The City of Cheyenne hired Ayres Associates to develop a plan for ecological remediation of historic Lake Minnehaha in Holliday Park to restore the pleasant environment experienced by the park’s many visitors. The remediation plan addressed high phosphorus and nitrogen levels that promote blue-green algae blooms, water temperatures that exclude coldwater fish, putrid odors, and limited depth. Tasks included water quality sampling, sediment sampling, environmental analysis, preparation of a remediation plan, and locating a site for disposal of dredged materials.
Phase 1 of construction included dredging the 3-foot-deep lake to a depth of 8 feet. An island also was removed, and a water circulating machine called a GridBee was installed in the middle of the lake, providing a constant rippling of the water. These measures improve circulation, washing the shoreline and disrupting the algae cycle. Circulation also keeps the water from getting hot on the top and cold on the bottom and maintains dissolved oxygen levels.
For Phase 2 Ayres addressed stormwater pollutants entering Lake Minnehaha through rain events by designing best management practices for the storm sewer system upstream, keeping out sediment, trash, and oil. Phase 2 also extended a major storm drain system upstream of the lake along Duff Avenue to increase the amount of stormwater captured and detained in Lake Minnehaha, which provides increased water circulation as well as improved flood control in the residential neighborhoods north of Holliday Park.