(A) Generally. Every applicant for a building permit, subdivision approval, or a permit to allow land disturbing activities must submit a storm water pollution control plan to the City Engineer. No building permit, subdivision approval, or permit to allow land disturbing activities shall be issued until the city approves this plan. At a minimum these pollution abatement control practices must conform to those in the current version of the Minnesota Pollution Control Agency’s publication, Protecting Water Quality in Urban Areas.
(B) General policy on storm water runoff rates. For rivers and strains storm water discharge rates must not increase over the pre-development two-year, ten-year and 100-year peak storm discharge rates, based on the last ten years of how that land was used. Also accelerated channel erosion must not occur as a result of the proposed activity. For wetlands volume control is generally more important.
(C) The storm water pollution control plan and the grading plan. The storm water pollution control plan’s measures, the limit of disturbed surface and the location of buffer areas shall be marked on the approved grading plan, and identified with flags, stakes, signs and the like on the development site before work begins.
(D) Inspections of the storm water pollution control plan measures. At a minimum such inspections shall be done weekly and after every storm event that is large enough to result in run off from the site by either the city, developer or the developer’s designated representative
(E) Minimum requirements of the storm water pollution control plan.
(1) The name and address of the applicant and the location of the activity.
(2) Project description: the nature and purpose of the land disturbing activity and the amount of grading, utilities, and building construction involved.
(3) Phasing of construction: time frames and schedules for the project’s various aspects.
(4) A map of the existing site conditions: existing topography, property information, steep slopes, existing drainage systems/patterns, type of soils, waterways, wetlands, vegetative cover, 100-year flood plain boundaries, locations of existing and future buffer strips and labeling the portions of the site that are within trout stream or outstanding resource value water watersheds.
(5) A site construction plan that includes the location of the proposed land disturbing activities, stockpile locations, erosion and sediment control plan, construction schedule, and the plan for the maintenance and inspections of the storm water pollution control measures.
(6) Adjacent areas: neighboring streams, lakes, residential areas, roads, and the like, which might be affected by the land disturbing activity.
(7) Designate the site’s areas that have the potential for serious erosion problems.
(8) Erosion and sediment control measures: the methods that will be used to control erosion and sedimentation on the site, both during and after the construction process.
(9) Permanent stabilization: how the site will be stabilized after construction is completed, including specifications, time frames or schedules.
(10) Calculations: any that were made for the design of such items as sediment basins, wet detention basins, diversions, waterways, infiltration zones and other applicable practices.
(F) General storm water pollution control plan criteria. The plan shall address the following:
(1) Stabilizing all exposed soils and soil stockpiles and the related time frame or schedule.
(2) Establishing permanent vegetation and the related time frame or schedule.
(3) Preventing sediment damage to adjacent properties and other designated areas such as streams, wetlands, lakes and unique vegetation (such as oak groves, rare and endangered species habitats.)
(4) Scheduling for erosion and sediment control practices.
(5) Where permanent and temporary sedimentation basins will be located.
(6) Engineering the construction and stabilization of steep slopes.
(7) Measures for controlling the quality and quantity of storm water leaving a site.
(8) Stabilizing all waterways and outlets.
(9) Protecting storm sewers from the entrance of sediment.
(10) What precautions will be taken to contain sediment when working in or crossing water bodies.
(11) Restabilizing utility construction areas as soon as possible.
(12) Protecting paved roads from sediment and mud brought in from access routes.
(13) Disposing of temporary erosion and sediment control measures.
(14) How the temporary and permanent erosion and sediment control practices will be maintained.
(15) How collected sediment and floating debris will be disposed of.
(G) Minimum storm water pollution control measures and related inspections. These minimum control measures are required where bare soil is exposed. Due to the diversity of individual construction sites, each site will be individually evaluated. Where additional control measures are needed, they will be specified at the discretion of the City Engineer. The city will determine what action is necessary to prevent excessive erosion from occurring on the site.
(1) All grading plans and building site surveys must be reviewed by the city for effectiveness of erosion control measures in the context of the site topography and drainage.
(2) Sediment control measures must be properly installed by the builder before construction activity begins. Such structures may be adjusted during dry weather to accommodate short term activities, such as those that require the passage of very large vehicles. As soon as this activity is finished or before rainfall, the erosion and sediment control structures must be returned to the configuration specified by the city. A sediment control inspection must then be scheduled, and passed before a footing inspection will be done.
