Construction stormwater permit overview

Construction stormwater permit overview

A technical summary of Minnesota’s NPDES permit

This fact sheet provides summary information. Please review the NPDES/SDS Construction Stormwater General Permit for more detailed information. Ecological harm

By following the terms and conditions of the construction stormwater permit, Minnesota’s construction workers reduce the environmental pressure of earth-moving activities on Minnesota’s water.

In days or weeks, land disturbing activities at construction sites has the potential to contribute more sediment to streams than is deposited naturally over several decades. The environmental damage is severe and often permanent. Polluted runoff clouds streams, harming or killing fish and other aquatic organisms. Sediment deposits accelerate filling-of lakes. Sediment also carries nutrients that cause excessive plant growth and algae that contribute to the eutrophication process. Increased volume of runoff caused by the creation of new impervious surfaces can cause severe erosion in receiving waters and may change the contours of a river and wipe out valuable habitats like gravel stream beds which are necessary for fish spawning. Other pollutants at construction sites such as concrete wash water, petroleum products, chemicals, construction materials and sewage may pose a risk to both surface and groundwater and need to be properly handled and stored.

Regulatory mandate

Minnesota’s construction stormwater permit is an extension of the National Pollutant Discharge Elimination System (NPDES) Stormwater Program, which is part of the Federal Clean Water Act.

The NPDES Stormwater Program is a comprehensive national program for addressing polluted runoff. The U.S. Environmental Protection Agency (EPA) is ultimately responsible for the quality of the nation’s water, but in Minnesota, the Minnesota Pollution Control Agency (MPCA) administers this federal program as well as the related State Disposal System (SDS) permit program. The states combined NPDES/SDS construction stormwater permit fulfills federal and state requirements by requiring permittees to control runoff.

Enforcement

The federal government requires NPDES permit coverage of construction sites that disturb one or more acres. Sites that lack permit coverage and/or fail to meet permit terms and conditions will be subject to MPCA enforcement action, civil penalties and/or criminal charges. Owners and operators of construction activity that fail to obtain permit coverage are open to third-party civil suits.

Application process

Prior to submitting an application, regulated parties must develop a complete and accurate Stormwater Pollution Prevention Plan (SWPPP) in accordance with the stormwater discharge design requirements in Part III and Part IV of the permit. The construction stormwater permit application must be submitted using the MPCA Online Services system along with electronic payment of the $400 application fee.

The application fee can be submitted online via credit card or e-check. Instructions for completing the application process can be found at the Steps to Construction site. Permit coverage is effective seven calendar days after submitting a complete application. An authorized party, such as a consultant or legal counsel, may complete the application for the project owner. Both the owner and the contractor must be listed on the application.

If the applicant is unable to apply online due to lack of internet access or other reasons, the MPCA can be contacted at 651-757-2119 or 800-657-3804 for assistance to receive a waiver and instructions for obtaining a paper application form.

Projects that are not eligible for permit issuance within seven days for sites disturbing 50 acres or more where stormwater will discharge within a mile to special waters or to impaired waters, the application and SWPPP must be submitted for review at least 30 days prior to construction.

Special waters are described in Appendix A part B of the permit and are Outstanding Resource Value Waters (ORVW), including calcareous fens, trout lakes and trout streams. The permit also describes impaired waters as those waters identified as impaired under section 303 (d) of the Federal Clean Water Act and are impaired for at least one of four construction related impairments of phosphorus (nutrient eutrophication biological indicators), turbidity, dissolved oxygen or aquatic biota (fish bioassessment, aquatic plant bioassessment and aquatic macroinvertebrate bioassessment).

The MPCA has an online map tool that can be used to determine if the site is within one mile of a special or impaired water. The distance is measured using a straight line (aerial radius measurement) not the flow distance from the closest project discharge point to the nearest edge of the water body.

