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k" KLEIN FELDER used Installation of the 0130 sand may require that the sand be tremmied, using clean water. In this event, a sample of the tremae water is collected, unless the source is thought to be clean o A 3- to 5-foot bentonite plug is placed above the sand pack to provide a seal against surface water infiltration and to reduce the potential for cement grout to infiltrate into the water o The remaining annular space is filled to the surface with tremmied cement/bentonite grout to the surface. o The wells are secured in an above- or below-ground locking stovepipe. The well heads may be enclosed in a water tight cement utility box set flush to the ground surface when located in a traffic area A-3 2 Monitoring Well Development The wells are developed to reduce the effects of drilling on the formation and to increase the effective hydraulic radius of the well. Monitonng wells are generally developed 24 to 48 hours after installation to allow the grout to set. Each well is first sampled with a clear acrylic bailer to visually inspect for hydrocarbon layer or sheen If no product layer or sheen is observed on the water, the well is developed by surging, pumping or bailing Surging along the screened interval of the well is performed to draw the sediment from the formation into the filter pack and the well, and to set the sand pack. The sediment laden water is purged from the well at a rate of between 0 75 to 10 gallons per minute (gpm) depending on recharge rate and casing size. Development continues until the discharge runs relatively clear of fines. Approximately 5 to 10 well volumes generally are removed from each monitoring well. Discharge water is stored in 55-gallon drums and left on site for later discharge or disposal by the client, depending on laboratory results. A-3 3 Equipment Decontamination To reduce the potential for cross-contamination between wells, developing equipment is washed in a trisodium phosphate solution and rinsed in distilled water or steam cleaned prior to use in the next monitoring well A-3.4 Well Survey (3 wells only) The locations of soil borings and monitoring wells, and the elevation of the top of the PVC casings is usually surveyed and tied into permanent markers, if readily available Survey accuracy is 0.1 foot for the "x" and "y" coordinates and 01 foot for the "z" coordinate. The depth to static ground water is measured from a set location at the top of the PVC casing The depth of water is then subtracted from the elevation of the top of the well casing to provide a ground water elevation for each monitoring well location. •