A. Purpose: The purpose of this section is to promote, preserve and enhance the natural resources within the City and protect them from adverse effects occasioned by poorly sited development or incompatible activities by regulating land disturbing or development activities that would have an adverse and potentially irreversible impact on water quality and unique and fragile environmentally sensitive land; by minimizing conflicts and encouraging compatibility between urban growth and development and protection of water quality and natural areas; by preventing periodic local flooding by designing areas for ponding and retention of stormwater.
B. Applicability: Every applicant for a building permit, not exempted by subsection D of this section, or subdivision approval, or permit to allow land disturbing activities, must submit a stormwater management plan to the City. No building permit, subdivision approval or permit to allow land disturbing or development activities shall be issued until approval of the stormwater management plan or waiver of the approval requirement has been obtained in conformance with the provisions of this section.
C. Plan Approval: All plans shall be subject to approval by the City. The City shall consider issues of land usage, overall drainage for the City and existing stormwater facilities in approving any drainage plan. The City may reject any proposed plans if they do not meet the overall purpose of this section.
D. Exemptions: The provisions of this section do not apply to:
1. Any permit or approval by the City prior to the effective date hereof;
2. Installation of fences, signs, telephone and electric poles and other kinds of posts or poles;
3. Construction of a single-family home or a single duplex;
4. An addition to an existing building that does not require a conditional use permit and is less than ten percent (10%) of the total floor area of the existing building;
5. Construction of a detached accessory building that does not require a conditional use permit;
6. Emergency work to protect life, limb or property;
7. Land disturbing activities conducted by the City affecting less than five (5) acres.
E. Waiver: The City Council may waive any requirement of this section upon making a finding that compliance will impose an unnecessary hardship or the project does not have any significant alterations of existing stormwater conditions, and the waiver of such requirements will not adversely affect the standards and requirements of this section. The City Council may require as a condition of the waiver such dedication or construction as may be necessary to adequately meet said standards and requirements. The City Council may require as condition of the waiver that the applicant make an in kind or monetary contribution to the development and maintenance of community stormwater management activities as designated by the City Council.
F. Application: A written application signed by a licensed professional engineer in the State of Minnesota for stormwater management plan approval shall be submitted with the proposed land disturbing or development activities to the City. The application shall include a statement indicating the grounds upon which the approval is requested, a statement that the proposed use is permitted within the underlying zoning district and adequate evidence showing that the proposed use will conform to the standards set forth in this section.
G. Stormwater Management Plan: At a minimum, the stormwater management plan shall abide by the Minnesota National Pollutant Discharge Elimination System (NPDES) construction general permit, and contain the following information:
1. Site map showing the site and immediately adjacent areas, existing topography with contour intervals appropriate to the topography of the land, delineation of all streams, public waters and wetlands located on and immediately adjacent to the site, location and dimensions of existing stormwater drainage systems and natural drainage patterns on and immediately adjacent to the site showing in which direction and what rate stormwater is conveyed from the site, a description of the soils on the site, vegetative cover delineating the vegetation proposed for removal, 100-year floodplain, flood fringes, floodways and a watershed boundary map;
2. Site construction plan, including location and dimensions of all proposed land disturbing or development activities, and any phasing of those activities, locations and dimensions of all temporary soil or dirt stockpiles, locations and dimensions of all construction and erosion control measures, schedule of anticipated starting and completion date of each land disturbing or development activity, provisions for maintenance of the construction and erosion control measures during construction; geotechnical report examining groundwater versus basement floors and intended discharge of detention basins (infiltration versus piped discharge);
3. Final site conditions plan, including finished grade and contours, landscape plan, drainage plan delineating 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, proposed size, alignment and intended use of any structure to be erected on the site, delineation and tabulation of all areas which shall be paved or other impervious surfaces, including a description of the surfacing materials to be used, and any other pertinent information, which is necessary for the review of the project.
4. A written report summary discussing pre- and post-development hydrology and hydraulic analysis, erosion and sedimentation control measures to be used during and after construction, protection measures for proposed and existing structures, and water quality concerns. If structural Best Management Practices effectiveness is not as planned, the applicant/owner shall implement additional Best Management Practices to ensure postconstruction stormwater management conditions are met.
H. Site Erosion Control: The following criteria applies to construction activities that result in runoff leaving the construction site: 1) channelized turnoff from adjacent areas passing through the site shall be directed around disturbed areas, if practical; and 2) all activities on the site shall be conducted in sequence to minimize the area of bare soil exposed at one time.
I. Criteria For Permanent Facilities:
1. An applicant engaged in land disturbing or development activities shall construct all stormwater management facilities necessary to manage increased runoff so that the peak discharge rates for a 2-year, 10-year and 100-year, 24-hour event, existing before the proposed development, shall not be increased and accelerated channel erosion shall not occur as a result of the proposed land disturbing or development activities.
2. The applicant shall give consideration to reducing the need for stormwater management facilities 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.
3. The following stormwater management practices shall be investigated in the development of a stormwater management plan in the following descending order of preference:
a. Natural infiltration by use of open vegetated swales and natural depressions;
b. Flow attenuation by use of open vegetated swales and natural depressions; and
c. Stormwater detention facilities.
4. A combination of successive practices may be used to achieve the applicable minimum control requirements specified above. Justification shall be provided by the applicant for the method selected.
