(a) Responsible Party. The responsible party shall implement a post-construction stormwater management plan that incorporates the requirements of this Section.
(b) Plan. A written stormwater management plan in accordance with Section 15-3-9 and shall be implemented for each post-construction site.
(c) Requirements. The plan required under Subsection (b) shall include the following:
(1) Total Suspended Solids.
BMPs shall be designed, installed and maintained to control total suspended solids carried in runoff from the post-construction site as follows:
a. For new development, by design, reduce to the maximum extent practicable the total suspended solids load by eighty percent (80%), based on the average annual rainfall, as compared to no runoff management controls. No person shall be required to exceed an eighty percent (80%) total suspended solids reduction to meet the requirements of this Subsection.
b. For redevelopment, by design, reduce to the maximum extent practicable the total suspended solids load by eighty percent (80%), based on the average annual rainfall, as compared to no runoff management controls. No person shall be required to exceed an eighty percent (80%) total suspended solids reduction to meet the requirements of this Subsection.
c. For in-fill development under five (5) acres that occurs within ten (10) years after the effective date of this rule, by design, reduce to the maximum extent practicable the total suspended solids load by forty percent (40%), based on an average annual rainfall, as compared to no runoff management controls. No person shall be required to exceed a forty percent (40%) total suspended solids reduction to meet the requirements of this Subsection.
d. For in-fill development that occurs ten (10) or more years after the effective date of this rule, by design, reduce to the maximum extent practicable the total suspended solids load by eighty percent (80%), based on an average annual rainfall, as compared to no runoff management controls. No person shall be required to exceed an eighty percent (80%) total suspended solids reduction to meet the requirements of this Subsection.
e. Notwithstanding Subsections (c)(l)a-d above, if the design cannot achieve the applicable total suspended solids reduction specified, the stormwater management plan shall include a written and site-specific explanation as to why that level of reduction is not attained and the total suspended solids load shall be reduced to the maximum extent practicable.
(2) Oil and Grease Control.
a. All commercial or industrial developments and all other uses where the potential for pollution by oil and grease or both exists, the first half-inch (0.50") of runoff will be treated using the best oil and grease removal technology available.
b. In addition to Subsection (c)(2)a above, all fueling and vehicle maintenance areas shall, to the maximum extent practicable, have BMPs designed, installed and maintained to reduce petroleum within runoff, such that the runoff that enters waters of the state contains no visible petroleum sheen.
(3) Peak Discharge.
a. By design, BMPs shall be employed to maintain or reduce the peak runoff discharge rates, to the maximum extent practicable, as compared to pre- development conditions for the 2-year, IO-year, 25-year, and 100-year 24-hour design storm applicable to the post-construction site.
b. Separate subcatchments shall be used to model pervious and impervious areas within a watershed area located in the development site, when calculating runoff volumes and peak discharge rates.
c. Pre-development conditions shall assume "good hydrologic conditions" for appropriate land covers as identified in TR-55 or an equivalent methodology. The meanings of "hydrologic soil group" and "runoff curve number" are as determined in TR-55. However, when pre-development land cover is cropland, rather than using TR-55 values for cropland, the runoff curve numbers in Table 1 shall be used:
Maximum Pre-Development Runoff Curve Numbers - Cropland | ||||
Hydrologic Soil Group | A | B | C | D |
Runoff Curve Number | 56 | 70 | 79 | 83 |
d. Stormwater discharge from a newly developed site must have a stable outlet capable of carrying the design flow at velocities that are non-erosive to the outlet and receiving streams.
e. This Subsection of this Chapter does not apply to any of the following:
1. A post-construction site where the change in hydrology due to development does not increase the existing surface water elevation at any point within the downstream receiving water by more than 0.01 of a foot for the 2-year, 24- hour storm event.
2. A redevelopment post-construction site.
3. An in-fill development area less than five (5) acres.
(4) Land-Locked Ponds.
In areas draining to a land-locked pond, BMPs shall be designed to maintain or reduce the existing maximum 100-year floodplain elevation of the area adjacent to the pond unless the entire 100-year floodplain lies within the owner's property. This condition may be waived if the owner obtains the legal right to increase flood elevations on all properties where the flood plain is increased due to development activities.
(5) Infiltration.
BMP's shall be designed, installed, and maintained to infiltrate runoff to the maximum extent practicable in Subsection (c)(5)d-e below:
a. For residential developments, one of the following shall be met:
1. Infiltrate sufficient runoff volume so that the post-development infiltration volume shall be at least ninety percent (90%) of the pre-development infiltration volume, based on an average annual rainfall. However, when designing appropriate infiltration systems to meet this requirement, no more than one percent (1 %) of the project site is required as an effective infiltration area.
