(A) Application. A written application for stormwater management plan approval, along with the proposed stormwater management plan, shall be filed with the Engineering Department when applicable and shall include a statement indicating the purpose for which the approval is requested and adequate evidence showing that the proposed use will conform to the standards set forth in this subchapter.
(B) Stormwater Management Plan Submission. Drawings, plans, and reports together with information required in this section shall be submitted to the Engineering Department when applicable and shall be accompanied by all applicable fees. Paper copies shall be submitted if requested by the Engineering Department. All submissions must be received and approved prior to commence of any land disturbing activities.
(C) Stormwater management plan approval. No stormwater management plan which fails to meet the standards contained in this section shall be approved.
(D) Conditions. A stormwater management plan may be approved subject to compliance with conditions reasonable and necessary to ensure that the requirements contained in this subchapter and requirements designated by the City Engineering Department are met.
(E) Compliance with city management plans. All stormwater management plans must be prepared in accordance with the city stormwater management plan (SWMP) and the city's MS4 stormwater pollution prevention plan (SWPPP), on file in the Office of the City Engineer, as revised from time.
(F) Compliance with watershed management plans/groundwater management plans/source water protection. Stormwater management plans shall be consistent with adopted watershed management plans and groundwater management plans prepared in accordance with Minn. Statutes §§ 103B.231 and 103B.255 respectively, and as approved by the Minnesota Board of Water and Soil Resources and Minnesota Department of Health in accordance with state law.
(G) Engineering design checklist and standards. All stormwater management plans must be prepared and conducted in accordance with the Engineering Department design checklist and standards for stormwater design, on file in the Office of the City Engineer, as revised from time to time. At a minimum the following information is required to be contained in all stormwater management plans:
(1) Proper identification of owner(s) and contractor(s);
(2) Description of construction activity;
(3) Existing site conditions;
(4) Site construction plan;
(5) Erosion and sediment control BMP's;
(6) Drainage and grading;
(7) Plan of final site conditions;
(8) Post construction stormwater management;
(9) Plan for long-term stormwater management including annual maintenance plans and recorded agreements; and
(10) Models, methods, and calculations for site hydrology and hydraulics including discharge rates, volume, and quality.
(H) Stormwater pollution prevention plan. All stormwater management plans must be accompanied by a Stormwater Pollution Prevention Plan (SWPPP) and all land disturbing activities shall be conducted in accordance with the most recent Minnesota Pollution Control Agency (MPCA) General NPDES/SDS Construction Permit MN R100001 (CGP) and are subject to § 52.31.
(I) Easements. If a stormwater management plan involves direction of some or all runoff, off the site, it shall be the responsibility of the owner to obtain from adjacent property owner(s) any necessary easements or other property interests concerning flowage of water.
(J) Post construction stormwater management.
(1) Design and calculations. Site design and calculations shall be based on the following;
(a) All plans, whenever possible, shall be designed using the better site design techniques and other pertinent information found in the most recent Minnesota Stormwater Manual, which is available from the Minnesota Pollution Control Agency (MPCA) website at https://stormwater.pca.state.mn.us/.
(b) Discharge rates derived using the standard methods of the natural resource conservation service as defined in the current Hydrology Guide for Minnesota, HydroCAD, or other hydrologic/ hydraulic models included in the Minnesota Stormwater Manual and subject to approval of the City Engineer.
(c) All calculations shall be made using National Oceanic and Atmospheric Administration Atlas 14.
(d) All calculations and methods used to determine water quality and volume treatment and/or control shall be determined by a licensed engineer and is subject to approval by the City Engineer.
(2) Rate control. Any land disturbing or development activity that results in one or more acres of land disturbances must meet the following;
(a) All stormwater management facilities necessary to manage increased runoff so that the two-year, ten-year, and 100-year 24 hour storm peak discharge rates existing before the proposed development shall not be increased unless otherwise approved by the City Engineer. Applicant shall also verify accelerated channel erosion will not occur as a result of the proposed land disturbing or development activity.
(b) The applicant shall give highest preference to reducing the need for stormwater management facilities by incorporating the use of natural topography and green infrastructure.