(3) Diversion of channeled runoff around disturbed areas, if practical, or the protection of the channel.
(4) If a storm water management plan involves directing some or all of the site’s runoff, the applicant or his or her designated representative shall obtain from adjacent property owners any necessary easements or other property interests concerning the flowing of such water.
(5) The scheduling of the site’s activities to lessen their impact on erosion and sediment creation, so as to minimize the amount of exposed soil.
(6) Control runoff as follows (Either (a) and (b) or (a) and (c)):
(a) Unless precluded by moderate or heavy snow cover (mulching can take place if a light snow cover is present), stabilize all exposed inactive disturbed soil areas within 100 feet of any water of the state, or with in 100 feet any conveyance (curb, gutter, storm sewer inlet, drainage ditch, and the like) to a water of the state with sod, seed or weed free mulch. This must be done, if the developer will not work the area for seven days on slopes greater than three feet horizontal to one foot vertical (3:1), 14 days on slopes ranging from 3:1 to 10:1 and 21 days for flatter slopes.
(b) For disturbed areas greater than five acres construct temporary or permanent sedimentation basins. Sedimentation basins must have a minimum surface area equal to at least 1% of the area draining to basin, and be constructed in accordance with accepted design specifications including access for operations and maintenance. Basin discharge rates must also be controlled to prevent erosion in the discharge channel. (The applicant is required to obtain a National Pollutant Discharge Elimination System/State Disposal System (NPDES/SDS) construction storm water permit from the Minnesota Pollution Control Agency for any project that disturbs five acres or more of land.)
(c) For disturbed areas less than five acres sedimentation basins are encouraged, but not required, unless specifically required by the City Engineer. The applicant shall install erosion and sediment controls at locations directed by the city. Minimum requirements include silt fences, rock check dams, or other equivalent control measures along slopes. Silt fences are required along channel edges to reduce sediment reaching channel. Silt fences, rock check dams, and the like must be regularly inspected and maintained.
(7) Sediment basins related to impervious surface area. Where a project’s ultimate development replaces surface vegetation with one or more acres of cumulative impervious surface, and all runoff has not been accounted for in a local unit of government’s existing storm water management plan or practice, the runoff must be discharged to a wet sedimentation basin prior to entering waters of the state. (At a minimum the work must conform with the current version of the Minnesota Pollution Control Agency’s publication, Protecting Water Quality in Urban Areas, and the current requirements found in the same agency’s NPDES/SDS permits for storm water associated with construction activities.)
(8) Generally, sufficient silt fence will be required to hold all sheet flow runoff generated at an individual site, until it can either infiltrate or seep through silt fence’s pores.
(9) Temporary stockpiling of 50 or more cubic yards of excess soil on any lot or other vacant area will not be allowed without issuance of a grading permit for the earth moving activity in question.
(10) For soil stockpiles greater than ten cubic yards the toe of the pile must be more than 25 feet from a road, drainage channel or storm water inlet. If such stockpiles will be left for more than seven days, they must be stabilized with mulch, vegetation, tarps or other means. If left for less than seven days, erosion from stockpiles must be controlled with silt fences or rock check dams. (If for any reason a soil stockpile of any size is located closer than 25 feet from a road, drainage channel or storm water inlet, and will be left for more than seven days, it must be covered with tarps or controlled in some other manner.)
(11) All sand, gravel or other mining operations taking place on the development site shall have a National Pollutant Discharge Elimination System General Storm Water permit for industrial activities and all required Minnesota Department of Natural Resources permits.
(12) Temporary rock construction entrances may be required wherever vehicles enter and exit a site.
(13) Parking is prohibited on all bare lots and all temporary construction entrances, except where street parking is not available. Gravel entrances are to be used for deliveries only as per the development contract.
(14) Streets must be cleaned and swept whenever tracking of sediments occurs and before sites are left idle for weekends and holidays. Establishment of a regular sweeping schedule is encouraged.
(15) Water (impacted by the construction activity) removed from the site by pumping must be treated by temporary sedimentation basins, geotextile filters, grit chambers, sand filters, up-flow chambers, hydro-cyclones, swirl concentrators, or other appropriate controls. Such water shall not be discharged in a manner that causes erosion or flooding of the site, receiving channels, adjacent property or a wetland.
