Engineering Solutions for Lake Water Quality Improvement

Lake Nokomis, part of the chain of Lakes in Minnesota, has experienced degraded water quality due to high phosphorous loading over time. The Minnehaha Creek Watershed District, the governing body for water resources related issues for the area, has funded a multi-component project focused on improving the water quality in the lake. The project components include constructed wetlands and grit chambers to treat runoff from surrounding residential neighborhoods, an inflatable weir to prevent Minnehaha Creek water from flowing back into the lake, and rough fish removal and Alum treatment to reduce the internal phosphorous loading. Design and construction of the project faced many obstacles due to physical restrictions from park land use, tree protection, and existing city utilities, and environmental and regulatory issues. A voluntary Environmental Assessment Worksheet by the Watershed District forced an extensive permitting effort. The historic significance of the park system and tree protection called for creative wetland design. The age, and sometimes inaccurate, location information of the existing utilities created further problems during construction. Construction was scheduled for winter to reduce the obstruction to recreational activity at the park, which caused some difficulty during construction due to extreme cold conditions on some days. The watershed district and the engineering team had to conduct an extensive public relations campaign during construction, as Lake Nokomis is a very popular recreational area even during the winter months. Many joggers and walkers had to be made aware of the dangers associated with a construction site. The location and nature of urban construction, as well as the many environmental and regulatory issues, forced the project team to develop quick and innovative solutions to successfully complete the project on time and on budget.