2. Infiltrate twenty-five percent (25%) of the post-development runoff from the 2-year, 24-hour design storm with a Type II distribution. Separate curve numbers for pervious and impervious surfaces shall be used to calculate runoff volumes and not composite curve numbers as defined in TR-55. However, when designing appropriate infiltration systems to meet this requirement, no more than one percent (1%) of the project site is required as an effective infiltration area.
b. For non-residential developments, including commercial, industrial and institutional development, one of the following shall be met:
1. Infiltrate sufficient runoff volume so that the post-development infiltration volume shall be at least sixty percent (60%) of the pre-development infiltration volume, based on an average annual rainfall. However, when designing appropriate infiltration systems to meet this requirement, no more than two percent (2%) of the project site is required as an effective infiltration area.
2. Infiltrate ten percent (10%) of the runoff from the 2-year, 24-hour design storm with a Type II distribution. Separate curve numbers for pervious and impervious surfaces shall be used to calculate runoff volumes, and not composite curve numbers as defined in TR-55. However, when designing appropriate infiltration systems to meet this requirement, no more than two percent (2%) of the project site is required as an effective infiltration area.
c. Pre-development condition shall be the same.
d. Before infiltrating runoff, pretreatment shall be required for parking lot runoff and for runoff from new road construction in commercial, industrial and institutional areas that will enter an infiltration system. The pretreatment shall be designed to protect the infiltration system from clogging prior to scheduled maintenance and to protect groundwater quality in accordance with Subsection (c)(3)h. Pretreatment options may include, but are not limited to, oil/grease separation, sedimentation, biofiltration, filtration, swales or filter strips.
e. Exclusions. Runoff from the following areas are prohibited from meeting the infiltration requirements of this Subsection (c):
1. Areas associated with Tier I industrial facilities identified in NR 216.21(2)(a), Wis. Adm. Code, including storage, loading, rooftop and parking.
2. Storage and loading areas of Tier 2 industrial facilities identified in NR 216(2)(b), Wis. Adm. Code.
3. Fueling and vehicle maintenance areas.
4. Areas within one thousand (1,000) feet upgradient or within one hundred (100) feet downgradient of karst features.
5. Areas with less than three (3) feet of separation distance from the bottom of the infiltration system to the elevation of seasonal high groundwater or the top of bedrock, except this Subsection (c)(3)e.5 does not prohibit infiltration of roof runoff.
6. Areas with runoff from industrial, commercial and institutional parking lots and roads and residential arterial roads with less than five (5) feet separation distance from the bottom of the infiltration system to the elevation of seasonal high groundwater or the top of bedrock.
7. Areas within four hundred (400) feet of a community water system well as specified in NR 811.16(4), Wis. Adm. Code, or within one hundred (100) feet of a private well as specified in NR 812.08(4), Wis. Adm. Code, for runoff infiltrated from commercial, industrial and institutional land uses or regional devices for residential development.
8. Areas where contaminants of concern, as defined in NR 720.03(2), Wis. Adm. Code, are present in the soil through which infiltration will occur.
9. Any area where the soil does not exhibit one (1) of the following soil characteristics between the bottom of the infiltration system and the seasonal high groundwater and top of bedrock: at least a three (3) foot soil layer with twenty percent (20%) fines or greater; or at least a five (5) foot soil layer with ten percent (10%) fines or greater. This does not apply where the soil medium within the infiltration system provides an equivalent level of protection. This Subsection (c)(3)e.9 does not prohibit infiltration of roof runoff.
f. Exemptions. Infiltration of runoff from the following areas are not required to meet the infiltration requirements of this Subsection (c)(3):
1. Areas where the infiltration rate of the soil is less than 0.6 inches/hour measured at the site.
2. Parking areas and access roads less than five thousand (5,000) square feet for commercial and industrial development.
3. Redevelopment and routine maintenance areas.
4. In-fill areas less than five (5) acres.
5. Infiltration areas during periods when the soil on the site is frozen.
6. Roads in commercial, industrial and institutional land uses, and arterial residential roads.
7. Highways provided the transportation facility is not part of a larger common plan of development or sale.
g. Where alternate uses of runoff are employed, such as for toilet flushing, laundry or irrigation, such alternate use shall be given equal credit toward the infiltration volume required by this Subsection.
h. Infiltration systems designed in accordance with this Subsection shall, to the extent technically and economically feasible, minimize the level of pollutants infiltrating to groundwater and shall maintain compliance with the preventive action limit at a point of standards application in accordance with NR 140, Wis. Adm. Code. However, if site specific information indicates that compliance with a preventive action limit is not achievable, the infiltration BMP may not be installed or shall be modified to prevent infiltration to the maximum extent practicable. Notwithstanding the above statements, the discharge from BMP's shall remain below the enforcement standard at the point of standards application.