(16) All storm drain inlets must be protected during construction until control measures are in place with either silt fence or an equivalent barrier that meets accepted design criteria, standards and specifications as contained in the latest version of the Minnesota Pollution Control Agency’s publication, Protecting Water Quality in Urban Areas.
(17) Catch basins. All newly installed and rehabilitated catch basins must be provided with a sump area for collecting coarse-grained material. Such basins must be cleaned when they are half-filled with material.
(18) Roof drain leaders. All newly constructed and reconstructed buildings must route roof drain leaders to pervious areas (not natural wetlands) where the runoff can infiltrate. The discharge rate shall be controlled so that no erosion occurs in the pervious areas.
(19) Follow-up inspections must be performed by the city on a regular basis to ensure that erosion and sediment control measures are properly installed and maintained. In all cases the inspectors will attempt to work with the developer and/or builder to maintain proper erosion and sediment control at all sites. (In cases where cooperation is withheld, construction stop orders may be issued by the city, until erosion and sediment control measures meet specifications. A second erosion and sediment control/grading inspection must then be scheduled and passed before the final inspection will be done.)
(20) Removal of more than one acre of topsoil shall not be done, unless written permission is given by the City Engineer. Excessive removal of topsoil can cause significant soil erosion problems.
(21) Inspection and maintenance. All storm water pollution control management facilities must be designed to minimize the need of maintenance, to provide easy vehicle and personnel access for maintenance purposes and be structurally sound. These facilities must have a plan of operation and maintenance that ensures continued effective removal of the pollutants carried in storm water runoff. The city or its designated representative shall inspect all storm water management facilities during construction, during the first year of operation and at least once every five years thereafter. The city will keep all inspection records on file for a period of six years. It shall be the responsibility of the applicant to obtain any necessary easements or other property interests to allow access to the storm water management facilities for inspection and maintenance purpose.
(H) Permanent storm water pollution controls.
(1) The applicant shall either install, construct, or pay the city fees for all storm water management facilities necessary to manage increased runoff, so that the discharge rates from storm water treatment basins so that the pre-development two-year, ten-year, and 100-year peak storm discharge rates are not increased. These pre-development rates shall be based on the last ten years of how that land was used. Accelerated channel erosion must not occur as a result of the proposed land disturbing or development activity. An applicant may also make an in-kind or a monetary contribution to the development and maintenance of community storm water management facilities designed to serve multiple land disturbing and development activities undertaken by one or more persons, including the applicant.
(2) All calculations and information used in determining these peak storm discharge rates shall be submitted along with the storm water pollution control plan.
(3) The applicant shall consider reducing the need for storm water management facilities by incorporating the use of natural topography and land cover such as natural swales and depressions as they exist before development to the degree that they can accommodate the additional flow of treated (such as settled) water without compromising the integrity or quality of the wetland or pond. (Commentary: The sensitivity of a wetland to degradation varies with the type of vegetation. Sedge meadows, open bogs and swamps, coniferous bogs, calcareous fens, low prairies, lowland hardwood swamps, and seasonally flooded basins are highly sensitive to degradation. Flood plain forests, reed canary grass meadows, shallow (reed canary grass, cattail, giant reed or purple loosestrife) marshes are only slightly sensitive to degradation. See the current version of the Minnesota Pollution Control Agency’s publication Storm- Water and Wetlands: Planning and Evaluation Guidelines for Addressing Potential Impacts of Urban Storm-Water and Snow-Melt Runoff on Wetlands for details.)
(4) The following storm water management practices must be investigated in developing the storm water management part of the storm water pollution control plan in the following descending order of preference:
(a) Protect and preserve as much natural or vegetated area on the site as possible, minimizing impervious surfaces, and directing runoff to vegetated areas rather than to adjoining streets, storm sewers and ditches.
(b) Flow attenuation of treated storm water by use of open vegetated swales and natural depressions;
(c) Storm water wet detention facilities (including percolation facilities); and
(d) A combination of successive practices may be used to achieve the applicable minimum control requirements specified in division (H). The applicant shall provide justification for the method selected.
