(A) Approval procedures.
(1) Application. A written application for stormwater management plan approval, along with a proposed stormwater management plan and maintenance agreement, shall be filed with the Engineering Division of the Operations and Maintenance Department. The application shall include a statement indicating the grounds upon which the approval is being requested, that the proposed use is permitted by right or as an exception in the underlying zoning district, and adequate evidence showing that the proposed use will conform to the standards set forth in this chapter and the City Code.
(2) Required plan submittals.
(a) Two sets of clearly legible blue or black lined copies of drawings, electronic copy of drawings, and required information shall be submitted to the Engineering Division of the Public Works Department along with the process and approval fee. The plans shall be drawn at a minimum scale of one inch equals 100 feet and shall contain the following information:
1. Existing site map. A map of existing conditions showing the site and immediately adjacent areas within 200 feet of the site, including:
a. The name and address of the applicant, the section, township and range, north point, date and scale of drawing and number of sheets.
b. The location of the property by showing an insert map at a scale sufficient to clearly identify its location and giving such information as the name and numbers of adjoining roads, railroads, utilities, subdivisions, cities, townships and districts or other landmarks.
c. The existing topography with a contour interval appropriate to the topography of the land but in no case having a contour interval greater than two feet.
d. A delineation of all ponds, infiltration features, streams, rivers, public waters and wetlands located on and immediately adjacent to the site, including the depth of the water, the normal water level (NWL), the 100-year high water level (HWL), the ordinary high water level (OHW), a description of all vegetation which may be found in the water, a statement of general water quality and any classification given to the water body or wetland by the Minnesota Department of Natural Resources (MnDNR), the MPCA or the United States Army Corps of Engineers (USACE).
e. The location and dimensions of existing stormwater drainage systems and natural drainage patterns on and immediately adjacent to the site delineating in which direction and at what rate stormwater is conveyed from the site, identifying the receiving stream, river, public water, or wetland, and setting forth those areas of the unaltered site where stormwater collects.
f. A description of the soils of the site, including a map indicating soil types of areas to be disturbed as well as a soil report containing information on the suitability of the soils for the type of storm water system proposed and describing any remedial steps to be taken by the applicant to render the soils suitable.
g. The location and description of any vegetative cover and a clear delineation of any vegetation proposed for removal.
h. The location of 100-year floodplains, flood fringes and floodways.
i. The locations of any existing overhead or underground utilities.
j. The locations of property lines and easements.
k. A city approved benchmark listing location and elevation.
(3) Site construction plan. A site construction plan including:
(a) Locations and dimensions of all proposed land disturbing activities and any phasing of those activities.
(b) Total site area.
(c) Total area disturbed.
(d) Locations and dimensions of all temporary soil or dirt stockpiles.
(e) Locations and dimensions of all construction site erosion control measures necessary to meet the requirements of this chapter. A schedule of the anticipated start and completion date of each land disturbing activity including the installation of construction site erosion control measures needed to meet the requirements of this chapter.
(f) Provisions for maintenance of the construction site erosion control measures during construction.
(4) Plan of final site conditions. A plan of final site conditions on the same scale as the existing site map showing the proposed site changes, including:
(a) Finished grading shown at contours at the same interval as provided above or as required to clearly indicate the relationship of proposed changes to existing topography and remaining features.
(b) A landscape plan, drawn to an appropriate scale, including dimensions and distances and the location, type, size and description of all proposed landscape materials which will be added to the site as part of the development.
(c) A drainage plan of the developed site delineating in which direction and at what rate stormwater will be conveyed from the site and setting forth the areas of the site where stormwater will be allowed to collect.
(d) The proposed size, alignment and intended use of any structures to be erected on the site.
(e) A clear delineation and tabulation of all areas which will be paved or surfaced, including a description of the surfacing material to be used.
(f) Any other information pertinent to the particular project which, in the opinion of the applicant or the Engineering Department, is necessary for the review of the project.
(g) Proposed normal water level (NWL), 100-year high water level (HWL), ordinary high water level (OHW) of any ponds, infiltration facilities, streams, rivers, public waters, or wetlands on or downstream from the site.
(h) Building elevations including low floor elevations and low building opening elevations.