(6) Protective Areas.
a. "Protective area" means an area of land that commences at the top of the channel of lakes, streams and rivers, or at the delineated boundary of wetlands, and that is the greatest of the following widths, as measured horizontally from the top of the channel or delineated wetland boundary to the closest impervious surface. However, in this Subsection, "protective area" does not include any area of land adjacent to any stream enclosed within a pipe or culvert, such that runoff cannot enter the enclosure at this location:
1. For outstanding resource waters and exceptional resource waters, and for wetlands in areas of special natural resource interest as specified in NR 103.04, Wis. Adm. Code: Seventy-five (75) feet.
2. For perennial and intermittent streams identified on a United States Geological Survey 7.5-minute series topographic map, or a county soil survey map, whichever is more current: Fifty (50) feet.
3. For lakes: Fifty (50) feet.
4. For highly susceptible wetlands: Fifty (50) feet. "Highly susceptible wetlands" include the following types: fens, sedge meadows, bogs, low prairies, conifer swamps, shrub swamps, other forested wetlands, fresh wet meadows, shallow marshes, deep marshes and seasonally flooded basins. Wetland boundary delineations shall be made in accordance with NR 103.0S(lm), Wis. Adm. Code. This Subsection does not apply to wetlands that have been completely filled in accordance with all applicable state and federal regulations. The protective area for wetlands that have been partially filled in accordance with all applicable state and federal regulations shall be measured from the wetland boundary delineation after fill has been placed.
5. For less susceptible wetlands: Ten percent (10%) of the average wetland width, but no less than ten (10) feet nor more than thirty (30) feet. Less susceptible wetlands include degraded wetlands dominated by invasive species such as reed canary grass.
6. In Subsections (c)(6)a.l,4 and 5, determinations of the extent of the protective area adjacent to wetlands shall be made on the basis of the sensitivity and runoff susceptibility of the wetland in accordance with the standards and criteria in NR 103.03, Wis. Adm. Code.
7. For concentrated flow channels with drainage areas greater than one hundred thirty (130) acres: Ten (10) feet.
b. This Subsection (c)(4) applies to post-construction sites located within a protective area, except those areas exempted pursuant to Subsection (c)(4)d below.
c. The following requirements shall be met:
1. Impervious surfaces shall be kept out of the protective area to the maximum extent practicable. The stormwater management plan shall contain a written site-specific explanation for any parts of the protective area that are disturbed during construction.
2. Where land disturbing construction activity occurs within a protective area, and where no impervious surface is present, adequate sod or self-sustaining vegetative cover of seventy percent (70%) or greater shall be established and maintained. The adequate sod or self-sustaining vegetative cover shall be sufficient to provide for bank stability, maintenance of fish habitat and filtering of pollutants from upslope overland flow areas under sheet flow conditions. Non-vegetative materials, such as rock riprap, may be employed on the bank as necessary to prevent erosion, such as on steep slopes or where high velocity flows occur.
3. Non-aggressive vegetative cover that is flood and drought tolerant shall be used in seeding the protective areas whenever possible.
4. Best management practices such as filter strips, swales, or wet detention basins, that are designed to control pollutants from non-point sources may be located in the protective area.
d. Exemptions. The following areas are not required to meet the protective area requirements of this Subsection:
1. Redevelopment post-construction sites.
2. In-fill development areas less than five (5) acres.
3. Structures that cross or access surface waters such as boat landings, bridges and culverts.
4. Structures constructed in accordance with Section 59.692(1v), Wis. Stats.
5. Post-construction sites from which runoff does not enter the surface water, except to the extent that vegetative ground cover is necessary to maintain bank stability.
(7) Swale Treatment for Transportation Facilities.
This Subsection is not applicable to transportation facilities that are part of a larger common plan of development or sale:
a. Applicability. Except as provided in Subsection (c)(7)b, transportation facilities that use swales for runoff conveyance and pollutant removal meet all of the requirements of this Section, if the swales are designed to the maximum extent practicable to do all of the following:
1. Be vegetated. However, where appropriate, non-vegetative measures may be employed to prevent erosion or provide for runoff treatment, such as rock riprap stabilization or check dams.
