Key Changes To Proposed MPCA Construction Stormwater Permit

The Minnesota Pollution Control Agency (MPCA) has issued a draft NPDES/SDS permit to control pollution generated from runoff associated with construction activities discharging into waters of the State of Minnesota.The draft permit will replace the current general permit which will expire on August 1, 2018.

Some of the key revisions in the draft permit include:

Application and permit coverage effective date

MPCA is proposing to omit the mandatory 7 day waiting period. However, payment confirmation is required before the MPCA can issue permit coverage. The waiting period of “seven (7) calendar days” has been replaced with “upon completing the payment process”. All project proposers must obtain NPDES coverage electronically. The online application assures that all of the questions are completed and requires the user to certify that a SWPPP has been prepared for the project.

MPCA is also proposing to omit the mandatory 30 day waiting period. For projects that require a SWPPP review before coverage is issued, the MPCA will grant coverage upon the completion of the application and payment process and after the MPCA has made a determination that the SWPPP meets all of the permit requirements.
Stormwater Pollution Prevention
Plan content The requirements for SWPPP content have been re-written and re-ordered for clarity.

SWPPP Amendments

In order to prevent contractors from deviating from the SWPPP and selecting inappropriate BMP option with no regard to the specific site conditions, the MPCA has added the following language regarding SWPPP amendments: “All SWPPP changes must be done by one of the individuals described in item 21.4 or item 21.5 or another qualified individual. Changes involving the use of a less stringent BMP must include a justification describing how the replacement BMP is effective for the site characteristics.”

Documentation when the volume control standard cannot be achieved

For those projects where the full volume reduction requirement cannot be met on site, (e.g., the site has infiltration prohibitions), the permittee must document the reasons in the SWPPP.

Documentation of infeasibility

For projects adjacent to surface waters, the current permit requires the preservation of a 50’ buffer unless infeasible. For projects adjacent to special waters or impaired waters, a 100′ buffer zone must be preserved. The proposed permit requires permittees to document in the SWPPP why the buffer was not preserved.

Impaired waters and TMDL’s

This section was deleted. MPCA has made a programmatic decision not to include specific implementation activities or BMP’s in TMDL implementation plans for construction activity.

Permanent stormwater management

This section was deleted. The current permit offers permittees an option to follow a municipalities (or other plan approval authority such as a watershed district) stormwater ordinance in lieu of the permit requirements if that municipality is regulated by the state through the Municipal Separate Storm Sewer System (MS4) program. This provision was intended to reduce duplicate regulations as all regulated MS4 communities should have an ordinance in place that is at least as stringent as the state permit. However, MPCA’s determined many of the ordinances have not been written such that the requirements were at least as stringent as the state requirements and prevented the MPCA from taking any action if the permittees plans were approved by the municipality.

Permanent stormwater management

Projects that will result in a net increase in impervious surfaces of one acre or more must include plans for a permanent stormwater treatment system. Permittees are still expected to provide some type of volume reduction treatment if the site is conducive for stormwater infiltration. If the site is not conducive to stormwater infiltration (see item 16.14 through 16.22) other types of systems must be utilized such as a wet sedimentation basin. The permit will still offer flexibility for linear projects or projects where bedrock limits any type of stormwater management.

Infiltration prohibition

The proposed permit would prohibit infiltration systems constructed as part of the project regardless of whether or not the CSW permit requires stormwater management if the site receives runoff from vehicle fueling and maintenance areas.
Infiltration requirement The current permit requires “appropriate on-site testing consistent with the recommendations found in the Minnesota Stormwater Manual to verify soil types…”. The manual recommends a certain number of on-site soil tests depending on the size of the system. The proposed permit specifically requires permittees to provide at least one soil boring, test pit or infiltrometer test in the area of each infiltration system for determining infiltration rates. The proposed permit allows field tested rates to be used with a safety factor of 2 or permittees may use the infiltration rate chart found in the Minnesota Stormwater Manual to determine design infiltration rates based on soil type.

Infiltration prohibition

The current permit prohibits constructing infiltration systems in areas with contaminated soil or groundwater. The current language states that infiltration is prohibited in: “areas where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating stormwater.” The proposed permit includes additional language describing the steps permittees are expected to take to demonstrate compliance with this requirement. The proposed language is as follows:

“Permittees are prohibited from constructing infiltration systems where high levels of contaminants in soil or groundwater may be mobilized by the infiltrating stormwater. Permittees must either complete the MPCA’s site screening assessment checklist or conduct their own assessment to determine the suitability for infiltration. The assessment must be retained with the SWPPP. For more information and to access the MPCA’s screening assessment tool see the Minnesota Stormwater Manual”.

Infiltration prohibitions for Drinking Water Supply Management Areas (DWSMA)

The current permit prohibits infiltration anywhere within a DWSMA. The proposed permit limits the prohibition to “within an Emergency Response Area (ERA) as defined by the Department of Health” and “areas within a Drinking Water Supply Management Area (DWSMA) as defined in Minn. R. 4720.5100, subp. 13, classified as having high or very high vulnerability, unless a regulated MS4 Permittee has performed a higher level of engineering review sufficient to provide a functioning treatment system and to prevent adverse impacts to groundwater.”

Filtration systems

The following requirement has been added to the filtration system item: “The filter media must not be installed until the contributing drainage area has been constructed and fully stabilized unless rigorous erosion prevention and sediment controls (e.g., diversion berms) are provided to keep sediment and runoff completely away from the filtration area.”

Wet sedimentation basin requirement

A new requirement was added to the proposed permit requiring an impermeable liner to be included in the design of a basin located in active karst terrain.

Ditch stabilization methods

The current permit specifically states that some less effective stabilization methods such as mulch cannot be used in ditches or swales for stabilization and permittees must rely on more robust practices such as erosion control blankets. The proposed permit allows permittees more flexibility for the type of stabilization chosen for a ditch bottom if the slope is less than 2%. Additionally, as with all BMP requirements in the permit, If the selected BMP is found to be inadequate at minimizing erosion from ditches or swales, another more effective BMP must be utilized.

Sediment controls near stockpiles

The proposed permit specifically states that perimeter controls are required near the base of stockpiles. This change in language better clarifies that stockpile perimeter controls are required in addition to the perimeter sediment controls required in item 9.2. This does not represent a change in MPCA policy regarding stockpile management.

50 foot buffer

The current permit requires redundant sediment controls around surface waters if a 50 foot natural buffer cannot be maintained. The proposed permit requires that the sediment control practices must be spaced at least 5 feet apart. The MPCA believes that proper spacing for sediment storage between the practices is necessary in order to function properly. Language was also included to relieve permittees of the spacing requirement if there are site constraints.