Complete Retention Ponds

In areas of the world where the moisture deficit (evaporation minus rainfall) exceeds 30 in. (75 cm) annually, a complete retention wastewater pond may prove to be the most economical method of disposal if low-cost land is available. The pond must be sized to provide the necessary surface area to evaporate the total annual wastewater volume plus the precipitation that would fall on the pond. The system should be designed for the maximum wet year and minimum evaporation year of record if overflow is not permissible under any circumstance. Less stringent design standards may be appropriate in situations where occasional overflow is acceptable or an alternative disposal area is available under emergency conditions. Monthly evaporation and precipitation rates must be known in order to size the system properly. Complete retention ponds usually require large land areas, and these areas are not productive once they have been committed to this type of system. Land for this system must be naturally flat or must be shaped to provide ponds that are uniform in depth and have large surface areas. The design procedure for a complete retention wastewater pond system is relatively detailed; the procedure can be obtained from the National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161 (ask for the EPA-625/1-83-015 document).

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