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<br /> <br />OD2579 <br /> <br />As shown on figure 25, the computed DO concentrations exceed by more than <br />2 mg/L the existing limit of 6.0 mg/L for a type B1 stream classification. <br />Little increase in DO concentrations resulted from substituting augmented flow <br />conditions in the model simulation (fig. 25). <br /> <br />Profiles for both computed ammonia-nitrogen and nonionized ammonia-nitro- <br />gen concentrations for the two f10wconditions are shown on figure 26. The <br />model computed the ammonia-nitrogen concentrations, from which the nonionized <br />ammonia-nitrogen concentrations then were computed using the tables compiled <br />by Willingham (1976). An average value of 130C for water temperature was <br />assumed throughout the stream reach, and the median pH values for each of the <br />main-stem sampling sites observed during the 24~hour sampling period in <br />September 1975 were used. The results (fig. 26) show a maximum nonionized <br />ammonia-nitrogen concentration of 0.03 mg/L for augmented flow, conditions and <br />0.05 mg/L for nonaugmented flow conditions. Both concentrations exceed the <br />proposed 0.02-mg/L concentration for a type B1 stream classification for a <br />short distance downstream from the main wastewater-treatment plant at <br />Steamboat Springs. The exact length of stream in which the non ionized <br />ammonia-nitrogen concentration would exceed the proposed 0.02-mg/L standard <br />cannot be determined, because of the uncertainty of the decay-rate coefficient <br />for ammonia nitrogen and, also, because of the possible large use of ammon~a <br />nitrogen by different algal forms, discussed earlier. The results presented <br />above also can vary depending on the actual water temperature and pH values. <br />For example, considering an acceptable pH range from 6 to 9 and a water <br />temperature from 00 to 200C, the maximum nonionized ammonia-nitrogen <br />concentration could range from 0 to 0.11 mg/L for augmented flow conditions <br />and from 0 to 0.16 mg/L for nonaugmented flow conditions (table 4). <br /> <br />The computed concentrations of fecal-coliform bacteria for existing <br />conditions are shown on figure 27. The computed concentrations are signifi- <br />cantly less than the maximum of 1,000 co10nies/100 mL allowed for type B1 <br />stream classification (Colorado Department of Health, 1974).. The greatest <br />difference in computed coliform-bacteria concentrations based on augmented <br />versus nonaugmented flow conditions occurs upstream from the Elk River. <br /> <br />Proposed Regional Wastewater-Treatment Plant <br />with 1978 Standards for Effluent <br /> <br />The effects of discharge from the proposed regional wastewater-treatment <br />plant on the Yampa River were simulated using the U.S. Geological Survey model <br />for the following conditions: Permanent population for September 2010 and <br />Q7,10 flow of 28 ft3/s (0.78 m3/s), permanent population for September 2010 <br />and Q7,10 flow with 20 ft3/s (0.56 m3/s) flow augmentation, peak-daily popula- <br />tion for December 2010 and Q7,10 flow, and peak-daily population for ,December <br />2010 and Q7,10 flow with 20 ft3/s (0.56 m3/s) flow augmentation. Treatment- <br />plant effluent was assumed to meet the proposed standards for 1978 (table 5). <br />The Q7,10 flow was assumed for September and December because low-flow occurs <br />in both months in the Yampa River at Steamboat Springs (figs. 5, 6). The <br />median pH values obtained during the 24-hour data-collection effort were <br />assumed for both the September and December conditions. Water temperatures of <br /> <br />44 <br /> <br />