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VI-6 to the South Platte River; consequently, no discussion regarding ~I.__- ~_..:_.. l.!Ie:::.e !-'U 1111.. South Adams County Sewage Treatment Plant The South .Ad ams County Sewage Treatment Pl ant d i schilrgf's approx imately 2.2 to 2.6 MGD of sewage which has been treated via either trickling filters or rotating biological contact units. The plant operates under a discharge permit of 3D mg/l BOD and 30 mg/l suspended solids. No iiTlmonia or phosphor- us permit limitations exist. The South Adams County plant typically dis- charges 16 to 17 mg/l of ammonia while phosphorous levels are not measured. nor Public Service Company contributed significant quantities of pollution sources of pollution is provided. The following information was derived from a series of interviews with sewage treatment plant operators(4){5){6). Littleton/Englewood Sewage Treatment Plant The Littleton/Englewood Sewage Treatment Plant has a discharge permit for up to 28 million gallons per day (MGD); however, typical flows currently are 15 to 17 MGD. The Littleton/Englewood plant actually consists of two treat- ment plants, but both plants operate under one discharge permit. The plants consist of activated sludge and operate under a BOD discharge permit of 20 mg/l and a suspended solids limitation of 20 mg/l. No discharge limitations currently exist for either ammonia or phosphorus. Concern over ammonia loading in the South Platte River in the vicinity of Englewood and Littleton prompted these cities along with the Colorado State Health Department to hire the U.S. Geological Survey to undertake a comprehensive water quality study of the South Platte in the reach from Chatfield Reservoir to 50th Ave- nue. The results of this ongoing study should be available in final form late in January 1985(2). Leachate From Solid Waste Landfills Sol id waste disposal site leachate may adversely affect the South Pl aUe River in a number of locations, beginning near Oxford Avenue, although this supposition requires field verification. Denver Metropolitan Wastewater Treatment Plant The Denver Metro plant operates under permit limitations of 20 mg/l for BOD and 20 mg/l for suspended solids. The plant generally meets these criteria. No treatment currently exists for ammonia, and discharge concentrations of this substance typically range from 17 to 18 mg/l. Total phosphorus concen- trations in Denver Metro discharges are approximately 2 to 8 mg/l, and no limitation exists for phosphorous. The Denver Metro plant consists of con- ventional activated sludge and pure oxygen activated sludge processes. Average annual flows for the plant are approximately 145 MGD. Denver Metro receives sewage which has received primary treatment from the old Denver Northside plant. Eventually, however, primary treatment capability of Denver Metro will be enlarged to such an extent that it will no longer be COMPARING PDLLUTANT LOADS FROM POINT VS. NON-POINT SOURCES OF POLLUTION Table VI-II provides estimated point source base flow and storm runoff loads for April 1980 through September 1981 for the South Platte River at 50th Avenue and provides point source base flow and storm runoff loads expressed as a percentage of total basin loads for the same timespan at 5Dth Avenue. Both of these tables have as their basis the September 1983 DRCOG report entitled "Urban Runoff Quality in the Denver Region". The data presented in these tables are based on three six month periods: (1) April 1980 through September 1980, (2) October 1980 to March 1981, and (3) April 1981 through September 1981. The point sources (major point sources above 50th Avenue included wastewater from the Littleton/Englewood, Lakewood and Glendale plants) contributed the greatest amount of nitrogen, phosphorus and organic carbon produced within the 50th Avenue basin. For example, during the perioo of October 198D to September 1981, the upper and lower basin point sources combined contributed about 50 percent of the total vol ume of streiiTlflow at 50th Avenue. In other words, the wastewater-- effluent doubled the aver-age flow of the (ivet-. r'\.... uur- necessary to operate the Denver Northside plant. ing this period, about 90 percent of the total loads for both phosphorus and nitrogen were due to point source loading of the river from sewage pldnts, Similarly, about 70 percent of the total organic carbon load was due to