MCWD Lakes TMDL – Lake Nokomis, Parley Lake, Lake Virginia, Wassermann Lake

Four lakes in the Minnehaha Creek Watershed District (MCWD) that are on the EPA's 303d list of impaired waters due to excess nutrients (total phosphorus) are the subject of this study. These lakes are Lake Nokomis (27-19), Parley Lake, (10-42), Lake Virginia (10-15), and Wassermann Lake (10-48). The initial work on this TMDL study included five other lakes in Minneapolis: Brownie Lake, Powderhorn Lake, Diamond Lake, Lake of the Isles and Lake Hiawatha. They have been removed from the project for various reasons. Brownie was removed because a review of the in-lake data indicated that it is meeting water quality nutrient standards and has been removed from the list of impaired waters. Powderhorn was likewise removed because a review of the in-lake data indicates that it is meeting water quality nutrient standards (however, additional years of data are needed to confirm the trend in the data before an official removal from the list of impaired waters is done). Diamond was removed because an evaluation was done by MPCA that indicated that it functions more like a wetland than a shallow lake and, therefore, shallow lake water quality standards do not apply to it. Lake of the Isles was listed prior to the establishment of shallow lake water quality standards and was removed because it is meeting those standards. Lake Hiawatha was removed from this project and incorporated into a separate TMDL project that encompasses impairments to Minnehaha Creek, which drains into Hiawatha. The four listed lakes are all classified as Class 2B, 3C, 4A, 4B, 5, and 6 waters. The most protective of these classes is Class 2 waters, which are protected for aquatic life and recreation. The state eutrophication standards for these lakes are in the following table. A request is being made to EPA to set site-specific standards for Lake Nokomis. This TMDL considers both the eutrophication standards and the requested site-specific standards as dual endpoints for Lake Nokomis. The TMDL will be calculated based on both of these endpoints, to allow for either to be implemented after the standards are finalized. The Lake Nokomis watershed is dominated by single family residential neighborhoods, with areas of park and recreation, commercial, and industrial land uses. Wassermann Lake is located within the Parley Lake watershed, with land use primarily agricultural, undeveloped, and parkland. Residential and commercial land uses within this watershed are primarily confined to the City of Victoria. The Lake Virginia watershed includes single family residential, parkland, and other open space. The area directly surrounding Lake Virginia is predominantly single family residential. Phosphorus is identified as the primary pollutant leading to eutrophication in these lakes. The phosphorus sources include stormwater runoff, internal loading, and atmospheric deposition. Phosphorus loads from stormwater runoff were estimated using the Simple Method, which uses stormwater runoff volume and total phosphorus event mean concentrations. Loads from stormwater runoff were estimated separately for runoff from regulated (municipal separate storm sewer system (MS4) entities, from the Metropolitan Airports Commission (MAC), and nonregulated runoff). Internal loading was estimated using a mass-balance approach with a lake response model. Loads from atmospheric deposition were estimated using average regional rates. The loading capacity for each lake was calculated using Bathtub, an empirical model of reservoir eutrophication developed by the U.S. Army Corps of Engineers. The models were calibrated to existing water quality data, and then were used to determine the phosphorus loading capacity of each lake. An implicit margin of safety (MOS) was incorporated by using conservative assumptions. Individual wasteload allocations (WLAs) were set for each regulated MS4 source, including regulated stormwater runoff from the municipalities, the road authorities (Hennepin County, Carver County, and Mn/DOT), and MCWD. An individual WLA was also set for the portion of the MAC that drains to Lake Nokomis. Categorical WLAs were set for construction stormwater and industrial stormwater. One load allocation was set for each lake. The load allocation includes phosphorus sources from stormwater runoff not regulated by an MS4 permit, internal loading, atmospheric deposition, and any other unidentified loads. Lake Nokomis is a eutrophic lake. To meet the state eutrophication standards, an overall phosphorus load reduction of 57% is needed. To meet the requested site-specific standards, the reduction drops to 35%. Parley Lake is a eutrophic to hypereutrophic lake. To meet the state eutrophication standards, an overall phosphorus load reduction of 44% is needed. Lake Virginia is mildly eutrophic. To meet the state eutrophication standards, an overall phosphorus load reduction of 20% is needed. Wassermann Lake is a eutrophic to hypereutrophic lake. To meet the state eutrophication standards, an overall phosphorus load reduction of 62% is needed. A series of stakeholder meetings were held. Cities, counties, agencies, and park districts were invited to provide input into the project approach and to review draft documents. Public meetings were held to provide information to the public about the project and to solicit input regarding background information and implementation recommendations. The approach to implementation will include and augment, where needed, actions and strategies in the MCWD Comprehensive Watershed Management Plan (MCWD Plan), approved by the MN Board of Water and Soil Resources and adopted by the MCWD Board of Managers in 2007. The MCWD Plan outlines a framework for water resource management including requirements for local government units. In addition, the MCWD has also adopted rules that regulate activities in the watershed and strive to prevent pollution. Watershed-wide activities and activities specific to the individual lakes are included. A detailed implementation plan for the lakes in this study is in progress. The monitoring plan includes recommendations for standard in-lake monitoring, as well as additional recommendations for biological monitoring where time and budget allow.
Date Issued
Number of Pages
Rights Holder
Minnesota Water Research Digital Library
Rights Management
Creative Commons