Overview

The purpose of the construction stormwater controls is to protect water resources from sediment and other pollutants.

The MPCA issues the Construction Stormwater General Permit to protect water resources from contaminants in runoff from construction sites. The general permit requires controls for construction stormwater runoff. In most cases, construction site owners and operators may apply for coverage under the general permit, meaning they agree to comply with the conditions set in the general permit.

The current permit expires on August 1, 2013. Because federal rules have changed since the last permit was issued in 2008, the MPCA must update the general permit to comply with these federal changes. Based on research and experience, the federal government continues to make changes to ensure that adequate best management practices are in place.

While the primary changes concern federal rules, the MPCA is also revising the permit to clarify existing language, better align with the municipal stormwater program, address defects, and incorporate changes needed to enhance compliance with the permit.

Also, the agency will require that permit applications be submitted electronically to achieve greater efficiency.

The MPCA is developing the Construction Stormwater General Permit with equitable access to all stakeholders. The agency will provide the public and permit-holders with ample opportunity to comment, including public meetings and a 45-day comment period, both of which exceed federal requirements. As demonstrated by past changes to permits, the MPCA values comments and incorporates valid suggestions into the final permit.

The draft Construction Stormwater General Permit was open for public comment from Feb. 4 – March 20, 2013. The draft permit and supporting documents for the permit are provided below, followed by an outline of changes to the current permit.

Links

• MPCA Public Notice for the draft Construction Stormwater General Permit
• Draft of Construction Stormwater General Permit (wq-strm2-68a)
• Detailed fact sheet outlining changes to the draft Construction Stormwater General Permit (wq-strm2-68b)
• Handout from the Dec. 17, 2012 stakeholder meeting (wq-strm2-68c)
• Sign up for Construction Stormwater email updates
• Links to Documents from the U.S. E.P.A. regarding Construction Stormwater:
  
  • Final 2012 Construction General Permit (CGP)
  • Final 2012 Construction General Permit (CGP) – Fact Sheet
  • 40 CFR Part 450—Construction and Development Point Source Category (C&D Rule) 2009
    
    

Changes to the Minnesota Construction Stormwater general permit

BMPs protecting surface waters include mulch and silt fences.

In December 2009, the U.S. Environmental Protection Agency (EPA) proposed a numeric effluent limitation in its Construction and Development rule for runoff from construction sites. The numeric limit was based on the allowable level of turbidity, which is a measure of sediment in water runoff from a construction site.

Originally, the Construction and Development rule required monitoring runoff from the site by collecting samples to test whether the site was complying with the limit. However, due to problems identified with the data used to calculate the numeric limit, the EPA delayed this requirement until new data are available. Therefore, there will be no numeric turbidity limit or monitoring and reporting requirements for turbidity in the MPCA 2013 general permit.

However, the MPCA is required to address certain enhanced Best Management Practices (BMPs) known as non-numeric effluent limitations in order to prevent the mobilization of sediment and limit the generation of dissolved pollutants from construction sites.

For more information on the Construction and Development requirements, visit the EPA website.

To comply with the federal Construction and Development rule, the MPCA plans to address the new requirements in the Minnesota 2013 general permit as follows.

Site considerations during construction:

Natural vegetative buffer helps filter sediment from runoff.

• Maintain a 50-foot natural buffer or use redundant sediment controls near surface waters if a buffer is not feasible.
• Control flow rates and the total stormwater volume from the site to minimize downstream impacts.
• Use conveyance channels to route water around un-stabilized areas, including erosion controls and velocity dissipation devices to limit the potential for erosion.
• Direct discharges from stormwater controls to vegetated areas and use velocity devices if necessary to prevent erosion.
• Minimize the disturbance of slopes 3:1 or steeper.
• Initiate soil stabilization immediately by taking action as soon as practicable, but no later than the end of the next work day when earth-disturbing activities will cease for at least 14 days.
• Minimize soil compaction and preserve topsoil at the site.
• Temporary sediment basins outlet structure must be designed to withdraw water from the surface.
• Sediment basins must be located outside of any natural buffers.

Design of stormwater controls:

• The BMPs in the Stormwater Pollution Prevention Plan (SWPPP) include requirements to control both peak flow rates and total stormwater volume at basin outlets and other water channelized from the site to minimize downstream channel and streambank erosion. Therefore, factors to be considered in design of controls include:
  • Stormwater runoff and run-on at the site.
  • Expected flow from impervious surfaces, slopes and site drainage features.
  • The expected amount, frequency, intensity and duration of precipitation.
• The SWPPP will also need to address the range of soil particle sizes expected at the site.

Pollution Prevention (P2) measures: 

Storage areas for building materials and other products must minimize exposure to stormwater

Construction materials

• All potential pollution generating activity locations, such as chemical storage, washout activities, fueling areas, etc. will need to be shown on the SWPPP site map.
• Storage areas for potential pollutants on the site, such as building materials, hazardous products or materials, soaps, detergents, wastes, etc. must minimize exposure to stormwater.
• All liquid and solid wastes generated by washout operations (concrete, stucco, form release oils, curing compounds and others) at the site must be contained for treatment or proper disposal.
• The SWPPP must have a fueling operation plan and emergency spill plan.
• Portable toilets on the site must be secured and sanitary waste must be properly disposed of.

Holding stormwater water in cisterns to use for irrigation is one way to retain stormwater on-site.

The MPCA is also considering changes to improve permanent stormwater treatment to address state anti-degradation requirements, clarify existing language, remove redundancy and enhance compliance with the permit. Notable changes include the following:

• That all permit applications are submitted electronically with permit coverage within 7 days.
• That trained individuals attend refresher training every 3 years.
• Site inspection requirements, including after a rainfall event greater than ¼ inch (rather than the current ½ inch) in 24 hours.
• That 1 inch of stormwater runoff from new impervious will be held on site via infiltration, harvesting or reuse, unless prohibited.
• That chemicals used for purposes of flocculation will be documented in the SWPPP and that a chemical treatment plan will be included for the site.
• That filter backwash waters are properly disposed of or returned to the beginning of the treatment process and that filter media at the site are maintained and cleaned.
• That soils are stabilized within 24 hours for activities that are adjacent to and drain to public waters (as designated by the Minnesota Dept. of Natural Resources) with restrictions during fish spawning times.
• The permit will allow projects located in an NPDES-permitted MS4 community to follow the current MS4 permit permanent treatment requirements.
• The previous permit requirement for a DNR approval letter for discharges to calcareous fens was deleted from the draft permit and Appendix A BMPs applied.

See the detailed fact sheet above for more information about these changes.