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MEMORANDUM <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: Robert Evans <br /> Senior Engineer Area Engineer <br /> DATE: 17 May 1990 SIGNATURE: <br /> SUBJECT: REVIEW OF REVISED WORKPLAN FOR HYDROGEOLOGIC CHARACTERIZATION REPORT <br /> Tri Valley Growers (TVG) Plant No. 4 submitted a Revised Workplan for a hydrogeologic <br /> assessment as required by waste discharge requirements Order No. 88-147. Since TVG <br /> discharges up to 4.0 million gallons per day (mgd) by flood irrigation over an area of <br /> approximately 350 acres, a hydrogeologic assessment was required to delineate the <br /> geology underlying the site and assess the potential impacts on ground water quality <br /> due to land disposal . In addition to the hydrologic assessment, TVG is required to <br /> characterize the site lithology and determine the percolation rates in the unsaturated <br /> zone. <br /> Prior to the borings being completed as monitoring wells, soil samples will be taken <br /> every 5 feet using a 2.5 inch ID split spoon sampler containing three brass tubes. We <br /> request that TVG take continuous soil core samples in the first borehole and soil <br /> samples every 5 feet in the other 4 soil borings. The soil samples and drill cuttings <br /> will be used to log each well by an experienced field geologist or civil engineer using <br /> the Unified Soil Classification System. The well logs will be included in the final <br /> report. <br /> Three falling head infiltrometer tests will be conducted across the site to determine <br /> percolation rates. The percolation rates will be integrated with borehole sample data <br /> to consider flow paths in the vadose zone and the potential for the development of <br /> perched zones. <br /> TVG will install five borings/monitoring wells (see attached map) to meet the <br /> following objectives: <br /> 1 . Determination of the hydraulic gradient. <br /> 2. Establishment of seasonal/temporal changes in ground water conditions. <br /> 3. Estimation of recharge and ground water flow rates. <br /> 4. Characterization of ground water quality over time. <br /> 5. Site geology and definition of first aquifer. <br /> The Workplan states that each monitoring well will be constructed with 2 inch PVC <br /> casing screened 5 feet above and 15 feet below the encountered water table to allow for <br /> seasonal water level fluctuations. However, the screen should be placed based on the <br /> lithology encountered and the location of the first permeable zone. The screen slot <br /> size will be 0.01 inch. <br />