(I) Minimum design standards for storm water wet detention facilities. At a minimum these facilities must conform to the most current technology as reflected in the current version of the Minnesota Pollution Control Agency’s publication, Protecting Water Quality in Urban Areas and the current requirements found in the same agency’s NPDES permits for storm water associated with construction activities.
(J) Minimum protection for natural wetlands.
(1) Runoff must not be discharged directly into wetlands without appropriate quality (such as treated) and quantity runoff control, depending on the individual wetland’s vegetation sensitivity. See the current version of the Minnesota Pollution Control Agency’s publication, Storm-Water and Wetlands: Planning and Evaluation Guidelines for Addressing Potential Impacts of Urban Storm-Water and Snow- Melt Runoff on Wetlands for guidance. (Commentary: The sensitivity of a wetland to degradation varies with vegetation type. Sedge meadows, open bogs and swamps, coniferous bogs, calcareous fens, low prairies, lowland hardwood swamps, and seasonally flooded basins are highly sensitive to degradation, while flood plain forests, reed canary grass meadows, shallow (reed canary grass, cattail, giant reed or purple loosestrife) marshes are only slightly sensitive to degradation.)
(2) Wetlands must not be drained or filled, wholly or partially, unless replaced by either restoring or creating wetland areas of at least equal public value. Compensating for the impact by replacing or providing substitute wetland resources or environments with those of at least equal public value. Compensation, including the replacement ratio and quality of replacement should be consistent with the requirements outlined in the rules adopted by the Board of Water and Soil Resources to implement the Wetland Conservation Act of 1991 including any and all amendments to it.
(3) Work in and around wetlands must be guided by the following principles in descending order of priority:
(a) Avoid both the direct and indirect impact of the activity that may destroy or diminish the wetland.
(b) Minimize the impact by limiting the degree or magnitude of the wetland related activity and its implementation.
(c) Rectify the impact by repairing, rehabilitating, or restoring the affected wetland environment with one of at least equal public value.
(d) Reduce or eliminate the adverse impact over time by preservation and maintenance operations during the life of the activity.
(K) Vegetated buffer protection for rivers, streams and wetlands.
(1) At the minimum a 100-foot wide protective buffer strip (40 feet for wetlands) of, if possible pre-development vegetation shall be left along each bank, providing a tree canopy in the buffer zone closest to the channel. Buffer width shall be increased at least two feet (four feet for wetlands) for every one 1% of slope of the surrounding land. (Commentary: When new buffer vegetation is planted, “native”Buffer Zones and Soil Bioengineering.)
(a) Detailed buffer design is usually site specific. Therefore the City Engineer can require a larger buffer that the minimum.
(b) 1. For newly constructed buffer sites the design criteria should follow common principles and the example of nearby natural areas. The site should be examined for existing buffer zones and mimic the slope structure and vegetation as much as possible. Buffer design and protection during construction should do any or all of the following: slow water runoff, trap sediment, enhance water infiltration, trap fertilizers, pesticides, pathogens, heavy metals, trap blowing snow and soil, and act as corridors for wildlife. How much stress is put on these functions will determine the buffer zone’s final configuration. (Commentary: Native Minnesota plant species have root systems and growth characteristics that are well suited to buffer functions. root systems and growth characteristics that are well suited to buffer functions. Byway of comparison, deep rooted native grasses have a root system that is about ten times greater that soy beans or corn. Useful guides for starting the species selection includes the Minnesota Department of Transportation’s seeding manual, and their “Plant Selection Matrix” CD ROM. Good plant species design stresses diversity and allows plant succession and zoning of species from wet soil preference to drier upland species.) Useful guides for starting the plant selection include Minnesota Department of Transportation’s seeding manual and their “Plant Selection Matrix” CD ROM. Good plant species design stresses diversity and allows plant succession and zoning of the species from wet soil species to drier upland species.)
2. The Minnesota Department of Natural Resources requires permits when vegetation is introduced downgrade of a water’s “ordinary high water mark.” The Minnesota Department of Natural Resources’ area hydrologist defines the ordinary high water mark. Planting permits are obtained from the Minnesota Department of Natural Resources regional fisheries office.
(c) The applicant and/or developer shall maintain the buffer strip for the first year. After that the city, or a party designated by the city, shall maintain the buffer strip. (Commentary: Even after a buffer strip is established it will require periodic inspection and possibly maintenance to ensure that it is functioning properly. Otherwise siltation and channeling may short-circuit the strip’s function.)
