The Municipal Separate Storm Sewer System (MS4) permit requires the permittee to conduct site plan reviews. Permittees must perform and document site plan reviews for construction projects that disturb one acre or more of land. The site plan review ensures active and post-construction requirements of a permittee's regulatory mechanism (e.g. code, ordinance, law) are met. The MS4 Permit requires the regulatory mechanism to be as stringent as the MNR100001/Construction Stormwater Permit.
This permit requirement is somewhat vague and has led to people not realizing that they need to review plans for specific items. The items identified below are the minimum that must be evaluated during a stormwater site plan review under the MS4 and Construction Stormwater Permits. For each site plan review performed, permittees must document the project name, location, total acreage to be disturbed, owner and operator of the proposed construction activity, and any stormwater related comments used to approve or deny the project. If you’d like to conduct a more comprehensive review, please see the MPCA’s Stormwater Pollution Protection Plan (SWPPP) Checklist. During the site plan review, you must verify that site plans include the information listed on this page.
(1) BMPs to minimize erosion
(2) BMPs to minimize the discharge of sediment and other pollutants
(3) BMPs for dewatering activities
(4) Site inspections and records of rainfall events
(5) BMP maintenance
(6) Management of solid and hazardous wastes on each project site
(7) Final stabilization upon the completion of construction activity, including the use of perennial vegetative cover on all exposed soils or other equivalent means
(8) Criteria for the use of temporary sediment basins
|Stabilization schedule must be no less than:|
|14 days for all exposed soils|
|7 days if a discharge point is within one mile of a special or impaired water|
|24 hours for areas within 200 ft of a public water during fish spawning times|
|24 hours for areas of ditches and swales within 200 ft of the property edge or surface water discharge point and 14 days for remainder|
BMPs to minimize erosion are the first line of defense for protecting stormwater from sediment running off your site. Soil without proper erosion control, such as blanket, mulch, or vegetation is prone to erosion. When reviewing site plans, ensure effective erosion control methods are described and located in the appropriate areas.
For more information on site stabilization see this page.
Properly installed and maintained sediment control BMPs, such as silt fence or bioroll, prevent sediment from discharging from your site. They allow stormwater to pass through, but filter out sediment. When reviewing site plans, ensure that sediment controls to be used will be effective for the scale of the site.
|Insepction schedule must be no less than:|
|Every 7 days during active construction|
|Within 24 hours after a 0.5 inch rain event|
|If work is suspended due to frozen ground, inspections must begin within 24 hours after runoff occurs or construction starts|
|For parts of the site with permanent cover but work is ongoing elsewhere, inspections can be once per month|
|If the entire site has permanaent cover and there is no active construction, inspections can be once per month for twelve months|
Site inspections must be conducted by a trained person every seven days and within 24 hours of a rainfall event equal to or greater than 1/2 inch. The Construction Stormwater stormwater pollution prevention plan (SWPPP) should document the person responsible for site inspections and any modified inspection frequency.
When done correctly, dewatering activities will only discharge clear water. Therefore, when applicable, Construction Stormwater stormwater pollution prevention plans (SWPPPs) should include the following.
|BMP maintenance schedule must be no less than:|
|End of next business day for nonfunctioning BMPs|
|End of next business day or as soon as conditions allow for nonfunctioning perimeter control|
|72 hours or as soon as conditions allow for draining sedimentation basins|
|24 hours for tracked sediment|
|7 days for removing deltas and sediment from surface water and restabiliztion|
Sediment control devices are only effective if properly maintained. Ensure Construction Stormwater stormwater pollution prevention plans (SWPPPs) note the following schedules and procedures.
|Washout operations specifications:|
|Washout wastes must not contact the ground|
|Washout operations must not result in runoff|
Properly storing, handling, and disposing of chemicals and building materials protects stormwater. Construction Stormwater stormwater pollution prevention plans (SWPPPs) must include methods to prevent chemicals from coming in contact with stormwater.
For more information link here.
Final stabilization will provide long-term protection from sediment loss. Construction Stormwater stormwater pollution prevention plan (SWPPPs) must provide a final stabilzation plan.
For information on final stabilization and site closure, see the construction specifications for individual BMPs.
|Temporary sediment basin live storage:|
|If the live storage volume is calculated, it must accommodate a 2-year, 24 hour flood event, but cannot be less than 1,800 cubic ft|
|If live storage is not calculated, then the basin must accommodate 3,600 cubic ft of live storage|
Sediment basins are used for to capture stormwater runoff from the site and allow sediment to settle prior to discharge. If the site is using a temporary sediment basin, the Construction Stormwater stormwater pollution prevention plan (SWPPP) must describe the following.
|Infiltration prohibitions and limitations:|
|Infiltration is prohibited where: industrial facilities cannot infiltrate under an NPDES Industrial Stormwater permit, vehicle fueling/maintenance occurs, there is less than 3 ft between the infiltration device and bedrock/seasonably saturated soils, and high levels of contaminants will be mobilized|
|Infiltration is limited within: clay soils, 1,000 ft upgradient or 100 ft downgradient of active karsts, a Drinking Water Supply Management Area, or areas with infiltration rates of >8.3 inches/hour|
Permanent stormwater management systems, like infiltration basins, vegetated filter strips, stormwater ponds, must be designed, constructed, and maintained correctly in order to function properly. Construction Stormwater stormwater pollution prevention plans (SWPPPs) must describe these systems and design them to meet the following permit requirements.