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• MEMORANDUM A CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION Sacramento, 3443 toRoad, Suite Phone: (916) 255-3000 , CA 95827-30998 CALNET: 8-494.3000 TO: Antonia K. J. Vorster � FROM: James Taylor Senior WRC Engineer Associate Engineering Geologist DATE: 11 June 1993 SIGNATURE: SUBJECT: STATEMENT OF WORK (SOW) FOR GROUNDWATER TREATMENT REMEDIAL DESIGN AND WELL INSTALLATION IN SUPPORT OF REMEDIAL DESIGN, OPERABLE UNIT N0. I (OU-1), DEFENSE DISTRIBUTION REGION WEST (DDRW), TRACY, SAN JOAQUIN COUNTY I have reviewed the SOW for the Groundwater Treatment Remedial Design. and Well Installation in Support of Remedial Design for OU-1 at DDRW, Tracy submitted on 13 May 1993. Overall the SOWs contain the basic elements needed to proceed with the Remedial Design. My comments on the above referenced submittals are discussed below. Statement of Work - Groundwater Treatment Remedial Design 1 . Page A-2, Section 3. 1; This section states that Waste Discharge Requirements (WDRs) will be established in the Record of Decision (ROD) . The WDRs are not established in the ROD. Effluent limits that will be proposed for adoption in the WDRs will be reflected in the ROD. The actual WDRs will be adopted by the Regional Board probably after the ROD has been approved. This section must be revised accordingly. 2. Page A-6, Section 3.3.2; See comment No. 1 above. 3. Page A-6, Section 3.3.3; This section states that an extraction well network is being installed by the Government at this time for the proposed central area plants; the AE shall incorporate the extraction wells installed by the Government into this design. This statement is incorrect. The current IRM system includes percolation/evaporation ponds, and an extraction and injection well network. The AE must incorporate the current IRM system into the Remedial Design Documents. 4. Page A-15; The zip code for the RWQCB is incorrect. The correct address is on this cover letter and memorandum headers. 5. Page A-22, Section 7.3.3.2.2; This section states that the well screen shall be twenty (20) feet in length for monitoring wells, forty (40) feet in length for withdrawal wells and sixty (60) feet in length for injection wells unless otherwise approved. These specifications are acceptable for estimating costs and for scoping purposes only. Actual construction specifications should be based on existing data and data collected from pilot boring E-logs and drilling logs prior to well construction. Well screen intervals should correspond to the targeted aquifer zone's most permeable layers. Monitoring wells and extraction wells screened across fine grained material are apt to yield turbid samples or convey excessive silt to the treatment and disposal facilities. Monitoring wells installed in the lower horizons may be installed with screen lengths of 10 feet or greater in order to remain consistent with the existing monitoring wells.