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.