6.1.1 Regulation for Water Quality
Where lakes do not currently meet water quality goals, two key strategies for the achievement of load reductions are rules that are more stringent than those requiring removal of at least 50 percent of new phosphorus loads generated by new development on new permitted development and redevelopment, and management of volumes generated by that new development. A third strategy is a requirement for stormwater plan approval earlier in the development process. This Plan recommends the following options for consideration in regards to future regulatory requirements:
- Require a removal rate of more than 50 percent of new phosphorus loads on new development and redevelopment, or allow no net increase.
- Require abstraction of the first one inch of rainfall on new development and redevelopment.
- Require MCWD Staff review of concept plans to identify regulatory requirements, stormwater management alternatives, and critical natural resources to efficiently expedite review so the District may comment on proposals and how they relate to District water quality goals. MCWD intends to work cooperatively with developers in early stages of project development in order to identify opportunities and obstacles to permitting early in the process.
- Require developers to identify existing drain tile lines on property proposed for development.
Achieving improvement in lakes that are degraded from excess nutrient loading will require the combined efforts of the regulatory program, capital projects, and local initiatives. A majority of the lakes and major streams in the District have experienced some measure of degradation from development in the watershed. Development and the associated creation of new impervious surface changes hydrology and pollutant loading in the watershed in fundamental ways. Most notably, more stormwater runs off the site, and carries with it pollutants and sediment. These pollutants negatively affect water quality, decreasing water clarity, increasing algae blooms, and inhibiting ecological function.
Development also decreases the amount of stormwater that naturally percolates into the soil to recharge groundwater, thus reducing baseflow in streams, changing hydrology in groundwater-fed wetlands, and decreasing water availability in drinking water aquifers.
The current regulatory program requires development and redevelopment that meets certain size thresholds to provide pretreatment of stormwater before being discharged to water resources, whether on site or through some regional treatment method. Smaller developments are required to utilize Best Management Practices (BMPs) to the extent possible to reduce pollutant loading.
Increased phosphorus removal
This Plan includes for each subwatershed an analysis of the impacts of future development and redevelopment on water quality, and the impact of the current regulatory program. For each lake that does not currently meet its water quality goal, a phosphorus load reduction plan sets forth a plan of actions to achieve the water quality goals in that lake, and to prevent further degradation of the other lakes, streams, and wetlands. In many instances, the load reduction required is so great that all potential means of reducing phosphorus loading must be considered to find the most cost-effective balance of strategies. These plans assume that permitted new development and redevelopment will be required to achieve a much higher rate of phosphorus load removal than can be achieved through traditional stormwater management such as detention ponds. The HHPLS assumed that rather than specifying a more stringent removal rate of new phosphorus loading, new development would be limited to no net increase in phosphorus load, and the phosphorus load reduction plans reflect that standard.
Another key strategy to mitigate the effects of development is the adoption of an abstraction or infiltration standard for new development and redevelopment. Such a standard would require the abstraction (retention on site through infiltration, evapotranspiration, or capture and reuse) of one inch of rainfall. A common method of abstraction is infiltration. Infiltration of stormwater onsite reduces the amount of runoff from the site as well as helps to recharge groundwater.
Requiring new development and redevelopment to abstract some of the new stormwater generated and encouraging retrofitting to increase abstraction on existing sites would minimize new pollutant loading that would have been conveyed by that stormwater. Abstraction would be one of the primary tools new development would use to meet the proposed more stringent phosphorus load requirement.
An abstraction requirement would also reduce runoff volumes and help reduce future downstream erosion in streams and channels or flooding in landlocked basins. Approximately 70 percent of annual runoff volume in Minnesota results from precipitation events of 1” or less (MPCA, 2000). Controlling this volume on site reduces the downstream impact of new volume, minimizing the impact of this new volume on streamflow, potentially preventing new erosion problems and sediment transport. Increased infiltration would also help maintain groundwater levels, preserving wetland hydrology and stream baseflows.
Early review of concept plans
The proposed rule revisions requiring abstraction and an increased rate of phosphorus removal will require developers to consider stormwater planning earlier in the development process than is traditional. In many cases meeting rule requirements will take careful up-front planning to incorporate site design characteristics, traditional and nontraditional BMPs, native vegetation and tree conservation, and other Better Site Design and Low Impact Development techniques into the site plan. District staff can assist cities in providing technical assistance and advice early in the development process to help assure that both developer and public goals are balanced.