Horsetooth Water Quality Study

Horsetooth Reservoir is one of three large C-BT Project reservoirs on the East Slope. Several water providers, including Fort Collins, Greeley and the Soldier Canyon Filter Plant take water directly from Horsetooth into their treatment plants for municipal, domestic and industrial needs.
In 2006, the Colorado Water Quality Control Commission listed Horsetooth Reservoir as impaired due to low levels of dissolved oxygen. Since that time Northern Water, Horsetooth Reservoir water users and the Colorado Division of Wildlife have worked to identify the causes of oxygen depletion and to assess any impacts on aquatic life.

Dissolved oxygen is important for maintaining aquatic life and protecting the aesthetic qualities of water. Dissolved oxygen concentrations are also a gauge of existing water quality.

Water Quality Model
During the summer of 2009 Northern Water collected water quality data. Fort Collins, Greeley, the Soldier Canyon Filter Plant and Northern Water are now developing a water quality model to better understand Horsetooth’s water quality dynamics.
  
Water Quality Concerns
A variety of water quality concerns have arisen at Horsetooth over the years, including:

  • Low metalimnetic dissolved oxygen levels in late summer
  • Manganese releases from bottom sediments under anoxic conditions
  • Taste and odor problems
  • Increasing trends in total organic carbon

Water quality monitoring at Horsetooth has occurred for more than 20 years. In the summer of 2009 a new monitoring program began collecting data in the metalimnion (the middle layer of a thermally stratified reservoir) to help determine the cause of oxygen depletion and the extent of its impact on aquatic life.

Horsetooth Reservoir
Horsetooth Reservoir

Study ObjectivesCurrently underway, the Horsetooth Water Quality Study will analyze 2009 metalimnion data to identify processes driving the reservoir's dissolved oxygen levels. A second objective of the study is to develop a Horsetooth water quality model to:
  • Accurately mimic the reservoir’s existing water quality conditions and dynamics
  • Better understand the reservoir’s limnological processes and possible reasons for low dissolved oxygen
  • Investigate the impact of reservoir hydrodynamics and operations on water circulation, water quality transport, and water age