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1 , File No- 20-3937-01 h� KLEINFELDER September �, 1996 i usually terminated 1 to 2 feet into the aquitard. Effort is made not to screen across two aquifers. if confined aquifer conditions or high vadose zone contamination is encountered, the well screen is usually not set above the depth of first encountered ground water. Wells are usually not set in areas of suspected significant soil contamination. • The PVC pipe and end caps are steam cleaned prior to installation. The annular sOace between the screen and the wall of the boring is backfilled with the appropriate clean ]sone Star Industries 0130 or 2112 Monterey sand to ipl?i'oximately 2 feet above the top of the perforatcd sections. . Based on soil logs or a sieve test, modifications may be made regarding the size of sand to be used. Installation of the 0130 sand may require that the sand be tremmied, using clean water. In this event, a sample of the tremie water is collected, unless the source is known to be clean. • l A 3- to 5400t bentonite plug is placed above the sand pack to provide a seal agalllSt Surface water itlfiltratlon. { The renlainin'o amlular space is liiled to the surface with trenullied Ccnlellt/bentO11ItC grout to the surf ace. • The wells are secured in a locking stovepipe: The well heads may be enclosed in a cement utility box set (lush to the ground surface located in a traffic area. 13-3.2 Monitoring Well Development and SamplinV Y Hic wells are developed to reduce the effects of drilling on the formation and to increase the effective hydraulic radius ofthe well. Monitoring wells are generally developed 24 to 48 hours after installation to allow the grout to set. Each well is first 'sanipicd 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, pumpilg, 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 frons the well at a rate of between 0.75 to 10 gallons per minute (gpin) depending on recharge rate and casing size. Development continues until the discharge' runs relatively clear of fines. Approximately 5 to 10 well volumes are generally 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. 20-3937-011 MR960189 Page No. Q-d Copyright 1996, Kleinfelder, Inc. Ii