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' • �� KLEINFELDER B-3 GROUNDWATER WELL INSTALLATION ' B-3.1 Monitorine 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. ' 0 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. ' 20-4341-11.E01/201IR959 Page B-4 Copyright 2001,Mcinfelder,Inc. August 21,2001