2. Carry runoff through a swale for two hundred (200) feet or more in length that is designed with a flow velocity no greater than 1.5 feet per second for the peak flow generated using either a 2-year, 24-hour design storm or a 2- year storm with a duration equal to the time of concentration as appropriate. If a swale of two hundred (200) feet in length cannot be designed with a flow velocity of 1.5 feet per second or less, then the flow velocity shall be reduced to the maximum extent practicable.
b. Exemptions. The Village Engineer may, consistent with water quality standards, require other provisions of this Section be met on a transportation facility with an average daily travel of vehicles greater than two thousand five hundred (2,500) and where the initial surface water of the state that the runoff directly enters is any of the following:
1. An outstanding resource water.
2. An exceptional resource water.
3. Waters listed in Section 303(d) of the Federal Clean Water Act that are identified as impaired in whole or in part, due to nonpoint source impacts.
4. Waters where targeted performance standards are developed under NR 151.004, Wis. Adm. Code, to meet water quality standards.
(d) General Considerations for On-Site and Off-Site Stormwater Management Measures.
The following considerations shall be observed in managing runoff:
(1) Use of Natural Topography.
Natural topography and land cover features such as natural swales, natural depressions, native soil infiltrating capacity, and natural groundwater recharge areas shall be preserved and used, to the extent possible, to meet the requirements of this Section.
(2) Emergency Overland Flow.
Emergency overland flow for all stormwater facilities shall be provided to prevent exceeding the safe capacity of downstream drainage facilities and prevent endangerment of downstream property or public safety.
(e) Location and Regional Treatment Options.
(1) BMP Use.
The BMP's may be located on-site or off-site as part of a regional stormwater device, practice or system.
(2) Post-Construction BMP's.
Post-construction runoff within a non-navigable surface water that flows into a BMP, such as a wet detention pond, is not required to meet the performance standards of this Chapter. Post-construction BMP's may be located in non-navigable surface waters.
(3) Post-Construction Runoff Standard.
Except as allowed under Subsection (d)(4) below, post-construction runoff from new development shall meet the post- construction performance standards prior to entering a navigable surface water.
(4) Exceptions to Post-Construction Runoff Standard.
Post-construction runoff from any development within a navigable surface water that flows into a BMP is not required to meet the performance standards of this Chapter if:
a. The BMP was constructed prior to the effective date of this Chapter and the BMP either received a permit issued under Chapter 30, Wis. Stats., or the BMP did not require a Chapter 30, Wis. Stats., permit; and
b. The BMP is designed to provide runoff treatment from future upland development.
(5) Runoff From Existing Development.
Runoff from existing development, redevelopment and in-fill areas shall meet the post-construction performance standards in accordance with this Subsection:
a. To the maximum extent practicable, BMP's shall be located to treat runoff prior to discharge to navigable surface waters.
b. Post-construction BMP's for such runoff may be located in a navigable surface water if allowable under all other applicable federal, state and local regulations such as NR 103, Wis. Adm. Code, and Chapter 30, Wis. Stats.
(6) Runoff Discharge.
The discharge of runoff from a BMP, such as a wet detention pond, or after a series of such BMP's is subject to this Chapter.
(7) Public Works Director Approval.
The Village Engineer may approve off-site management measures provided that all of the following conditions are met:
a. The Village Engineer determines that the post-construction runoff is covered by a stormwater management system plan that is approved by the Village of Edgar and that contains management requirements consistent with the purpose and intent of this Chapter.
b. The off-site facility meets all of the following conditions:
1. The facility is in place.
2. The facility is designed and adequately sized to provide a level of stormwater control equal to or greater than that which would be afforded by on-site practices meeting the performance standards of this Chapter.
3. The facility has a legally obligated entity responsible for its long-term operation and maintenance.
(8) Regional Treatment Option.
Where a regional treatment option exists such that the Village Engineer exempts the applicant from all or part of the minimum on-site stormwater management requirements, the applicant shall be required to pay a fee in an amount determined in negotiation with the Village Engineer. In determining the fee for post-construction runoff, the Village Engineer shall consider an equitable distribution of the cost for land, engineering design, construction, and maintenance of the regional treatment option.
(f) Alternate Requirements. The Village Engineer may establish stormwater management requirements more stringent than those set forth in this Section if the Village Engineer determines that an added level of protection is needed to protect sensitive resources.