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i � • File No. 20-3978-O1.Wr6 KLEINFELDER February 24, 1997 • The wells are generally screened from 5 feet above to 20 feet below first ground water. The screen length is reduced if an aquitard with a minimum thickness of 5 feet is encountered. If an aquitard is encountered the well is 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 space between the screen and the wall of the boring is backfilled with the appropriate clean Lone Star Industries 0/30 or 2/12 Monterey sand to approximately 2 feet above the top of the perforated sections. Based on soil logs or a sieve test, modifications may be made regarding the size of sand to be used. Installation of the 0/30 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. • A 3- to 5-foot bentonite plug is placed above the sand pack to provide a seal against surface water infiltration. • The remaining annular space is filled to the surface with tremmied cement/bentonite grout to the surface. • The wells are secured in a locking stovepipe. The well heads may be enclosed in a cement utility box set flush to the ground surface located in a traffic area. A-3.2 Monitoring Well Development and Sampling The wells are developed to reduce the effects of drilling on the formation and to increase the effective hydraulic radius of the well. Monitoring 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 are generally removed from each monitoring well. Discharge water is stored in 55- 10-3978-01.WR61107RE074.doc Page No.A-4 0 199 7, Kleinfelder,Inc.