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or screen shall be watertight. Any perforations shall be below the depths specified in Section 9, Subsection A, page 14, above. Casing shall be equipped with centering guides or 'centralizers' to ensure the even radial thickness of the annular seal and filter pack. 1. Metallic Casing. Metallic casing may be joined by welds, threads, or threaded couplings. Welding shall be accomplished in accordance with the standards of the American Welding Society or the most recent revision of the.American Society of Mechanical Engineers Boiler Construction Code. Metallic casing shall be equipped with a 'drive shoe' at the lower end if it is driven into place. 2. Plastic Casing. Plastic casing may be joined by solvent welding or mechanically joined by threads or other means, depending on the type of material and its fabrication. Solvent cement used for solvent welding shall meet specifications for the type of plastic casing used. Solvent cement shall be applied in accordance with solvent and casing manufacturer instructions. Particular attention shall be given to instructions pertaining to required setting time for joints to develop strength. The following specifications for solvent cements and joints for PVC casing shall be met, including the latest revisions thereof: a. ASTM D2564, Standard Specification for Solvent Cements for Poly (Vinyl Chloride) (PVC) Plastic Pipe and Fittings. b. ASTM D2855, Standard Practice for Making Solvent-Cemented Joints with Poly (Vinyl Chloride) (PVC) Pipe and Fittings. Plastic casing or screen shall not be subjected to excessive stress during installation and shall not be driven into place. Care shall be taken to ensure that plastic casing and joints are not subjected to excessive heat from cement-based sealing material. A specifically designed adapter shall be used to join plastic casing to metallic casing or screen." Section 14. Well Development. Section 14 (page 46 of Bulletin 74-81) has been revised as follows: "Development, redevelopment,or reconditioning of a well shall be performed with care,by methods that will not damage the well structure or destroy natural barriers to the movement of poor quality water, pollutants, and contaminants. Acceptable well development, redevelopment, or reconditioning methods include: • Overpumping; • Surging or swabbing by use of'plungers'; • Surging with compressed air; • Backwashing or surging by alternately starting and stopping a • Jetting with water; -26-