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• i <br /> specified. Centralizers will not be attached to the well screen or that part of the well <br /> casing exposed to the gravel pack. All joints will be constructed to provide a straight, <br /> non-constricting, and watertight fit. Any casing or screen deformation or bending will be <br /> minimal to the point of allowing the insertion and retrieval of the pump and/or bailer <br /> optimally designed for that size casing. <br /> The contractor will provide means of protecting the well bore and casing assemblies, <br /> when installed, from the entrance of foreign objects. The entry of nuisance water, such as <br /> rainfall runoff or construction water from other construction activities, into the borehole <br /> will be prevented. The contractor will protect the work from damage and take all <br /> measures necessary to prevent delays. <br /> 2. Filter Pack, Bentonite Seal, and Grout <br /> Well backfill materials (e.g., filter pack, bentonite, and grout) will form a continuous <br /> annular filling around the well casing. The filter pack will be sand composed of sound <br /> durable particles and will be free of organic matter, clay balls, and other deleterious <br /> substances. Sand material used in the pack around the well screen will be selected to be <br /> compatible with both the screen slot size and aquifer materials. Based on the 0.020-inch <br /> slot well screen,the anticipated filter pack size will be equivalent to 10 x 20 Colorado <br /> Silica Sand or RMI No. 3 sand. The filter pack size may be modified based on the results <br /> of the formation sample sieve analysis. The pack will have a uniformity coefficient less <br /> than 2.5. The pack will be properly cleaned and bagged by the supplier. The filter pack <br /> will be installed a minimum of 6 inches below the screen, and from 2 to 5 feet above the <br /> screen. <br /> A 5-foot bentonite seal will be placed on top of the pack material. The bentonite seal will <br /> be composed of high quality bentonite pellets, as manufactured by Volclay or equal. <br /> Unchlorinated water will be added to ensure that the pellets expand to form a tight seal. <br /> Properly wetted bentonite pellets are the most time-effective form of bentonite for this <br /> application. <br /> A bentonite-cement grout seal will extend from the top of the bentonite seal to the land <br /> surface. Bentonite powder will be mixed with water before the cement is added to the <br /> mix. Grout may be mixed at the well site by the contractor, or purchased from a ready <br /> mix supplier, provided that the supplier can provide current water quality analyses <br /> showing the mix water to be free from VOC, chlorine, inorganics, or other sources of <br /> contamination. The grout will be pumped into the annular space under pressure using a <br /> tremie pipe placed at the top of the bentonite seal to ensure a continuous grout seal. The <br /> protective casing will be set in the grout. Grout will be left undisturbed for 24 hours after <br /> placement. After the grout seal has set, it will be checked for settlement, and additional <br /> grout of approved composition will be added to fill any depressions. <br /> Grout will be composed by weight of 20 parts Portland cement to 1 part bentonite, with a <br /> maximum of 10 gal of approved water per 94 lb bag of cement. Bentonite powder used <br /> in the seal will be a commercially available product designed for well sealing. Overall, <br /> Project Workplan 4 SA1433 <br /> July 30,2004 n:\sa01433\gwmwiwp\workplan.doc <br />