(i) Overland emergency overflow routes and their elevations.
(5) Stormwater calculations. Calculations demonstrating the following data shall be provided, according to the method established by the Engineering Department:
(a) Drainage maps that show the site, land that drains onto the site, and land that the site drains onto for existing and proposed conditions. Delineated drainage areas for ponds, wetlands, or other relevant waters should be indicated on these maps.
(b) A stormwater model conforming to Engineering Department standards that includes drainage areas, cover types, pond and wetland sizes, pond and wetland outlets, and natural or piped conveyance systems.
(c) Peak runoff rates from the site before and after development demonstrating that the proposed conditions conform to the policies outlined in the city's Local Water Management Plan and this chapter's design criteria.
(d) Volume of runoff from the site before and after development.
(e) National Urban Runoff Program ("NURP") volume below the normal outlet required and provided in each pond.
(f) Infiltration calculations for proposed conditions.
(g) A narrative summarizing the calculations and demonstrating that proposed drainage alterations do not unreasonably burden upstream or downstream land.
(h) Soil borings, if requested by the Engineering Department.
(6) Maintenance agreement. The applicant shall enter into a maintenance agreement with the city that documents all responsibilities for operation and maintenance of long-term stormwater treatment practices. Such responsibility shall be documented in a maintenance plan and executed through a maintenance agreement. All maintenance agreements must be approved by the city and recorded at the Hennepin County recorder's office prior to final plan approval. At a minimum, the maintenance agreement shall describe the following inspection and maintenance obligations:
(a) The responsible party who is permanently responsible for maintenance of the structural and nonstructural measures.
(b) Pass responsibilities for such maintenance to successors in title.
(c) Allow the city and its representatives the right- of-entry for the purposes of inspecting all permanent stormwater management systems.
(d) Allow the city the right to repair and maintain the facility, if necessary maintenance is not performed after proper and reasonable notice to the responsible party of the permanent stormwater management system.
(e) Include a maintenance plan that contains, but is not limited to the following:
1. Identification of all structural permanent stormwater management systems.
2. A schedule for regular inspections, monitoring, and maintenance for each practice. Monitoring shall verify whether the practice is functioning as designed and may include, but is not limited to quality, temperature, and quantity of runoff.
3. Identification of the responsible party for conducting the inspection, monitoring and maintenance for each practice.
4. Include a schedule and format for reporting compliance with the maintenance agreement to the city.
(f) The issuance of a permit constitutes a right-of-entry for the community or city, its contractors, and agents to enter upon the construction site. The applicant shall allow the community city, its contractors, agents and any their authorized representatives, upon presentation of credentials, to:
1. Enter upon the permitted site for the purpose of obtaining information, examination of records, conducting investigations or surveys.
2. Bring such equipment upon the permitted development as is necessary to conduct such surveys and investigations.
3. Examine and copy any books, papers, records, or memoranda pertaining to activities or records required to be kept under the terms and conditions of the permit.
4. Inspect the stormwater pollution control measures.
5. Sample and monitor any items or activities pertaining to stormwater pollution control measures.
6. Correct deficiencies in stormwater and erosion and sediment control measures.
(B) Stormwater management plan review procedure.
(1) Process. Stormwater management plans and maintenance agreements meeting the requirements of this chapter shall be submitted to the Engineering Department for review and approval. The Engineering Division shall recommend approval, approval with conditions, or denial of the stormwater management plan and maintenance agreement to the Planning Commission. Following Planning Commission review, the stormwater management plan and maintenance agreement shall be submitted to the City Council for its review along with the Planning Commission's recommendation.
(2) Duration. Approval of a stormwater management plan and maintenance agreement submitted under the provisions of this chapter shall expire two years after the date of approval by the City Council unless construction has commenced in accordance with the plan. However, if prior to the expiration of the approval, the applicant makes a written request to the Engineering Department for an extension of time to commence construction setting forth the reasons for the requested extension, the City Council may grant one extension of not greater than one single year.
(3) Revisions. A stormwater management plan and maintenance agreement may be revised. All revised plans must contain all information required by this chapter and must be reviewed and approved by the Engineering Department.
