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R■ KLEINFELDER A-3 GROUNDWATER WELL INSTALLATION A-3.1 Monitoring Well Construction Construction details for shallow Soil and Groundwater Investigation wells are as follows: • The well casing are 2- or 4-inch inside diameter, flush threaded joint, schedule 40 PVC pipe. • The wells are constructed in 6- or 8-inch diameter borings. • Well screen sections are perforated with 0.010- or 0.020-inch factory-cut slots. • The wells are generally screened from 5 feet above to 15 feet below first groundwater. The screen length is reduced if an aquitard with a minimum thickness of 5 feet is encountered. If an apparent 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 are encountered; the well screen is usually not set above the depth of first encountered groundwater. Wells are usually not set in areas of suspected significant soil contamination. • The PVC pipe and end caps are steam cleaned prior to installation. f • The annular space between the screen and the wall of the boring is backfilled with the appropriate clean 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 sand may require that the sand be tremmied, using clean water. • 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. • The remaining annular space is filled to the surface with cement/bentonite grout. • The wells are secured in an aboveground or underground 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 wells. 12255.CW l /ST02R980 Page A-4 Copyright 2002,Kleinfelder,Inc. December 18,2002