Stormwater Pollution Prevention Plan requirements

Your SWPPP must meet all terms and conditions of Part III and IV in the permit including a description of all erosion prevention and sediment control Best Management Practices (BMPs) to be utilized on the site to control sediment and other pollutant discharges from the site. The SWPPP must be prepared by an individual who is knowledgeable and trained in the preparation of SWPPPs. The SWPPP must be a combination of narrative, plan sheets and standard details that include the following components:

• A description of the construction activity and potential for sediment and other potential pollutant discharges from the site.
• The identity of an individual(s) (once known) to oversee BMP implementation, installation and conduct inspection and maintenance activities.
• A chain of responsibility between the owner and contractor and all operators at the site to ensure the SWPPP is implemented.
• Training documentation for all individuals required to be trained in associated duties in relation to the SWPPP.
• Stormwater design specifications and calculations for stormwater management systems, including the number of acres of existing and new impervious surfaces.
• Timing of installation for all erosion prevention and sediment control BMPs and permanent stormwater management systems.
• Location and type of all BMPs to be utilized at the site along with procedures to establish additional BMPs as necessary.
• Estimated quantities of all BMPs to be used for the life of the project.
• A site map showing both the existing and final grades, including direction of flow and pre and post drainage area divides. The site map must also include locations of steep slopes, impervious surfaces, soil types, and potential pollutant-generating activities (such as building products, pesticides, herbicides, fertilizer, treatment chemicals, hazardous materials, solid waste, portable toilets, etc.).
• Areas not to be disturbed on the site, including the location of any required buffer zones.
• Locations of areas to be phased to minimize duration of exposed soils.
• Maps showing the locations of all surface waters, including wetlands, stormwater ponds or basins within one mile of the site. The site map must also show areas of the site that will drain to a public water the Department of Natural Resources (DNR) has promulgated “work in water restrictions” for fish spawning timeframes.
• A determination whether surface waters within one mile of the site are special or impaired for one of the construction-related parameters.
• Final stabilization methods for exposed soils.
• The following factors must be accounted for in design of BMPs:
• Amount, frequency, intensity and duration of precipitation.
• Stormwater runoff and run-on, including expected flow from impervious surfaces, slopes and site drainage features.
• How flow rate and volume of channelized flow will be managed to minimize erosion at outlets and downstream erosion.
• Range of soil particles expected at the site.
• Methods to minimize soil compaction and preserve top soil at the site.
• A maintenance plan for permanent stormwater treatment systems, including who will maintain the system.
• Plans for proper use of sediment treatment chemicals (polymers, flocculants, etc.) in accordance with Part IV.C.10 of the permit.
• Documentation why certain design requirements or SWPPP components are not feasible (as allowed in the permit) and the method that will be substituted to comply with permit.
• Stormwater pollution mitigation measures to be utilized as a result of an environmental review.
• Additional or different measures needed at the site to address karst or drinking water supply management areas.
• Identify temporary sediment basins, if more than ten acres are disturbed and drain to a single point of discharge.
• Identify dewatering and basin draining practices.
• Identify inspection and maintenance practices.
• Identify pollution prevention management measures.
• Include a strategy for retaining records.
• Describe the timing of BMP installation.
• Location and type of temporary and permanent BMPs.
• Include standard plates and specifications of BMPs.
• Additional requirements if the receiving water is impaired for phosphorous, turbidity, dissolved oxygen or biotic impairment, or measures needed to comply with any Total Maximum Daily Load (TMDL) that has been established.

Stormwater Pollution Prevention Plan amendments

Amendments to your SWPPP are required when:

• There is a change in design, construction, operation, maintenance, weather or seasonal conditions that effect potential discharge of pollutants.
• Inspections indicate BMP ineffectiveness.
• General objectives for minimizing pollutant discharges or terms and conditions of permit are not being met.
• The MPCA determines that the project’s discharges may contribute to non-attainment of a water quality standard, does not meet requirements for impaired waters, TMDLs with implementation requirements or that the SWPPP is not meeting one of the above determinations.

Permanent stormwater management system

Pervious pavers

When a project replaces vegetation or other pervious surfaces with one or more acres of cumulative impervious surface, one inch of runoff from the new impervious surfaces must be retained on site through infiltration or other volume reduction methods.

If infiltration is not allowed due to wet soils, bedrock, industrial contaminates, karst or other prohibitions listed in Part III.D.1.k. of the permit, then other methods of volume reduction must be considered and if some volume reduction is achieved, any remainder of the one inch volume must be treated prior to discharge by methods such as the following:

• wet sedimentation basin
• filtration system
• regional pond
• combination of infiltration and another practice or equivalent method

The permanent stormwater management system chosen for the project must be designed and constructed according to the parameters listed in the permit.

