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ddMIL KLEINFELDER B-3 GROUNDWATER WELL INSTALLATION B-3.1 Monitoring Well Construction Construction details for shallow groundwater monitoring wells are as follows: • The monitoring wells will have casings consisting of 2 -inch inside diameter, flush - threaded joint, Schedule 40 PVC pipe. These wells will be constructed in 8 -inch diameter borings. • Well screen sections will be perforated with 0.010- or 0.020 -inch factory -cut slots. The perforation sieve openings are assessed (and modified if required) after the borings are logged, and if warranted, a sieve test has been performed and the results received. • The wells will be generally screened from 30 feet to 55 feet below subgrade. 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 is encountered, the well screen in 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 will be 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 thought to be clean. • A 3- to 5 -foot bentonite plug is placed above the sand pack to provide an annular 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 tremmied cement/bentonite grout (surface seal) to the surface. • The wells will be secured in a below -ground locking stovepipe and the well heads enclosed in a water -tight cement utility box set flush to the ground surface. 20-3978-0I.W36/2017P 117 Page B-3 © 1997, Kleinfelder, Inc. September 5, 1997