discussed among the Project Managers. <br /> DDRW, Sharpe should have the concurrence of all of the Project Managers prior <br /> to discontinuing use of an extraction well . <br /> 3. The recommended monitoring program is presented on page 6-1 . Several <br /> considerations must be made prior to our approval . <br /> a. The recommended monitoring program includes testing for Aromatic (EPA <br /> Method 602) compounds on an annual basis with some exceptions. Underground <br /> storage tanks (USTs) wells would be tested on a semi-annual basis for EPA <br />