Erosion prevention practices

• Erosion prevention practices must be selected, installed, and maintained according to the manufacturers specifications and accepted engineering practices. Regulated parties choose which practices are best for specific sites. In addition, efforts must be made to minimize erosion through use of construction phasing.
• vegetative buffer strips
• minimization of land disturbance
• horizontal-slope grading
• avoiding disturbance of steep slopes or implementing slope draining, terracing, etc. to reduce erosion of steep slopes
• routing water around exposed soil areas

The permittee must take action to stabilize exposed soils, including soil stockpiles, whenever it is known that land disturbing activity on any portion of the site will cease for 14 days or more. The stabilization must be initiated immediately and completed within 14 days. If the site has exposed soils that drain into a public water with Minnesota DNR “work in water restrictions” due to fish spawning time frames, the soils in that portion of the site that drain to and are within 200 feet of the water edge must be stabilized within 24 hours. Examples of soil stabilization include the following:

• mulches
• hydraulic soil stabilizers
• erosion blankets
• rip rap
• sod

Other required erosion prevention practices:

• Conveyance channels must be used to route water around exposed soil areas unless infeasible.
• Velocity dissipation devices, such as check dams, sediment traps, or rip rap must be used in conveyance channels and at any outlet to reduce flow velocity.
• The last 200 feet of normal wetted perimeters of ditches or swales must be stabilized within 24 hours of connecting to a property edge or point of discharge. The remainder of the ditch or swale must be stabilized within the 14 day time frame. Acceptable methods for stabilizing ditches and swales include the following:
  • erosion control blankets or mats
  • rip rap
  • other material suitable for concentrated flow areas
  • mulch, hydromulch, tackifier, polyacrylamide or similar erosion prevention practice is not an acceptable stabilization method in these areas.
• Pipe outlets require energy dissipation, such as rip rap, splash pads or other suitable material to prevent scour and must be installed within 24 hours of connection to a surface water.
• An effort must be made to direct stormwater runoff to vegetated areas of the site.

Sediment control practices

Sediment control practices must minimize sediment from entering surface waters, curb and gutter systems, and storm sewer inlets. Regulated parties choose which practices are best for specific sites and practices must be installed according to permit timelines. Sediment controls to be used at the site include: Down gradient perimeter control established below the planned land disturbance and up gradient of vegetative buffers before work begins. Floating curtains are not an acceptable method of perimeter control near surface waters unless the work is on the shoreline or below the water line prohibiting the use of standard perimeter control and the floating curtain is located in the water as close to the shore as possible.

• Storm drain inlet protection.
• Sediment controls installed at the perimeter of temporary soil stockpiles.
• BMPs, such as stone pads or wash racks installed at construction exits to prevent vehicle tracking.
• Temporary sediment basins where ten or more acres of exposed soil drain to a common point on the site.
• Methods to minimize soil compaction.
• Maintaining a 50 foot natural buffer down gradient of the site or redundant sediment controls if buffer is not feasible, when the construction is within 50 feet of a surface water.
• Use of sediment treatment chemicals, such as flocculants and polymers, must comply with the following:
  • The chemical may only be applied to a sediment control system that provides filtration or settlement prior to discharge.
  • The chemical must be selected based on soil type.
  • The chemical must be used according to the manufacturer specifications and accepted engineering practices.

For sites within one mile of special or impaired waters, additional BMPs are required.

Additional BMPs are listed in Appendix A for the specific water of concern. Dependent upon the water listed these BMPs may include: Temporary erosion protection or permanent cover over exposed soil must be initiated immediately and completed no later than seven days after an area is no longer being worked.

• Temporary sediment basins are required where five or more acres of exposed soil drain to a single point.
• The permanent stormwater management system designed to retain one inch of runoff on the site.
• 100 linear feet permanent buffer zone must be maintained when the site is near a special water unless encroachment is necessary to complete the construction. In that case, redundant BMPs are required to minimize impacts.
• The permanent stormwater management system must utilize temperature controls when the receiving water is a trout stream such as shading, filtered bottom withdrawal, infiltration or other volume reduction practice.

Special waters are listed in Appendix A of the permit and include calcareous fens. Impaired waters for purposes of this permit are only those waters impaired for phosphorous, turbidity, dissolved oxygen and aquatic biota impairments. These impaired waters can be identified using MPCA’s Special and Impaired Search Tool.

Dewatering and basin draining

Dewatering and basin draining must discharge to a temporary or permanent sedimentation basin whenever possible. Dewatering must:

• Prevent erosion and scour at discharge points through the use of an energy dissipation device.
• Use an oil-water separator if the dewatering water contains oil or grease.
• Haul backwash water away for disposal if filters are used with backwash water