J. Design Standards: Stormwater detention facilities constructed in the City shall be designed according to the most current technology as reflected in the Minnesota Pollution Control Agency's Publication "Protection of Water Quality in Urban Areas", and shall contain at a minimum the following design factors:
1. A permanent pond surface area equal to two percent (2%) of the impervious area draining to the pond or one percent (1%) of the entire area draining to the pond, whichever amount is greater;
2. An average permanent pool depth of four feet to ten feet (4' - 10'), not including sediment storage;
3. A permanent pool length to width ratio of three to one (3:1) or greater;
4. A minimum protective shelf extending ten feet (10') into the permanent pool with a slope of ten to one (10:1), beyond which slopes should not exceed three to one (3:1);
5. A protective buffer strip of vegetation surrounding the permanent pool at a minimum width of one rod (16.5 feet);
6. All stormwater detention facilities shall have a device to keep oil, grease and other floatable materials from moving downstream as a result of normal operations;
7. All stormwater detention facilities must have a forebay (i.e., preliminary sedimentation basin), to remove coarse grained particles prior to discharge into a watercourse or storage basin;
8. All stormwater ponds shall be designed to account for twenty five (25) year sediment storage;
9. Retention basins shall be designed to hold a 100-year storm event back to back and maintain one foot (1') freeboard to the emergency overflow outlet;
10. Infiltration rates shall assume fifty percent (50%) clogging;
11. Design and construct stormwater management practices that manage rainfall on site, and prevent the off-site discharge of the precipitation from the first one inch (1") of runoff from the new impervious surfaces created by the project. Discharge volume reduction can be achieved by engineered infiltration, canopy interception, soil amendments, evaporation, rainfall harvesting, and/or evapotranspiration and any combination of the aforementioned practices. This first one inch (1") of rainfall must be one hundred percent (100%) managed with no discharge to surface waters.
K. Wetlands:
1. Runoff shall not be discharged directly into wetlands without presettlement of the runoff.
2. A protective buffer strip of natural vegetation at one rod (16.5 feet) in width shall surround all wetlands.
3. Wetlands must not be drained or filled, wholly or partially, unless replaced by restoring or creating wetland areas of at least equal public value as determined by the City Council.
L. Steep Slopes: No land disturbing or development activities shall be allowed on slopes of eighteen percent (18%) or more.
M. Catch Basins: All newly installed and rehabilitated catch basins that discharge to stormwater ponds or waters of the State, shall be provided with a sump area for the collection of coarse grained materials and shall be cleaned when they are half filled with material.
N. Drain Leaders: All newly constructed and reconstructed buildings shall route roof drain leaders to pervious areas wherein the runoff can be allowed to infiltrate.
O. Inspection And Maintenance: All stormwater management facilities shall be designed to minimize the need of maintenance, to provide access for maintenance purposes and to be structurally sound. All stormwater management facilities shall have a plan of operation and maintenance that assures continued effective removal of pollutants carried in stormwater management facilities. It shall be the responsibility of the applicant to obtain any necessary easement or other property interest to allow access to the stormwater management facilities for inspection and maintenance purposes. All privately owned Best Management Practices shall have a maintenance agreement with the City of Little Falls.
P. Easements And Outlots: The City may require easements or outlots which cover the stormwater infrastructure, as deemed necessary to protect the City's interest.
Q. Mitigation: In the event TSS and/or TP reduction requirements cannot be met through on-site treatment, the applicant, with City approval, can construct off site mitigation to address the required TSS and/or TP requirements.
Mitigation project areas are selected in 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 upstream;
4. Locations anywhere within the City's jurisdiction.
Mitigation projects must involve the creation of new structural stormwater Best Management Practices or the retrofit of existing structural stormwater Best Management Practices or the use of a properly designed regional structural stormwater Best Management Practice.
Routine maintenance of structural stormwater Best Management Practices already required by this permit cannot be used to meet mitigation requirements of this subsection.
Mitigation projects shall be completed within twenty four (24) months after the start of the original construction activity.
R. Approval: Stormwater management plans meeting the requirements of this section shall be submitted to the Public Works Director/City Engineer for review and compliance with the standards of this section. The Public Works Director/City Engineer shall approve, with conditions or deny the stormwater management plan. If a particular stormwater management plan involves a complex application or has the potential for significant controversy, a public hearing may be scheduled before the Planning Commission for public input.
S. Duration: Approval of any plan submitted under the provisions of this section shall expire one year after the date of approval unless construction has commenced in accordance with the plan. However, if prior to the expiration of approval, the applicant makes a written request to the Public Works Director/City Engineer for an extension of time to commence construction setting forth the reasons for the requested extension, the Public Works Director/City Engineer may grant one extension of not greater than one year. Receipt of any request for an extension shall be acknowledged by the City within fifteen (15) calendar days. The Public Works Director/City Engineer shall make a decision on the extension within thirty (30) calendar days of receipt. Any plan may be revised in the same manner as originally approved. Any denied application may be resubmitted with additional information addressing the concerns contained within the denial. The resubmitted plan is subject to all applicable fees and shall be considered a new application.
T. Conditions: A stormwater management plan may be approved subject to compliance with conditions reasonable and necessary to ensure that the requirements contained in this section 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, stage the work over time, require alteration of the site design to ensure buffering, require the acquisition of certain lands or easements, and require the conveyance to the City of Little Falls or other public entity of certain lands or interest therein. The City may specify special requirements for specific watershed within the City and its extraterritorial jurisdiction. The nature of these requirements will be subject to the unique environmental and natural resources environment of each subwatershed. Approval of a plan shall bind the applicant to perform all of the conditions and requirements of the plan prior to any land disturbing activities. A plan issued under this section runs with the land and is a condition of plat approval. Any owner or subsequent owner of any parcel within the plat must comply with the plan or any approval revision or modification of the plan.
U. Record Drawings: Upon completion of construction activities, the applicant shall submit the final stormwater management plan to document any change to the original stormwater management concept. The final plan shall contain record drawings, in paper and in electronic format (AutoCAD), sharing the final configuration of all improvements. The final plan shall be certified by the registered professional engineer in the State of Minnesota. (Ord. 96, 6th Series, eff. 9-5-2017)