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File No. 20-3978-01.W 16 JU KLEINFELDER January 8, 1997 B-3 GROUNDWATER WELL INSTALLATION B-3.1 Monitoring Well Construction Construction details for shallow groundwater monitoring 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 8- or 10-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. • 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. 20-3978-O1.W161207PE014 Page 6-4 Copyright 1997, Kleinfelder,Inc.