SITE INFORMATION AND CORRESPONDENCE_1988-1991

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. MEMORANDUM • CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: ( 16) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: Antonia K. J. Vorster j�q,/ FROM: Camilla Williams Senior WRC Engineer Engineering Geologist DATE: 13 March 1991 SIGNATURE: CGG�(/`�tllit�ll SUBJECT: REVIEW OF FOCUSED FEASIBILITY STUDY, PRELIMINARY DRAFT, DEFENSE DISTRIBUTION REGION WEST (ODRW), SNARPE SITE, SAN JOAQUIN COUNTY I have reviewed the Focused Feasibility Study (FS) for the Central Area at the DDRW, Sharpe Site. Overall , the FS is quite comprehensive with respect to treatment technologies. The purpose of this FS is to focus on the remediation of the contaminated ground water which consists of pump, treat and disposal phases. The FS proposes to pump and treat ground water for all of the remedial scenarios and compares five ground water treatment technology alternatives for the Central Area . These alternatives included air stripping, granular activated carbon (GAC) , ozonation with hydrogen peroxide (H202) and ultra violet (UV) light, fixed-bed biological reactors and no action. The recommended remedial treatment alternative for the Central A ea is air stripping. The FS also evaluates two disposal methods. Below I have provided discussions on the major topics which should be consi ered for the revision of future drafts of the FS prior to our concurrence with the selected remedial measure. EXTRACTION WELLS I have several concerns with the proposals for the extraction wells. My major concern is that the FS did not present the proposed construction diagrams for the a traction wells, therefore the vertical coverage of these wells is unknown. The FS hould be revised to contain the proposals for the extraction well design including screen length and slot size, screen and casing materials and diameter, annular seal materials, filter pack and the rationale for the particular design. Fifteen proposed extraction wells have been located using the Random Walk mo el . The number and location of the proposed extraction wells do not always appear t be well justified and should be reconsidered. Based on my review of the proposed 1 cations, it appears that the number of extraction wells may be reduced depending on t e design of the well and that the extraction well locations should be relocated to correspond with the areas of highest trichloroethene (TCE) contamination. The proposed pumping scheme of the extraction wells does not appear to be optimal and should be revised. In the proposed pumping scheme, the extraction wells in the A, B and C zones are pumping at rates which remain constant throughout the year. The Remedial Investigation (RI) Report indicated that pumpage from nearby agricultural -V1 d jj gra i JJ appaw 1 �u oo 1411 d ueu�niy N i U le ulUVC111Cn L. nuwever, Lae propose pumping scheme does not vary to account for changes in agricultural pumpage which is known to occur on a seasonal basis. The proposed pumping scheme may not be as effective as =nticiDated if it is not adjusted to account `or the seasonal influences of agricuitural pumpage.