(4) Conditions. A stormwater management plan and maintenance agreement may be approved by the City Council subject to compliance with conditions that are necessary to ensure that the requirements contained in this chapter are met. Such conditions may, among other matters, limit the size, kind or character of the proposed development; require the construction of structures, drainage facilities, storage basins and other facilities; require replacement of vegetation; establish required monitoring procedures; require that the work be staged over time; require alteration of the site's design to ensure buffering; or require the conveyance to the city or other public entity of certain lands or interests therein.
(5) Agreement. Upon approval of the stormwater management plan and maintenance agreement by the City Council, the applicant shall enter into an agreement with the city to ensure that any required improvements are constructed, any required easements are granted or dedicated and that there is compliance with any conditions imposed by the City Council. The agreement shall guarantee completion and compliance with the conditions within a specific time, which time may be extended by the City Council. The agreement shall be in a form acceptable to the city.
(6) Financial guarantee. Upon approval of the stormwater management plan and maintenance agreement by the City Council, the applicant shall submit a letter of credit, or cash escrow, to cover 125% of the amount of the established cost of complying with the stormwater management plan. This financial guarantee shall be in a form acceptable to the city and may be incorporated into the financial guarantee provided for grading activities and/or the financial guarantee provided for street and utility activities.
(7) Fees. All applications for stormwater management plan and maintenance agreement approval shall be accompanied by a processing and approval fee as set by the most recent edition of the city's adopted Fee Schedule.
(C) Stormwater management plan approval and implementation standards.
(1) Compliance with standards. No stormwater management plan which fails to meet the standards contained in this section shall be approved by the City Council.
(2) All stormwater management plans must be submitted to the City Engineer prior to the start of construction activity. At a minimum all applicants shall meet the criteria set forth below and observe the standards established in NPDES Construction Stormwater General Permit requirements.
(3) The city adopts the MPCA's Minnesota Stormwater Manual as its stormwater runoff design standards.
(4) All stormwater management plans must address erosion and sediment control requirements of this chapter.
(5) Stormwater management requirements for permanent facilities.
(a) An applicant shall install or construct, on or for the proposed land disturbing or development activity, all stormwater management facilities necessary to meet the criteria of the NPDES Construction Stormwater General Permit. No private stormwater facilities will be approved by the city unless a maintenance agreement and maintenance plan are provided that defines who will conduct the maintenance, the type of maintenance and intervals of the maintenance to be performed. In the alternative, or in partial fulfillment of this requirement and upon approval of the Engineering Department, an applicant may make an in-kind or monetary contribution to the development and maintenance of regional stormwater management facilities designed to serve multiple land disturbing and development activities undertaken by one or more persons, including the applicant.
(b) Proposed stormwater management plans shall incorporate volume control, water quality control, and rate control as the basis for stormwater management in the proposed development plan on sites without restrictions. All proposed projects shall be in conformance with the most current requirements of the MPCA's Municipal Separate Storm Sewer Systems (MS4) Permit and the Shingle Creek and West Mississippi Watershed Management Commissions, as applicable.
1. Volume control.
a. New development projects less than one acre in size.
i. The applicant shall provide a detailed plan and/or narrative describing the BMPs that will be incorporated in the development to reduce runoff volume and improve water quality.
ii. There shall be no net increase from pre-project conditions (on an annual average basis) of:
1) Stormwater discharge volume, unless precluded by the stormwater management limitations as defined by the MPCA's MS4 Permit.
2) Stormwater discharges of total suspended solids (TSS).
3) Stormwater discharges of total phosphorus (TP).
b. New development. For new, nonlinear developments, stormwater runoff volume abstraction via infiltration will be controlled and the post-construction runoff volume shall be retained on site for 1.0 inches of runoff from all impervious surfaces on the site that result in a net increase of impervious of one acre or greater. If filtration of the water quality volume is deemed necessary through alternative compliance sequencing, the required stormwater runoff volume shall be multiplied by 1.82 (i.e. 55% filtration credit) and the filtration BMP shall provide this storage volume below the invert of the low overflow outlet of the BMP (perforated drain pipes for filtration will not be considered the low overflow outlet).
