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0 MEMORANDUM 0 <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A Phone: (916) 361-5600 <br /> Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 <br /> TO: Antonia K. J. Vorster FROM: Camilla Williams <br /> Senior WRC Engineer Engineering Geologist <br /> DATE: 26 June 1992 SIGNATURE: ILG�sLl�l/.Gt��e�i�/YyLl� <br /> SUBJECT: 1991 ANNUAL PROGRESS REPORT, DEFENSE D15TRIBUTION REGION WEST (DORW), <br /> SHARPE, SAN JOAQUIN COUNTY <br /> I have reviewed the 1991 Annual Progress Report submitted on 1 April 1992 for DDRW, <br /> Sharpe. On 20 May 1992, in a telephone conversation with Mr. Craig MacPhee of the <br /> U. S. Army Toxic and Hazardous Materials Agency (USATHAMA) , I discussed some of my <br /> major comments on the document. However, due to my scheduled absence (vacation) , I <br /> was unable to complete my written review of the Annual Report. We have memorialized <br /> our comments so that Sharpe will consider our concerns prior to implementing any <br /> changes in the monitoring program. Our major concerns with the Annual Report are <br /> discussed below. <br /> 1 . The Annual Report recommends sampling frequencies for monitor wells. Changes <br /> from the current monitoring frequency were not discussed. As is common in most <br /> of the technical reports submitted for Sharpe, the rationale supporting the <br /> proposed changes were not presented in the Annual Report. An open discussion on <br /> the changes in the monitoring frequency at the next Project Manager's Meeting <br /> may be the best forum for Sharpe and/or USATHAMA to present the rationale for <br /> the proposed changes. <br /> 2. The Annual Report indicates that A-4 and NA-7 are to be continued being used as <br /> extraction wells. Use of these wells should be discontinued because the <br /> contaminant concentrations are not high enough to support their use for <br /> extraction. The First Quarter 1992 data showed that the trichloroethylene (TCE) <br /> concentration in ground water in the area of A-4 was 1.02 micrograms per liter <br /> (µg/1 ) (2.67 µg/1 for total volatile organic constituents (VOCs)) and was 0.9 Ag/l <br /> (1 .07 Ag/l for total VOCs) in the area of NA-7. The continued use of these <br /> extraction wells may only serve to exacerbate the plume extent by pulling <br /> contaminants into unpolluted areas. In addition, if the aquifer cleanup level <br /> for TCE is to be 5 µg/1 , the Primary Maximum Contaminant Level (MCL) , as <br /> proposed in the ROD, then it is unclear why extraction wells would be needed in <br /> areas below the MCL. Unless the concentrations increase above the Primary MCL, <br /> these wells should not be used for extraction. <br /> 3. The recommended changes to the monitoring program are presented on page 4-1 . <br /> Several considerations must be made prior to our approval . <br /> a. Annual monitoring for aromatic VOCs (Method 602) is not acceptable for all <br /> areas of the site. Because the ground water is known to be contaminated <br /> with benzene, toluene, xylene and ethylbenzene (BTXEs) and because the fuel <br /> underground storage tank (UST) investigation is incomplete, annual <br /> monitoring for aromatic VOCs is unacceptable. Quarterly monitoring of wells <br /> in the area of USTs is required until the lateral and vertical extent of <br /> ground water contamination from these tanks is defined. However, annual <br />