Conclusions
Urban hydrology seems to be influencing water quality in the South Platte River in the Denver metropolitan area. Water quality generally decreased as the river moved through the Denver metro area. In addition, the second hotspot location (28 km – 37 km) is in the urban heart of the city with the highest concentration of storm drains and the highest degree of impervious surface. In the fall and winter when natural flow is lowest, water quality reached its lowest levels. During these times of the year, the majority of flow is from treated wastewater, which suggests that it may be strongly influencing water quality in the South Platte River.
While it is beyond the scope of this paper to identify specific sources of water pollution in this system, we were able to make some reasonable conjectures. It appears that wastewater treatment facilities may be one of the main sources of nitrogen and phosphorus pollution in this system. However, not all facilities are releasing similar concentrations of these pollutants. Some facilities, such as Robert W. Hite Treatment Facility seem to be treating their effluent to fairly low levels prior to discharge. It also seems likely that industrial activity may be an important source of pollution in isolated areas. For example, at the third hotspot area (47 km – 48 km), there are a number of industrial properties including the Suncor Commerce City oil refinery.
Most of the samples collected in this study exceeded state limits for nitrogen and/ or phosphorus concentrations. These elevated levels may be leading to other undesirable downstream effects, such as eutrophication. The river was mostly in compliance with state regulations in terms of DO and temperature, although the temperature standard is for a warm-water stream and many desirable fish, including Oncorhynchus myki ss (rainbow trout) and Salmo trutta (brown trout) are unlikely to survive long-term in this system unaided. Urban hydrologic systems are complex and improving water-quality may be difficult. However, tightening of water-quality standards, especially for wastewater treatment facilities, could result in positive changes to this system.