c. Redevelopment. For redevelopment projects, stormwater runoff volume abstraction via infiltration will be controlled and the post-construction runoff volume shall be retained on site for 1.0 inches of runoff from the new impervious surfaces created by the project. If filtration of the water quality volume is deemed necessary through alternative compliance sequencing, the required stormwater runoff volume shall be multiplied by 1.82 (i.e. 55% filtration credit) and the filtration BMP shall provide this storage volume below the invert of the low overflow outlet of the BMP (perforated drain pipes for filtration will not be considered the low overflow outlet). There shall be a net reduction from pre-project conditions (on an annual average basis) of:
i. Stormwater discharge volume, unless precluded by the stormwater management limitations as defined by the MPCA's MS4 permit.
ii. Stormwater discharges of TSS.
iii. Stormwater discharges of TP.
d. Linear projects. 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. Where the entire water quality volume cannot be treated within the existing right-of-way, 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 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 from the MS4.
2. Water quality control. The water quality requirement is met if the project meets the volume control requirement outlined in § 153.07(C)(5)(b)1.
a. Where infiltration is not advisable or infeasible due to site conditions, biofiltration must be provided for that part of the abstraction volume that is not abstracted by other BMPs. Where biofiltration is infeasible, at a minimum filtration through a medium that incorporates organic material, iron fillings, or other material to reduce soluble phosphorus must be provided.
b. There shall be no net increase in total phosphorus (TP) or total suspended solids (TSS) from pre-development land cover to post-development land cover. Pre-development land cover is defined as the predominant land cover over the previous ten years.
i. Full abstraction of 1.1 inches of runoff from all impervious surfaces will satisfy the water quality requirement.
ii. If it is not feasible to achieve the full 1.1-inch abstraction requirement, a combination of BMPs may be used to achieve the no-net-increase requirement using a water quality calculation method as outlined in the Minnesota Stormwater Manual.
iii. If permanent sedimentation and water quality ponds are used, they shall be designed to the standards set forth in the Minnesota Stormwater Manual.
iv. Runoff may be directed to a downstream facility within the same hydrologic subwatershed that has sufficient capacity to provide the required treatment. This means that no treatment may be required for an individual development provided there is a regional facility designed and constructed to accommodate the flow from this property
3. Rate control. Rate control measures are required on new development and redevelopment projects to meet this chapter's design criteria, the Minnesota Stormwater Manual and Shingle Creek and West Mississippi River Watershed Management Commissions requirements.
(c) The applicant shall reduce the need for stormwater treatment practices by incorporating the use of natural topography and land cover such as wetlands, ponds, natural swales and depressions as they exist before development to the degree that they can accommodate the additional flow of water without compromising the integrity or quality of the wetland or pond.
(d) The following stormwater management practices shall be investigated by the applicant in developing a stormwater management plan in the following descending order of preference, and the results of that investigation shall be provided to the city in written form as a part of the application:
1. Natural infiltration of precipitation on-site.
2. Flow attenuation by use of open vegetated swales and natural depressions.
3. Green infrastructure by use of rain gardens, bioswales, constructed wetlands, and other constructed infiltration practices.
4. Stormwater retention facilities.
5. Stormwater detention facilities.
(e) A combination of stormwater treatment practices may be used to achieve the applicable minimum control requirements specified in the subsection above. Justification shall be provided by the applicant for the method selected.
(f) Pond design standards. Stormwater detention facilities constructed in the city shall be designed according to standards established by the Engineering Division of the Operations and Maintenance Department, and shall contain, at a minimum, the following design factors:
1. A permanent pool ("dead storage") volume below the principal spillway (normal outlet) which shall be greater than or equal to the runoff from a 2.5-inch, 24-hour storm over the entire contributing drainage area assuming full development.
2. A permanent pool average depth (basin volume/basin area) of four to ten feet.
3. An emergency overflow (emergency outlet) adequate to control the 100-year frequency critical duration rainfall event.
4. Basin side slopes below the 100-year high water level should be no steeper than 4:1, and preferably flatter. A basin shelf with a minimum width of ten feet and one foot deep below the normal water level is recommended to enhance wildlife habitat, reduce potential safety hazards, and improve access for long-term maintenance.
