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kn KLEINFELDER • 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 iB-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 ' Monitoring wells are generally developed 24 to 48 hours after installation to allow the grout to set Each well is first sampled with a clear disposable bailer to visually inspect for a hydrocarbon layer or sheen If no product layer or sheen is observed on the water, the well is ' developed by surging, pumping or bailing Surging along the screened interval of the well is performed to draw the sediment from the formation into the filter pack and the well, and to set the sand pack Development continues until the discharge runs relatively clear of fines ' Approximately 5 to 10 well volumes are generally removed from each monitoring well Discharge water is stored in 55-gallon drums and left on site for later discharge or disposal by the client, depending on laboratory results The drums are labeled with the date, well number, and a contact person and phone number B-3 3 Equipment Decontamination To reduce the potential for cross-contamination between wells g equipment develo in e ment is washed P P in a tnsodium phosphate or non-phosphate detergent solution and rinsed in distilled water or steam cleaned pnor to use in the next monitoring well 28699 EOl I ST03R759 Page B-4 ' Copyright 2003,Klemfelder,Inc May 20,2003