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• DDAacy OU 1 Pesticide Remit diation Groundwater Extraction Well Installation Wc rk Plan 4.4 Bentonite Seal 5.0 POST-WELL-INSTALLATION ACTIVITIES The extraction wells will be constructed with a bentonite seal placed above the filter pack to 5.1 Extraction Well Development protect the filter pack during grouting.The bentonite seal will consist of bentonite pellets or Each extraction well will be developed after well chips. Once the seal is in place,the interval will casing installation. Well development pr -- be hydrated for a minimum of 30 minutes, dures will follow those outlined in the DD.'C- before grouting occurs. Guidelines for the Sharpe/Tracy Comprehensive Field Work Ian installation of the bentonite seal are presented in (URS,2001). Each well will be bailed wit' a the DDJC-Sharpe/Tracy Comprehensive Field sand-pump bailer to remove fine sand insi a the Work Plan (URS, 2001). well casing; bailing will continue until fin - grained sediment removed from the well 4.5 Cement Grout decreases to less than an estimated volume of 1 ounce of sediment in one bailer load. The well A cement grout will be used to fill the annular will then be surged for at least 30 minutes 3r space above the hydrated bentonite seal.Cement until the amount of sediment entering the well grout will consist of Type 11 Portland cement decreases to an amount deemed acceptable to the with 3 pounds of powdered non-beneficiated field geologist.Well development data to lie bentonite and 7 gallons of water per 94-pound recorded will include field measurement of pH, sack of cement. The cement grout will be temperature, specific conductivity,turbidity mechanically mixed with a paddle-type mixer data,the total number of well volumes pur ed and then tremied in place. No accelerator will be from the well during development, and the added to the grout. Guidelines for the installa- average pumping rate during development To tion of the grout seal are presented in the DDJC- comply with regulatory standards for addressing Sharpe/Tracy Comprehensive Field Work Plan potential pesticide impacts, development water (URS,2001). will require treatment by carbon absorption and air stripping methods already in place at th site. 4.6 Wellheads Groundwater removed during developmen will be conveyed through a 2-inch diameter Extraction wells and well headworks will be discharge hose to a tank for temporary stot age to installed to match wells currently in use at allow settling of fine sands. The groundw er DDJC-Tracy. Well headworks will be contained will be transferred to TP 2 by pumping the water in a 5-foot by 5-foot concrete vault.Protective out of the holding tank and through a carbon guard posts will be placed at each corner of the adsorption vessel located near EW022A, vault. Details describing the wellhead construc- approximately 600 feet south of TP 2.The water tion are addressed in the DDJC-Tracy Site OU I will then be conveyed to TP 2 through the Pesticide Remedial Design 100%Submittal existing groundwater conveyance pipeline (URS, 2002). 5.2 Well Location Surveying 4.7 Investigation-Derived Waste Horizontal coordinates will be determined to the Investigation-derived waste(IDW) will be closest 1.0 foot and referenced to the State Plane managed in accordance with the procedures Coordinate System,Zone 3,North Annericin described in the DDJC-Sharpe/Tracy Compre- Datum of 1983. Ground surface and top-o hensive Field Work Plan(URS,2001)and the casing elevations will be obtained at the DDJC-Sharpe/Tracy Waste Management Plan extraction wells to the closest 0.1 foot and 0.01 (Radian International,2000). foot,respectively. These elevations will be referenced to the National Geodetic Vertical Datum of 1988. K:\02237\OU I_Pest-RemVnal\GW-EW-WrkPln.dm 7 June 2002