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LK E/NFELDER enemvoyie xgnsowaon. The wells will be constructed in 8-inch diameter boreholes. ' a Well screen sections are perforated with 0.010- or .020-inch factory-cut slots. t This parameter is assessed (and modified if required) after the boring logs and, if warranted, a sieve test has been performed and the results received. The wells are generally screened from 5 feet above to 20 feet below first groundwater. 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. t . 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. ' 101486.4/STO12R025 Page A-4 February 1, 2012 Copyright 2012 Kleinfelder