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I D. Pump Blowoff. When there is a blowoff or Section 12. Casing. drain line from the pump discharge, it shall be located 111 above any known flood levels and protected against the A. Casio Material. Requirements pertaining to possibility of backsiphonage or backpressure. The blowoff well casing are to insure that the casing will perform the or drain line shall not be connected to any sewer or storm functions for which it is designed, i.e., to maintain the drain except when connected through an air gap. hole by preventing its walls from collapsing, to provide a channel for the conveyance of the water, and to provide a E. Air Vents. In community water supply wells to measure of protection for the quality of the water pumped. minimize the possibility of contamination caused by the creation of a partial vacuum during pumping, a casing vent 1. Well casing shall be strong and tough shall be installed (Figure 7). In addition, to release air enough to resist the forces imposed on it during installation trapped in the pump column when the pump is not running, air and those forces which can normally be expected after release vents shall be installed (Figure 7). Air vents are installation. also recommended for other types of wells except those having jet pump installations requiring positive pressure (which 2. Steel is the material most frequently used cannot have a vent). for well casing., especially in drilled wells. The thickness of steel used for well casing shall be selected in accordance F. Backflow Prevention. All pump discharge with good design practices applied with due consideration to pipes not discharging to the atmosphere shall be equipped conditions at the site of the well. There are three with a check valve or similar device to prevent backflow and/ principal classifications of steel materials used for water or backsiphonage into the well when the pump shuts down. The well casing, and all are acceptable for use so long as they check valve shall be installed between the pump head and the meet the following conditions. connection to the distribution system or standpipe. Section 11. Disinfection and Other Sanitary Requirements. Abbreviations used are: API-American Petroleum Institute; A: Disinfection. All wells producing water for ASTM-American Society for Testing and Materials; AWWA- domestic use (i.e., drinking or food processing) shall be American Water Works Association. disinfected following construction, repair, or when work is 2f Selection of casing depends on its ability to resist done on the pump, before the well is placed in service. external forces as well as factors affecting the casing serviceability. The maximum theoretical external pressure B. Gravel. Gravel used in gravel-packed wells under which a particular well casing of a specific shall come from clean sources and should be thoroughly washed diameter and thickness will collapse can be calculated. before being placed in the well. Gravel purchased from a However, other .considerations such as the effect of supplier should be washed at the pit or plant prior to driving the casing into place or other impact forces which delivery to the well site. may have an effect on the ability of a particular casing to resist external pressures, cannot be calculated with During placement of the gravel in the annular space accuracy. Good design practices preclude the selection of disinfectants (usually calcium hypochlorite in tablet or a casing of a particular thickness for use where it will granular form) shall be added to the gravel at a uniform experience external pressures approaching the maximum or rate (two tablets per cubic foot or one pound of the granular where unknown forces might magnify the effect of the form per cubic yard). external forces. Instead it is customary for designers to introduce factors of safety which tend to ensure that the C. Lubricants. Mud and water used as a drilling casing selected will resist all probable forces imposed lubricant shall be free from sewage contamination. Oil and upon it. Consequently, experience and sound judgment, water used for lubrication of the pump and pump bearing shall coupled with these factors or safety, have so far proved also be free from contamination. to be the best guide in se:lectmg the proper casing. Suggested thicknesses for steel casing for various depths and diameters are to be found in material published by the various steel manufacturers and fabricators and in publi- The potential for the accidental contamination of wells cations on the design of. water wells. The suggested through backflow or backsiphonage is high, particularly thicknesses contained in such publications are not to be where there is the possibility of interconnection with considered a part of these standards. other systems or in systems where agricultural chemicals (fertilizers, pesticides, etc.) are being injected. 1 A procedure for disinfecting a well is described in Appendix C.