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<br />VI-3 <br /> <br />majority of the time on most of the river. The iron standards for aquatic <br />life are routinely violated below 8th Avenue. All of the other metals men- <br />tioned above have been detected during sampling programs, although of these <br />remaining metals, only zinc exceeded standard~ in Table VI-I. <br /> <br />Company of Colorado Cherokee Power Plant discharge site. The percent that <br />each fish species represented of the total catch at each station is pre- <br />sented in Table VI-3 (3). <br /> <br />Organic Matter. Mean concentrations of biochemical oxygen demand (BOD) are <br />low. For example, upstream from the Denver Metro plant, BOD concentrations <br />do not exceed 13 mg/l. Chemical oxygen demand values are also considered <br />relatively low. Val ues for both bOD and chemical oxygen demand (COD) show <br />tangible increases below the Denver Metro plant and elevated BOD and CDD <br />level s are expected to remain through Brighton. <br /> <br />As depicted in Figure VI-I, low densities of fish were found in sites having <br />predominantly sandy substrate. Only 0.098 fish per foot were captured at <br />the Cooley/Crawley gravel site where the river bottom was sand overl aid on <br />cobbles. The greatest density was found at Confluence Park, a diverse sec- <br />tion including pebbles, cobbles, a ditch diversion dam and a recreational <br />kayak chute which provides some aeration to the water. A pool exists down- <br />stream of the diversion dam (3). <br /> <br />Salt. Mean sodium concentrations range from approximately 70 mg/l in the <br />winter to 6D mg/l in the SlJnmer, while chloride concentrations are approxi- <br />mately 60 mg/l and 50 mg/l, respectively. The highest mean chloride concen- <br />trations recorded are 100 to 150 mg/l for winter months. These values can <br />be compared with the most stringent use criteria which is 250 mg/l for chlo- <br />ride in water classified for water supply (1). <br /> <br />While the South Platte River, as a high plains stream, naturally contains <br />much unstable shifting substrate creating poor fish habitat, the condition <br />may be exacerbated by additional input sediment from runoff(3). <br /> <br />Fish Fauna. A total of 17 species were collected in the South Platte River <br />from the upstream site near the Highway C-470 bridge to the Public Service <br /> <br />Benthic Organisms. The results of the benthic stream-reach survey indicate <br />that benthic organisms are principally controlled by settled solids loading <br />in the South Platte River. Clean water macroinvertebrates inciuding May <br />flies, caddis flies, and black fly larva were found at sights downstream of <br />Chatfield Dam to Oxford Avenue. Pollution-tolerant organisms were only 8 <br />percent of the total community below Chatfield Dam, but comprised 96 percent <br />of the macroinvertebrates below the Littleton/Englewood wastewater treatment <br />plant at the Florida Avenue site. The density of sludge worms at this site <br />was quite high at 1,488 per square foot. Downstream of Florida Avenue, the <br />dominant groups found were sludge worms, blood worms and nematodes. Below <br />the Denver Metro wastewater discharge at the site above Clear Creek, sludge <br />worms constituted 99 percent of the fauna and occurred in densities of <br />nearly 1,000 per square foot on cobble and approximately 2,000 per square <br />foot on gravel. Significant improvements in the fauna were not evident <br />downstream at 123rd Avenue, Henderson, Colorado(3). No recorded sampling of <br />benthic organisms is available between 123rd Avenue and Brighton, although <br />little improvement is expected. <br /> <br />Aquatic Life in the South Platte River <br />The Denver Regional Council of Governments (DRCOG) in its recent study <br />entitled "Urban Runoff Quality in the Denver Kegion" (3) describes a quali- <br />tative survey of fish and benthic organisms which was conducted in the South <br />Platte River below Chatfield Dam to Henderson, Colorado in an effort to <br />assess the effect of urban runoff on aquatic biota. DRCOG was assisted by <br />the Environmental Protection Agency and Colorado Division of Wildl ife in <br />this endeavor. DRCDG focused its investigation on the fish fauna and ben- <br />thic organisms by sampl ing at the 13 locations indicated in Table VI-2. <br />Fish were collected within 200 foot stretches of river at each sampling <br />location by electroshocking and were identified, counted and weighed. Much <br />of the following text is excerpted directly from this DRCOG report. <br />