FIELD DOCUMENTS AND WORK PLANS 1992-1999

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• MEMORANDUM • CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 J ATSS Phone: 8-495-5600 TO: Antonia K. J. Vorster� ((i�1/ FROM: Camilla Williams Senior WRC Engineer Engineering Geologist DATE: 10 December 1991 SIGNATURE: SUBJECT: REVIEW OF GROUNDWATER INJECTION FEASIBILITY STUDY, MARLEY COOLING TOWER COMPANY, SAN JOAQUIN COUNTY I have reviewed the Groundwater Injection Feasibility Study (FS) submitted on 9 September 1991 by Hargis and Associates (Hargis) for the Marley Cooling Tower Company (Marley) . The Injection FS evaluated the treatment effluent compatibility with ground water. Four mixtures were evaluated: a 50/50 mix of the ion exchange treatment effluent combined with the electrochemical treatment effluent; a 50/50 mix of the ion exchange treatment effluent combined with ground water; a 50/50 mix of the electrochemical treatment effluent combined with ground water; and a 25/25/50 mix of the ion exchange and electrochemical treatment effluents combined with ground water. In addition, two different injection intervals were evaluated for the latter three mixtures. The evaluated injection intervals are Interval A at 200 to 245 feet below ground surface (bgs) and Interval B at 200 to 400 feet bgs. The Injection FS also evaluates the impacts on the remedial wellfield design using injection wells at two different locations: on the North Yard and adjacent to the Stockton Diverting Canal . Both well locations were evaluated using the January 1987 and July 1991 flow conditions. The FS Report concludes that precipitation due to chemical incompatibility is not expected for the majority of the evaluated mixing scenarios, except for the worst-case mixing scenario in Interval A. The FS Report also concludes that injection wells at the Stockton Diverting Canal would produce minimal adverse impacts on the remedial wellfield. The FS Report recommends that bench scale testing be performed to confirm the potential for precipitation, recommends a deep target injection zone and generally indicates that injection is a feasible alternative for the disposal of the treated ground water effluent. Overall , the Injection FS Report is well prepared and documented. Hargis has submitted excellent summary tables and graphics which helped in the review of the Report. However, my major concern with the Injection FS is that only two locations and one pumping rate for the injection wells were considered. In addition, the potential for the formation of precipitate with the "recipient" ground water between the two different injection well locations (the North Yard and adjacent to the Stockton Diverting Canal ) was not considered. These two injection well locations differ in that one location is in an area impacted by the plume (North Yard) while the other location (Stockton Diverting Canal ) is not. Because the concentrations of general minerals may be higher in areas of the aquifer that have been contaminated, it may be possible that the ground water beneath the North Yard has the potential for the formation of precipitate. In addition, with a limitation on well placement, it is not possible to evaluate the use of injection wells as a hydraulic control of the plume and to aid plume capture. The FS considered only two injection wells at a combined rate of 500 gallons per minute