(3) Water quality and volume control. For the proposed land disturbing and development activity, all permanent structural best management practices (BMPs) shall be installed in order to achieve the applicable minimum control requirements as specified by the most current version of the NPDES/SDS municipal separate storm sewer system permit. The applicant shall use any combination of BMPs, with the highest preference given to green infrastructure techniques and practices necessary to meet the following conditions in divisions (J)(3)(a) through (c) below to the maximum extent practicable (MEP);
(a) Any project where the sum of the new impervious surfaces and the fully reconstructed surfaces equals one or more acres shall provide treatment for the calculated water quality volume.
(b) For non-linear projects, water quality volume must be calculated as one inch times the sum of the new and the fully reconstructed surfaces.
(c) For linear projects the water quality volume must be calculated as the larger of one inch times and the new impervious surface or one-half inch times the sum of the new and fully reconstructed impervious surfaces.
(d) The minimum impervious area draining to BMPs providing required water quality volume shall be equal to the sum of new and fully reconstructed surfaces or to the maximum extent practicable as determined by the City Engineer.
(e) Projects adding new impervious surfaces and/or fully reconstructed surfaces will be considered in cumulative over the life of the property. Land disturbance activity applicable to this requirement will be determined with respect to all development or redevelopment that has occured from the time of adoption.
(K) Limitations and restrictions. The use of infiltration techniques are prohibited when the infiltration structural BMP will be constructed in the following areas;
(1) Where industrial facilities are not authorized to infiltrate industrial stormwater under an NPDES/SDS industrial stormwater permit.
(2) Where vehicle fueling and maintenance occurs.
(3) With less than three feet of separation distance from the bottom of the infiltration system to the elevation of seasonally saturated soils or the top of bedrock.
(4) Where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating stormwater.
(a) The use of infiltration techniques will be restricted, but may be permitted if higher engineering review/testing ensures the practice will perform properly, when the infiltration structural BMP will be constructed in the following areas;
1. With predominately Hydrologic Soil Group D soils.
2. Within 1,000 feet up-gradient, or 100 feet down-gradient of active karst features.
3. Within a Drinking Water Supply Management Area (DWSMA) as defined in Minn. Rules 4720.5100, Subp.13.
4. Where soil infiltration rates are more than 8.3 inches per hour.
(L) Mitigation provisions for linear projects. If the owner believes that the entire water quality volume requirements cannot be met on the site of the original construction activity, the owner must provide adequate documentation to the city as support including attempts to acquire additional right-of-way or other permission to provide treatment for the full water quality volume. The owner must provide treatment for the water quality volume to the maximum extent practicable. No further off-site mitigation is required.
(1) The owner of the construction activity is precluded from infiltrating stormwater through a design system limitation described in division (K) of this section; and
(2) The owner of the construction activity implements to maximum extent practicable, volume reduction techniques, other than infiltration, on the site of the original construction activity that reduces stormwater discharge volume, but may not meet the requirements of post-construction stormwater management.
(M) Mitigation provisions. If the owner believes that the water quality volume requirements cannot be met on the site of the original construction activity, the owner must provide adequate documentation to the city as support. Stormwater discharges that do not meet the water quality volume on the site of the original construction activity must be met through mitigation. At the city's discretion, off-site mitigation may be allowed. The owner must identify locations where mitigation projects can be completed. The proposed mitigation must meet the following;
(1) Mitigation project areas must be selected in the following order of preference, in consultation and with approval by the city;
(a) Locations yielding benefits to the same receiving water that receives runoff from the original construction activity.
(b) Locations within the same Department of Natural Resource (DNR) catchment area as the original construction activity.
(c) Locations in the next adjacent DNR catchment up-stream.
(d) Locations anywhere within the city's jurisdiction.
(2) Mitigation projects must involve the creation of new structural stormwater BMP’s, the retrofit of existing structural stormwater BMP’s, or the use of properly designed regional structural stormwater BMP’s.
(3) Routine maintenance of existing structural stormwater BMP's is required and cannot be used to meet mitigation requirements of this section.
(4) Mitigation projects must be completed within 24 months after the start of the original construction activity.
(5) If the mitigation project is a private structural BMP and the city is not responsible for long-term maintenance of the project, the city will require written and recorded documentation of responsibility for maintenance.
(6) Payment in lieu of private mitigation projects, subject to city approval, may be accepted and used for funding a public stormwater project. The payment will be used to meet the water quality volume requirements outlined in divisions (J) and (M) of this section.
(Ord. 1519, passed 3-3-2015; Ord. 1638, passed 9-20-2022)