4.3 Water Quality

Goal 3 - Water Quality

Preserve, maintain and improve aesthetic, physical, chemical and biological composition of surface waters and groundwater within the District.

Discussion

The HHPLS used an extensive public input process to establish water quality goals for the primary receiving waters in the District, focusing primarily on identifying target total phosphorus concentrations.   In addition, Total Maximum Daily Load studies for four lakes in this subwatershed will establish phosphorus load reduction goals and strategies to reduce excess nutrient concentrations.  This plan identifies those phosphorus goals plus additional goals related to water quality and sets forth a set of actions the District will undertake to reduce pollutant loading in the subwatershed and achieve water quality goals.  The achievement of these water quality goals is not only necessary to meet state and federal water quality requirements and to prevent future TMDLs, but also to meet this plan’s ecological integrity goals. 

Desired Outcomes:  Achievement of in-lake nutrient concentration goals through achievement of nutrient loading reductions.

Metrics:

  • In-lake nutrient concentrations/Trophic State Index Scores (TSI) for the lakes within the subwatershed
  • Nutrient loading goals (lbs) for the lakes within the subwatershed

Goal 3.1 - Minnehaha Creek

Achieve in-lake total phosphorus concentration goals as identified in lake TMDLs and this plan.

Actions

  1. Partner with the Minneapolis Park Board and City of Minneapolis to investigate and implement potential internal load reductions identified in the Lake Nokomis, Powderhorn Lake, and Diamond Lake TMDLs.
  2. Amend existing or establish new District rules requiring greater than 50 percent phosphorus removal on new permitted development and redevelopment within the Minnehaha Creek subwatershed.
  3. Provide assistance to LGUs and developers to foster low impact development and redevelopment that minimizes new phosphorus and sediment loading.
    1. Develop and distribute model ordinances and design standards that incorporate low impact design principles.
    2. Sponsor educational opportunities for LGU staff, developers, elected and appointed officials and other interested parties to provide practical information and opportunities for sharing experiences.
  4. Promote the general application of BMPs across the subwatershed.
    1. Consider developing a small grant program to provide financial assistance to property owners desiring to retrofit their property with BMPs to reduce phosphorus and sediment loading.
  5. Continue partnering with the Minneapolis Park Board on regular water quality monitoring in the lakes to assess progress toward achieving the in-lake phosphorus goals. 
  6. Require LGUs to maintain or reduce phosphorus loading from developed uses as set forth in Section 5.6.1 of this plan within 10 years. 
    1. Provide education and training opportunities, technical and planning assistance for property owners and LGUs on methods to reduce phosphorus and sediment loading by incorporating BMPs into landscaping, infrastructure maintenance, and reconstruction.

Goal 3.2 - Minnehaha Creek

Achieve and maintain other state lake water quality standards including >1.4 m Secchi clarity and 14 ug/L chl-a for deep lakes, and >1.0 m Secchi clarity and 20 ug/L chl-a for shallow lakes.

Actions

  1. Undertake the actions specified in this Plan to achieve and maintain in-lake total phosphorus goals.
  2. Manage aquatic vegetation in accordance with a vegetation management plan that takes into account water clarity goals.
  3. Develop a water quality index which encompasses the District’s broader definition of water quality.

Goal 3.3 - Minnehaha Creek

Achieve and maintain an annual total phosphorus concentration in Minnehaha Creek of 80 ug/L, and maintain other parameters at ecoregion averages or better.

Actions

  1. Prepare a Minnehaha Creek Diagnostic Study to identify sources of phosphorus and sediment in the creek, and develop and implement strategies for improvement.
  2. Require LGUs to maintain or reduce phosphorus loading from developed uses as set forth in Section 5.6.1 of this plan within 10 years. 
    1. Provide education and training opportunities, technical and planning assistance for property owners and LGUs on methods to reduce phosphorus and sediment loading by incorporating BMPs into landscaping, infrastructure maintenance, and reconstruction.
  3. Based on the results of the Diagnostic Study, Biotic Integrity TMDL, and Stream Assessment, identify and construct projects to reduce existing non-point source pollution loading to the creek, focusing on areas close to the creek with little stormwater detention.  See Figure 20 for areas identified in the Stream Assessment as high priority for improvement.
  4. Inspect known erosion-prone areas of Minnehaha Creek at least annually to identify any new areas of erosion, and the entire creek at least every five years.
  5. In collaboration with riparian cities, agencies, and infrastructure owners improve degraded stream reaches for the purposes of bank stabilization, reducing sediment loads, preserving existing stream courses, improving habitat, and ecological enhancement.  See Figure 20 for areas identified in the Stream Assessment as high priority for improvement.
  6. In collaboration with riparian cities, agencies, and infrastructure owners spot repair identified erosion locations in Minnehaha Creek and develop strategies to prevent future erosion and sediment transport.
  7. Continue to investigate possible causes of periodic e.coli exceedances in Minnehaha Creek and develop strategies to address them.
  8. Continue to monitor water quality in Minnehaha Creek.