Water Quality of Fountain and Monument Creeks

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009 Dissolved Oxygen When considerable oxygen demand is present in a stream such as Fountain Creek, dissolved oxygen may be substantially depleted while digestive proces- ses are occurring. However, the dissolved- oxygen concentrations, which were measured in Fountain Creek during the daylight hours and, therefore, are likely to be somewhat larger than the minimum daily dissolved- oxygen concen- tration, indicate that the stream generally is well oxygenated (fig. 16). Since 1975, only four dissolved- oxygen measurements were less than the recom- mended standard of 5.0 mg /L for Lower Fountain Creek. The stream remains well oxygenated probably because of large reaeration rates that result from large velocities and shallow depths in Fountain Creek. Monthly variations in dissolved - oxygen concentrations of Fountain Creek at sites F12, F17, and F36 are summarized in figure 17. Because dissolved - oxygen concentration is inversely related to water temperature, the smallest dissolved- oxygen concentrations of Fountain Creek occur during July and August when water temperatures are warmest and biological decomposition is greatest (fig. 11); the largest dissolved- oxygen concentrations occur during December and January when water temperatures are coldest and biological decomposition is least. Suspended Solids The suspended- solids concentrations at nine sites along Fountain Creek from 1975 through 1983 are summarized in figure 18A, and suspended- solids concentrations from 1980 through 1983 are summarized in figure 18B. Down- stream variations in suspended- solids concentrations are better represented in figure 18B because the period of record and the number of measurements are more similar between sites. The suspended- solids concentrations measured on Fountain Creek upstream from the confluence with Monument Creek have been small because of the pres- ence of nonerosive igneous and metamorphic rocks, the cobbled -bed channel, and the shallow soils in the Upper Fountain Creek basin. The small concen- trations of suspended solids result in a clear stream, which adds to the aesthetic quality. However, suspended- solids concentrations rapidly increase downstream from the confluence with Monument Creek primarily as the result of Monument Creek inflow, as indicated by data collected at site F17. Suspended - solids concentrations decreased from site F17 to site F19 because of dilution from the Colorado Springs Wastewater Treatement Plant effluent. The median suspended- solids concentration (1980 -83) decreased from 156 mg /L at site F17 to 89 mg /L at site F19 (fig. 18B), which is located about 2 mi downstream from the wastewater - treatment plant outfall. However, the resulting increase in streamflow from the effluent re- entrains sediments that have been deposited in the stream channel downstream as the result of tributary inflows, which increases the suspended- solids concentrations downstream from site F20 (fig. 18B). 29