F. Water Quality F. Water Quality

F. Water Quality

Water quality is defined by the Clean Water Act to include the chemical, physical and biological components of a surface water. Public drainage system projects have potential to affect water quality (both positively and negatively) within the drainage system and/or downstream, through a variety of different mechanisms, including changes in velocity and scour potential, depth and duration of high flows, altered vegetation, changes in nutrient and sediment delivery, and modifications of runoff volumes and peak flows. These mechanisms may affect delivery of sediment (suspended solids and/or bedload), phosphorus, nitrogen, other nutrients, other substances, and biological oxygen demand within the drainage system and/or downstream. Minn. Stat. § 103E.015 Subd. 1 requires the drainage authority to consider water quality before a drainage project (a new drainage system, an improvement of a drainage system, an improvement of an outlet, or a lateral) is established. It is recommended that the engineer begin this consideration during the preliminary design phase of the drainage project to accomplish the following:

• Identify the mechanisms related to the project that may affect water quality, including the potential for increased erosion and/or sedimentation in channels, wetlands, or other waterbodies;
  
• Evaluate (qualitatively or quantitatively) whether the project will result in a water quality impact via these mechanisms;
  
• As necessary, provide options to offset the effects of these impacts; and
  
• Make a recommendation to the drainage authority.
  

It is the responsibility of the drainage authority to evaluate and initiate appropriate methods for proper consideration of water quality impacts for a given drainage project. A list of questions helpful in considering water quality impacts has been provided in Appendix 8.

There are several statewide and regional water quality regulations, standards and goals that may be applicable to public drainage system projects. These include:

Construction Stormwater Permits

Under the Clean Water Act (CWA) and state law, a National Pollutant Discharge Elimination System (NPDES)/State Disposal System (SDS) Construction Stormwater Permit may be needed for a public drainage system project. This permit requires best management practices (BMPs) for erosion prevention and sediment control during construction.

Generally, construction activities including clearing, grading, and excavating that will disturb one or more acres of land requires coverage under a NPDES/SDS construction stormwater permit. However, disturbance of less than five acres for the purpose of routine maintenance to maintain the original line and grade, hydraulic capacity, and purpose of the drainage system is exempt if all of the following apply to the project:

1. The project will disturb less than five acres of land as part of the routine maintenance activity;
   
2. Clean out of a ditch will return the affected reach to the original line and grade, hydraulic capacity, and original purpose of the ditch;
   
3. Maintenance of the ditch is in compliance with state and federal wetland regulations; and
   
4. Appropriate BMPs are used for erosion prevention and sediment control to avoid transport of sediment and associated contaminants that would violate water quality standards downstream from the project area during maintenance and restabilization of the drainage ditch.
   

Drainage ditch repair or maintenance projects that will disturb five acres of land or greater are not considered routine maintenance and require NPDES/SDS construction stormwater permit coverage. A permit is also required for a public or private ditch project if:

• The project is to establish a new drainage ditch and will disturb one or more acres of land; or
  
• The project involves improvement of an existing drainage ditch and will disturb one or more acres of land; or
  
• The project involves repair by re-sloping of an existing drainage ditch and will disturb one or more acres of land.
  

Additional guidance on drainage project BMPs for construction stormwater permits is available here.

State Water Quality Standards

When an engineer is in the “consideration” process of Minn. Stat. § 103E.015, she/he will need to know the condition of the water quality of the drainage system as well as downstream waters. Minnesota Rules Chapters 7050.0221 through 7050.0227 specify water quality standards for waters of the state, classified into seven classes of water uses. If water quality standards are exceeded, the Clean Water Act requires that the water is listed as impaired.

Total Maximum Daily Load (TMDL):

Once a water is listed as impaired, a total maximum daily load (TMDL) must be prepared to determine the allowable point and nonpoint source pollutant loads to an impaired stream, reach or waterbody necessary to meet applicable water quality standards. The engineer should identify within the preliminary engineer’s report if the drainage project is within or upstream of an impaired water or within a watershed subject to a TMDL. The report should include a discussion on how potential increases in pollutant loading to impaired waters and those with TMDLs are considered and a recommendation to the drainage authority on any specific actions that should be taken.

Some drainage projects can result in the rerouting of runoff from one watershed to a neighboring watershed, resulting in the alteration of pollutant loads to the receiving water of the neighboring watershed. Such a change in loading may require a recalculation of total maximum daily loads for the receiving water.

Watershed Restoration and Protection Strategy (WRAPS):

In 2013, the Minnesota Legislature adopted amendments to Minn. Stat. 114D requiring that all major watersheds (HUC (Hydrologic Unit Code) - 8) have a Watershed Restoration and Protection Strategy (WRAPS). A WRAPS is a summary document that includes TMDLs, watershed assessment and biological stressor identification work, watershed and water quality modeling and monitoring, as well as summaries of other relevant projects and efforts in that watershed. The WRAPS provides a table that includes the implementation strategies needed to meet the water quality standards and a timeframe with interim milestones to achieve them.

The Engineer can assess the current status of these water quality documents, by major watershed on the MPCA website. The Minnesota Pollution Control Agency also maintains a list of TMDLs and WRAPS. Additional information regarding watershed planning is available in Appendix 13.

Statewide and Regional Reduction Goals:

The Minnesota Nutrient Reduction Strategy, adopted in September 2014, is a valuable tool for drainage authorities and engineers for consideration of water quality impacts. This strategy report provides nutrient reduction goals and milestones for the three major drainage basins in Minnesota, prioritizes problems and solutions, and provides general strategies for accomplishing these goals.

The Red River Basin Commission and the State of Minnesota have also developed flow reduction goals for two of the state’s largest river basins to achieve multiple long term goals including flood and nutrient reduction. These flow reduction goals include:

• A 20% peak flow reduction goal on the main stem of the Red River, for a flood equivalent to the 1997 spring flood; and
  
• A 25% reduction in the magnitude and duration of the two-year peak flow in the Minnesota River.