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. . . <::::l ca l'~. o OTHER WATER QUALITY ASPECTS (Continued) 3. Agricultural Wastes Except for salinity, pesticides and fertilizers are the primary water pollutants associated with agriculture in the Colorado River Basin. Here again the Environmental Protection Agency and States have been endeavoring to control the discharge of these pollutants into the wateI'YIays. (Discharges from irrigated agriculture return flows, how- ever, do not require a section 402 NPDES permit nor does a discharge or dredge or fill material from normal farming require a section 404, PL 92-500, Army Corps of Engineers Permit.) The chlorinated hydrocarbon group, e.g., DOT and Toxaphene, are the most persistent pesticides and are of primary concern because of their long-range impact. Efforts are being made, however, to control use of these types of pesticides. The organic phospbate compounds do not persist in the environment for the period the chlorinated hydrocarbons do, but they are more toxic to fish and humans. Nitrogen and phosphorus fertilizers are the most commonly used in the basin. Studies conducted in other areas of the United States show a relationship between the concentrations of nutrients from agricultural lands and water quality problems caused by excessive fertiliziation of aquatic plants. Within the Colorado River Basin the animal waste pol- lution is minimal because outside surface water has been prevented from entering tbe feedlots either by directing the drainage away from the operation or by locating the facility in a favorable topographic posi- tion. Additional discussion of toxic materials and nutrients are pre- sented later in sections 5 and 6 Part IX. 4. Mine Drainage During the period 1966 to 1968 approximately 75 locations were sampled to determine the heavy-metal concentrations contributed by mine drainages, tailing piles, and natural sources within the Colorado River Basin. Since that time the States and the Environmental Protection Agency have been endeavoring to control the pollution from these sources. B. Water Quality Parameters Other Than Salinity Detailed obtained from the Co lorado Part X. information concerning the following parameters can be results of special studies made in the various reaches of River Basin. Some of these studies are mentioned in 1. Dissolved Oxygen The dissolved-oxygen concentration is a measure of capacity to support life and assimilate organic wastes. the water The records 101