Seepage from rivers and irrigation canals has contributed to waterlogging and soil salinization problems in much of the Indus Plains of West Pakistan. These problems are being overcome in part by tube-well dewatering and deep leaching of salinized soils. The ground waters described here are anaerobic and some are supersaturated with troublesome minerals such as calcium carbonate (calcite) and iron carbonate (siderite). These waters are moderately corrosive to steel. Some wells contain sulfate-reducing bacteria, which catalyze corrosion, and pH-electrode potential relationships favorable to the solution of iron also are rather common. Corrosion is concentrated in the relatively active (anodic) saw slots of water-well filter pipes (screens), where metal loss is least tolerable. Local changes in chemical properties of the water, because of corrosion, apparently cause deposition of calcium carbonate, iron carbonate, and other minerals which clog the filter pipes. In some places well capacities are seriously reduced in very short periods of time. There appears to be no practicable preventive treatment for corrosion and encrustation in these wells. Even chemical sterilization for bacterial control has yielded poor results. Periodic rehabilitation by down-hole blasting or by other effective mechanical or chemical cleaning methods will prolong well life. It may be possible to repair severely damaged well screens by inserting perforated sleeves of plastic or other inert material.
The most promising approach to future, well-field development is to use filter pipes of epoxy-resin-bonded fiber glass, stainless steel, or other inert material which minimizes both corrosion and corrosion-catalyzed encrustation. Fiberglass plastic pipe appears to be the most economically practicable construction material at this time and already is being used with promising results.