(d) Drain tiles will short-circuit the benefits of vegetated buffer strips. Therefore drain tiles on the development site should be identified and rendered inoperable.
(e) Buffer strips can be made into perpetual conservation easements.
(f) Buffer strips shall be marked as such with permanent signs.
(2) Water courses used solely for drainage, such as road side ditches, are exempt from this provision.
(L) Additional special trout stream and outstanding resource value water requirements.
(1) For discharges directly to or to tributaries directly to Minnesota Department of Natural Resources designated trout streams, and Minnesota Pollution Control Agency designated Outstanding Resource Value Waters there shall be no increase in either the volume or rate of discharge from any design storm with a statistical recurrence interval of less than ten years (such as for the two-year, five- year, and the like, storm events), unless diversion is not practical and/or the soil is not suitable for storm water infiltration techniques. This pertains to discharges directly to or upstream of such waters. (Commentary: The intent is to encourage either storm water infiltration or diversion, since urban trout streams are a unique resource and therefore deserve special consideration. Residential development increases the total volume of runoff resulting from a given storm. Since there is a larger volume of water to deal with, limiting the rate of storm runoff to pre-development rates means that high, flows (and therefore scouring velocities) will persist for longer periods of time than during pre-development conditions. This increases channel erosion. Infiltration or diversion deals with this increased scouting problem by lessening the volume of runoff and therefore the duration of the scouring velocities. In the case of trout streams, increasing the inputs of warm storm water increases the impact of thermal shocks. Since trout are temperature sensitive, increasing thermal shocks adversely impacts trout habitat.)
(a) The phrase, “tributaries directly to,” refers to tributaries within at least one Minnesota Department of Natural Resources Division of Waters minor watershed of the designated water. At its discretion the city may extend this area of protection.
(b) The phrase, “soil not suitable for storm water infiltration techniques,” means soils with permeability values less that Group C soils (less than 2.5 inches per hour) as defined by the U.S. Department of Agriculture’s Natural Resources Conservation Service and a high water table is not present.
(2) During construction temporary sedimentation basins are required for disturbed areas over one acre.
(3) Storm water treatment devices that remove oil and floatable material (such as basin outlets with submerged entrances) must be part of BMP systems.
(4) Where feasible lightly used vehicle traffic areas such as overflow parking lots should use pervious surfaces where feasible.
(5) If the proposed project site includes a tributary that currently experiences erosion and/or sedimentation problems, the applicant shall work with the city to include channel modifications in the project that will also address the existing erosion and/or sedimentation problem.
(6) Permanent buildings erected on sites that border directly on and all tributaries to a Minnesota Department of Natural Resources designated trout stream and/or a Minnesota Pollution Control Agency designated Outstanding Resource Value Water must not be occupied until the permanent vegetative cover has been established. Such cover must meet this permit’s definition of “final stabilization.”
(7) The applicant shall consider methods for reducing the amount of impervious surface on the site. (Commentary: A useful publication is Better Site Design: A Handbook for Changing Development Rules in Your Community available from the Center for Watershed Protection in Ellicott City, Maryland.) Suggestions include:
(a) Disking in compost or in some other manner increasing the porosity of the soil that will be come covered by lawns. (Commentary: The movement of heavy vehicles associated with construction activities compacts the soil, and thus decreases its ability to absorb water. This is true even for some types of sandy soils. The common grasses chosen for lawns do not have a deep enough root system to overcome construction vehicle related soil compaction problems.)
(b) Reduced road widths.
(c) Eliminating paving in the center of culs-de-sac.
(d) Reducing sidewalk widths.
(e) Allowing and providing for shared parking.
(f) Installing semipermeable/permeable or porous paving.
(g) Vegetated swales instead of curb and gutter.
(h) Filter strips
(i) “Green” (vegetated) roofs.
(M) Models/methodologies/computations. Hydrologic models and design methodologies used for the determining runoff characteristics and analyzing storm water management structures must be approved by the City Engineer. Plans, specifications and computations for storm water management facilities submitted for review must be sealed and signed by a registered professional engineer. All computations must appear in the plans submitted for review, unless otherwise approved by the City Engineer.
(Ord. 01-01, passed 4-10-01)