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VI-l SECTION VI WATER QUALITY This discussion provides a cursory overview of water quality considerations, and the reader is referred to other publications for greater detail (1)(2) (3)(7) (8) (9). I NTRODUCTI ON South Platte River water quality changes significantly in the study reach from Chatfield Reservoir to Brighton; such changes are attributable to point and nonpoint source pollution from the Denver Metropolitan area. From Chat- field Reservoir to approximately Bowles Avenue, South Platte River water quality is generally good. The river has moderate to high concentrations of dissolved oxygen, appropriate concentrations of nutrients, low concentra- tions of metals and other pollutants and maintains a good fishery and over- all aquatic habitat. Recreational potential on the South Platte River between Chatfield Reservoir and Bowles Avenue with respect to water qual ity is good. The purposes of thi s section are the fo 11 owi ng: (1) List stream classifications and water quality standardS adopted by the Colorado Water Qual ity Control Commission which apply to the South Platte River in the study reach. (2) Di scuss the characteri st ic s of important water quality parameters and 1 i fe forms in the study reach. (3) Discuss sources of pollution in the study reach. Contrast relative contributions of point versus nonpoint source pollution. Assess the impact of water pollution on the South Pl atte River. (4) Discuss impacts of flood control alternatives on water quality. STREAM CLASSIFICATIONS AND WATER QUALITY STANDARDS The Colorado Water Quality Control Commission has established classifica- tions and numeric standards for the South Platte River and associated tribu- taries. As shown in Table VI-I, the study reach from Chatfield Reservoir to Brighton encompasses three stream "segments" as defined by the Water Qual ity Control Commission. These stream segments are numbers 6, 14 and 15. For the purposes of the following discussion, Class 1 waters are those which are safe for continuous body contact (swimming), while Class 2 waters permit only incidental contact (kayaking). Segment 6 is classified as having or is expected to have Class 1 recreation, Class I-cold water aquatic life, and water supply and agricultural uses. Segment 6 consists of the river reach from Chatfield Reservoir to_ Bowles Avenue. Segment 14, from Bowles Avenue to the Burlington Ditch diversion, is categorized as having Class 2 recrea- tion, Class I-warm water aquatic life, and water supply and agricultural uses. Stream Segment 15, from the Burlington Ditch diversion to Brighton, is categorized as having Class 2 recreation, Class 2-warm water aquatic life and water supply and agricultural uses. Stream segment 6 is expected to maintain dissolved oxygen concentrations of 6 mg/l (7 mg/l during spawning season) and should have fecal coliform concentrations not exceeding 200 per 100 milliliters. Segments 14 and 15, by contrast, both have established dissolved oxygen standards of 5 mg/l and fecal coliform standards of 2,000 per 100 mill iliters. Other nLlTleric standards for inorganics and metals reflect the fact that the South Platte River is expected to have lesser water quality from stream segment 6 through segments 14 and 15. Below Bowles Avenue, and extending to Brighton, however, water qual ity degrades as dissolved oxygen concentrations decrease, while concentrations of nutrients, metals, fecal coliform, organic and inorganic pollutants, and other substances associ ated with stormwater runoff, 1 andfill 1 eachate and sewage effluent increase. Consequently, recreational potential of the river in the reach between Bowl es Aven ue and Bri ghton is red uced . ASSESSING THE STATUS OF WATER QUALITY BY: (1) MONITORING PARAMETERS, AND (2) SURVEYING FISH AND BENTHIC ORGANISMS Selected water quality parameters and a survey of life forms within the river provide an indication as to the health of the river. Consequently, the following discussion reports on surveys by the Denver Regional Council of Governments (3) and the Colorado State Health Department (1) regarding selected water quality parameters and fish life in the study reach.