5. To prevent short-circuiting, the distance between major inlets and the normal outlet shall be maximized.
6. A flood pool ("live storage") volume above the principal outlet spillway shall be adequate so that the peak discharge rate from the 1-, 10- and 100-year frequency critical duration storm is not greater than the peak discharge for a similar storm and predevelopment watershed conditions.
7. Effective energy dissipation devices which reduce outlet velocities to four feet per second or less shall consist of riprap, stilling pools or other such measures to prevent erosion at all storm water outfalls into the basin and at the detention basin outlet.
8. Consideration for aesthetics and wildlife habitat should be included in the design of the pond.
9. A skimming device must be provided to deter floatable pollutants from discharging out of pond.
10. Pond NWL elevations shall be established above the OHW of adjacent MnDNR water bodies, except where topography of the site, floodplain mitigation activities, or other design considerations are determined to be unfavorable for these conditions to occur. This determination shall be performed by an engineer, provided by the applicant, and approved by the Engineering Division of the Operations and Maintenance Department.
11. All constructed ponds shall have a maintenance access bench sufficient to provide access to all inlets and outlets. The maintenance bench shall be located within a designated outlot or within a permanent easement. The maintenance bench shall extend from the outlet elevation to one foot above the outlet elevation and its cross slope shall be no steeper than 10:1. The maintenance bench shall connect to the maintenance access.
12. All constructed ponds shall be provided a maintenance access from an adjacent roadway. The maintenance access shall be provided in the form of an easement no narrower than 20 feet. The maintenance access shall have a longitudinal slope no steeper than 6:1 and minimal cross slope. Maintenance access routes, due to their extra width, also serve well as emergency overflow (EOF) routes.
(g) Infiltration requirements. BMPs will be required to the maximum extent practical as determined by the Engineering Division of the Operations and Maintenance Department or its designee.
1. Maximum extent practical shall be the infiltration of runoff from the 100-year, 24-hour rainfall event within 48 hours. The maximum extent practical may be less than this if the Engineering Division of the Operations and Maintenance Department determines that one or more of the following conditions apply:
(a) Infiltration characteristics of soils on site are not favorable for infiltration of stormwater.
(b) The site's drainage course is to regional infiltration or detention facilities controlled by the city that reduce runoff volumes.
(c) When the site's impervious areas are not increased due to development.
(d) Other site conditions that make infiltration of stormwater impractical on the site as determined by the Engineering Division of the Operations and Maintenance Department.
(e) If one or more of these conditions apply, the Engineering Division of the Public Works Department shall quantify infiltration that will be deemed as the maximum extent practical for the site.
2. Infiltration will be prohibited where the infiltration BMP will be constructed in any of the following areas:
a. Where documented past, present, or anticipated future land uses have resulted in or may result in contamination coming in contact with stormwater runoff.
b. 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.
c. Where vehicle fueling and maintenance occur.
d. Where industrial facilities are not authorized to infiltrate industrial stormwater under and NPDES/SDS Industrial Stormwater Permit issued by the MPCA.
3. Infiltration will be restricted and subject to additional city review where the infiltration BMP will be constructed in any of the following areas:
a. Within 1,000 feet up-gradient, or 100 feet down-gradient of active karst features.
b. Where drinking water supply management areas are present, as defined by Minn. Rules 4720.51000, subp.13, unless precluded by a local unit of government with an MS4 permit.
c. Soils are predominately Hydrologic Soil Group D (clay) soils.
d. 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.
4. Stormwater runoff shall be treated in a stormwater pond or by other means prior to entering an infiltration facility.
5. The minimum infiltration requirements for any region of the city will be the requirements of the Shingle Creek and West Mississippi River Watershed Management Commissions' policies that govern that region. Shingle Creek and West Mississippi River Watershed Management Commissions' standards may be met through the use of regional or downstream systems prior to discharge of runoff to waters of the state.
6. Infiltration systems must not be excavated to final grade until the contributing drainage area has been constructed and fully stabilized. When the infiltration feature is excavated to final grade, rigorous erosion prevention and sediment control BMPs must be implemented to keep sediment and runoff completely away from the infiltration area.
7. To prevent clogging of the infiltration system, a pretreatment device must be used to settle particles before the stormwater discharges into the infiltrations system.
