A Report of Water Pollution in the South Platte River Basin February 1953

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available during the low flow periods during which irrigation diversions may occur, is at least 10 times greater than the anticipated maximum daily volume of sewage, in which case a bacterial reduction of 90 percent may be acceptable. Provided, however, that where the time of passage from plant dis- charge to irrigation diversion is such as to permit the normal death rate of bacteria as evidenced by the die -away curve to provide equivalent bac- terial reduction, the requirement of (1) and (2) above ma.,)r be appropri- ately modified. The protection of water rights must also be considered in determin- ing pollution prevention measures needed. Pollution control and the doctrine of appropriated rights as applied in the States of Colorado, Nebraska, and Wyoming, are perfectly compatible. Sewage treatment is a measure of conservation which greatly increases the usefulness of water and thus in a sense actually increases its value. Whether or not treat- ment requirements can be reduced by increasing the amount of dilution water is a decision which must be made on the basis of economics and the availability of water. The benefits to be derived will determine the degree of treatment and the amount of water which can be allocated for sanitation purposes. Waste treatment measures are usually tailored to the needs of a community following the engineering evaluation of local sanitary problems. Municipal treatment plants are usually of two general types, one of which removes settleable material from the sewage under quies -, cent flow conditions and the other removes additional polluting material by biological means. Within these categories numerous com- binations or adaptations thereof can be used to meet variant conditions of waste from a community and requirements of the receiving stream, Industrial treatment processes vary widely, often within the same general type of industry. Changes in processes, by- products recovery, salvage, improved housekeeping, and comparable practices are often very effective measures of controlling industrial pollution. Control of industrial wastes may present an entirely different problem than that of municipal wastes, since the industrial wastes may contain toxic or otherwise objectionable substances not amenable to either sedimenta- tion or biological treatment. However, the objective of the control program remains the same -- protection of waters by reduction of objec- tionable substances to within tolerance levels compatible with water uses. The water pollution control programs in the South Platte Basin are based on these premises. Sewage and waste treatment processes cannot be controlled pre- cisely, but they can be regulated between rather well established limits. The effective removal of solids from domestic wastes by sedi- mentation is termed primary treatment and is generally considered to reduce Biochemical Oxygen Demand;, from 25 to 40 percent. The removal of Biochemical Oxygen Demand by biological methods is termed secondary `Biochemical. Oxygen Demand is the quantity of oxygen utilized by microorganisms under aerobic conditions while feeding on and stabiliz- ing organic materiels under specified conditions of time and temperature. 37