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��®Qeraca-o,aort performed) and will select the well materials and techniques for well completion to be compatible with the subsurface conditions and the intended use of the well. Construction of all wells will be in conformance with the following provisions. A TYPICAL MONITORING WELL CONSTRUCTION DIAGRAM is attached. 2.1 WELL SCREEN AND CASING The well casing will generally consist of threaded stainless steel or schedule 40 (minimum) polyvinyl chloride (PVC) casing. The inside diameter of the casing will be large enough to permit easy passage of an appropriate water-level probe and equipment for purging wells and water sample collection. The well screen will generally consist of machine-slotted PVC or wire-wrapped stainless steel screen. The slot sizes will be compatible with the selected filter material. The screened sections will provide flow between the target zone and the well, allowing efficiency in well development and collection of representative samples. 2.2 FILTER MATERIAL Filter material will be well-graded, clean sand (generally less than 2 percent by weight passing a No. 200 sieve and less than 5 percent by weight of calcareous material). The filter material will be either a standard sand gradation designed for a range of anticipated soil types or a sand gradation specifically designed to fit the soils collected from anticipated well completion zone. 2.3 SETTING SCREENS AND RISER CASING Upon completion of drilling and/or geophysical logging, the boring will be sounded to verify the total depth, and the well casing will be assembled and lowered into the boring. Well casing materials will be measured to the nearest 0.1 foot and steam-cleaned before being lowered into the borehole. The well assembly will be designed so that the well screen is opposite the target zone. The bottom of the well will be fitted with a secure bottom-end cap. No PVC cement or other solvents will be used to fasten the well casing joints, well screen joints, or end caps. When installing wells in an open borehole, stainless steel centralizers will INSTALLATION AND DESTRUCTION OF WELLS Page 2 of 8 MSCIPROTO-IW.T,T REVISION DATE:MARCH 1996 IW-2