(A) Construction stormwater management. Any applicant proposing a land disturbance activity within the city that is one-half acre or larger, including projects less than one-half acre that are part of a larger common plan of development or sale, shall apply to the city for a grading permit. Any applicant proposing a land disturbance activity within the city that is one acre or larger will also have to obtain coverage under the Minnesota Pollution Control Agency’s Construction Stormwater General Permit – MNR100001 (CSW permit). The applicant shall submit a grading plan and a site plan with the application. No construction activity shall begin until the site plan is approved by the city engineer and the grading permit is issued. At a minimum, the applicant’s site plan must include all items as required by the most current CSW permit, including but not limited to:
(1) Erosion prevention practices;
(2) Sediment control practices;
(3) Dewatering and basin draining;
(4) Inspection and maintenance;
(5) Pollution prevention management measures;
(6) Temporary sediment basins; and
(7) Termination condition.
(B) Post-construction stormwater management. Post-construction management applies to a land disturbance of greater than or equal to one-half acre, including projects less than one-half acre that are part of a larger common plan of development or sale. Applicants shall submit a site plan with post-construction stormwater management BMPs designed with accepted engineering practices to the city engineer for review and approval prior to any construction activity.
(1) The permittee shall use permanent structural best management practices in order to achieve the applicable minimum control requirements as specified by the most current version of the National Pollution Discharge Elimination System/State Disposal System (NPDES/SDS) Municipal Separate Storm Sewer (MS4) permit. The permanent structural BMPs must treat the water quality volume on any project where the sum of the new impervious surface and the fully reconstructed impervious surface equals one or more acres.
(a) For construction activity (excluding linear projects), the water quality volume must be calculated as one inch times the sum of the new and the fully reconstructed impervious surface.
(b) For linear projects, the water quality volume must be calculated as the larger of one inch times the new impervious surface or one-half inch times the sum of the new and the fully reconstructed impervious surface.
(2) The permittee is prohibited from using infiltration techniques to achieve the conditions in § 154.03(B)(1)(a) and (b) when the infiltration stormwater BMP will receive discharges from or be constructed in areas:
(a) That receive discharges from vehicle fueling and maintenance areas, regardless of the amount of new and fully reconstructed impervious surface;
(b) Where high levels of contaminants in soil or groundwater may be mobilized by the infiltrating stormwater. To make this determination, the owners and/or operators of construction activity must complete the MPCA’s site screening assessment checklist or conduct their own assessment. The submitted assessment must be retained with the site plans;
(c) Where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour;
(d) With less than three feet of separation distance from the bottom of the infiltration system to the elevation of the seasonally saturated soils or the top of bedrock;
(e) Of predominately Hydrologic Soil Group D (clay) soils;
(f) In an Emergency Response Area (ERA) within a Drinking Water Supply Management Area (DWSMA) as defined in Minn. Rule 4720.5100, subp. 13, classified as high or very high vulnerability as defined by the Minnesota Department of Health;
(g) In an ERA within a DWSMA classified as moderate vulnerability unless the permittee performs or approves a higher level of engineering review sufficient to provide a functioning treatment system and to prevent adverse impacts to groundwater;
(h) Outside of an ERA within a DWSMA classified as high or very high vulnerability unless the permittee perform or approves a higher level of engineering review sufficient to provide a functioning treatment system and to prevent adverse impacts to groundwater;
(i) Within 1,000 feet up-gradient or 100 feet down gradient of active karst features; or
(j) That receive stormwater runoff from these types of entities regulated under NPDES for industrial stormwater: automobile salvage yards; scrap recycling and waste recycling facilities; hazardous waste treatment, storage, or disposal facilities; or air transportation facilities that conduct deicing activities.
(3) For non-linear projects where the water quality volume cannot cost effectively be treated as required by § 154.03(B)(1)(a), on the site of the original construction activity, the owner of the construction activity shall identify locations where off-site treatment projects can be completed. If the entire water quality volume is not addressed on the site of the original construction activity, the remaining water quality volume must be addressed through off-site treatment and, at a minimum, the permittee must:
(a) Select an off-site location using the following order of preference:
1. Locations that yield benefits to the same receiving water that receives runoff from the original construction activity;
2. Locations within the same Department of Natural Resources catchment area as the original construction activity;
3. Locations in the next adjacent Department of Natural Resources catchment area up-stream; or
4. Locations anywhere within the city’s jurisdiction.
(b) Off-site treatment projects must involve the creation of new permanent structural stormwater BMPs or the retrofit of existing structural stormwater BMPs, or the use of a properly designed regional structural stormwater BMP. Routine maintenance of structural stormwater BMPs required by the MS4 permit cannot be used to meet mitigationrequirements of § 154.03(B).
(c) Off-site treatment projects must be completed no later than 24 months after the start of the original construction activity.
(4) For linear projects where the entire water quality volume cannot be treated within the existing right-of-way in accordance with § 154.03(B)(1)(b), a reasonable attempt to obtain additional right-of-way, easement, or other permission to treat the stormwater during the project planning process must be made. Volume reduction practices must be considered first. Volume reduction practices are not required if the practices cannot be provided cost effectively as approved by the city engineer. If additional right-of-way, easements, or other permission cannot be obtained, owners of construction activity must maximize the treatment of the water quality volume prior to discharge.
(5) The permittee, upon approval by the city, may elect to make a payment in lieu of a private mitigation project, as outlined in § 154.03(B)(1), as funding for a public stormwater project. The payment will be used to meet the requirements of § 154.03(B)(1)(a) and (b) utilizing the same criteria in § 154.03(B)(3)(a), (b) and (c).
(6) Long-term inspection and maintenance plans for privately-owned permanent stormwater management facilities are required. They must be submitted with the grading permit application and site plan to the city for review and approval.
(7) The owners of private stormwater structural BMPs, constructed after August 1, 2013, to meet the requirements of § 154.03(B)(1)(a) and (b), and are directly connected to the city’s MS4 are responsible for the long term operations and maintenance of the BMP. The owner shall allow the city engineer upon presentation of credentials, to access to the site at all times in accordance with the provisions of § 154.10. The city may assess the owner for maintenance costs if the owner fails to complete the required maintenance. The city may also direct the owner to modify, reconstruct or construct a new structural stormwater BMP, if the current structural BMP fails to meet the requirements of § 154.03(B)(1)(a) and (b). The city may assess the engineering and construction costs to the owner.
(Ord. 23-003, passed 3-13-2023)