8. Per the stormwater management requirements for permanent facilities section of this chapter, the infiltration system must provide a water quality volume (calculated as an instantaneous volume) of one inch of runoff (or one inch minus the volume of stormwater treated by another system on the site) from the new impervious surfaces created by the project.
9. The applicant must ensure filtration systems with less than three feet of separation from seasonally saturated soils or from bedrock are constructed with an impermeable liner.
10. A minimum maintenance access of 12 feet is required.
(h) Mitigation.
1. Where construction projects cannot meet the TSS and/or TP reduction requirements for new or development projects on the site of original construction, all methods must be exhausted prior to considering alternative locations where TSS and TP treatment standards can be achieved. If the City has determined that all methods have been exhausted, the permittee will be required to identify alternative locations where TSS and TP treatment standards can be achieved. Mitigation projects will be chosen in the following order of preference:
a. Locations that yield benefits to the same receiving water that receives runoff from the original construction activity.
b. Locations within the same MnDNR catchment area as the original construction activity.
c. Locations in the next adjacent MnDNR catchment area up-stream.
d. Locations anywhere within the City of Brooklyn Park.
2. In addition, mitigation projects must also meet the following criteria:
a. Mitigation projects shall involve the establishment new structural stormwater BMPs or the retrofit of existing structural stormwater BMPs, or the use of a properly designed regional structural stormwater BMP.
b. Previously required routine maintenance of structural stormwater BMPs cannot be considered mitigation.
c. Mitigation projects must be finished within 24 months after the original construction activity begins.
d. A maintenance agreement specifying the responsible party for long-term maintenance shall be identified.
(i) Stormwater and infiltration facilities must be located at least 50 feet away from the top of bluff.
(j) Watershed management plans/groundwater management plans. Stormwater management plans shall be consistent with the Shingle Creek and West Mississippi River Watershed Management Commissions requirements and groundwater management plans prepared in accordance with Minnesota Board of Water and Soil Resources in accordance with state law.
(k) Easement. If the stormwater management plan involves direction of some or all runoff off of the site, it shall be the responsibility of the applicant to obtain from adjacent property owners any necessary easements or other property interests to permit the flow of water across the property.
(l) Low floor/building opening elevations.
1. Any new development or redevelopment shall maintain a minimum building opening elevation of at least three feet above the anticipated 100-year high water elevation as a standard practice. However, if the applicant demonstrates that this requirement would be a hardship, the standard may be reduced to two feet if all of the following can be demonstrated:
a. That, within the two-foot freeboard area, stormwater storage is available which is equal to or exceeds 50% of the storm water storage currently available in the basin below the 100-year elevation.
b. That a 25% obstruction of the basin outlet over a 24-hour period would not result in more than one foot of additional bounce in the basin.
c. That an adequate overflow route from the basin is available that will provide one foot of freeboard for the proposed low building opening.
2. Basement floor elevations must be set to an elevation that meets all of the following criteria:
a. The lowest floor elevation must be at least four feet above the currently observed groundwater elevations in the area.
b. The lowest floor elevation must be at least two feet above the elevation of any known historic high groundwater elevations for the area. Information on historic high groundwater elevations can be derived from any reasonable sources including piezometer data, soil boring data, percolation testing logs, etc.
c. The lowest floor elevation must be at least two feet above the 100-year high surface water elevation for the area unless it can be demonstrated that this standard creates a hardship. If the two-foot standard is determined by the City Council to constitute a hardship, the standard shall be at least one foot above the highest anticipated groundwater elevation resulting from a 100-year critical duration rainfall event. The impact of high surface water elevations on groundwater elevations in the vicinity of the structure should take into consideration the site's distance from the floodplain area, the soils, the normal water elevation of surface depressions in the area, the static groundwater table and historic water elevations in the area. This information shall be provided by a registered engineer or soil scientist.
(m) Impervious surface coverage of each lot must not exceed the impervious surface coverage allowed under the Zoning Ordinance.
(n) Storm sewers shall be designed to accommodate discharge rates associated with a 10-year, 24-hour rainfall event.
(Ord. 2017-1217, passed 7-10-17; Am. Ord. 2024-1304, passed 7-29-24)