Trans 401.106
Trans 401.106 Post-construction performance standard. Trans 401.106(1)(a)
(a) “Average annual rainfall" means the rainfall determined by the following year and location for the location nearest the project site: Madison, 1981 (Mar. 12-Dec. 2); Green Bay, 1969 (Mar. 29-Nov. 25); Milwaukee, 1969 (Mar. 28-Dec. 6); Minneapolis, 1959 (Mar. 13-Nov. 4); Duluth, 1975 (Mar. 24-Nov. 19).
Trans 401.106(1)(b)
(b) “TR-55" means the United States Department of Agriculture, Natural Resources Conservation Service (formerly Soil Conservation Service), Urban Hydrology for Small Watersheds, Second Edition, Technical Release 55, June 1986, or Technical Release 55 for Windows (Win TR-55), 2002.
Trans 401.106 Note
Note: TR-55 is on file with the offices of the Legislative Reference Bureau, the Secretary of State, and the Department of Transportation, Office of General Counsel. Copies may be obtained by writing to the U.S. Department of Agriculture, Natural Resources Conservation Service, Conservation Engineering Division, 14th and Independence Avenue, SW., Room 6136-S, Washington, DC 20250. The phone number for the division is: 202-720-2520, and the fax number is: 202-720-0428. TR-55 is available electronically at:
Trans 401.106(2)
(2) Plan. The department shall develop and implement a written plan that includes the requirements of subs.
(3) to
(10) for each transportation facility. This plan may be part of the erosion control plan.
Trans 401.106(3)
(3) Total suspended solids. Best management practices shall be designed, installed and maintained to control total suspended solids carried in runoff from the transportation facility as follows:
Trans 401.106(3)(a)
(a) For transportation facilities first constructed on or after January 1, 2003 by design, reduce the suspended solids load to the maximum extent practicable, based on an average annual rainfall, as compared to no runoff management controls. A reduction in total suspended solids by at least 80% meets the requirements of this paragraph.
Trans 401.106(3)(b)
(b) For highway reconstruction and non-highway redevelopment, by design, reduce to the maximum extent practicable the total suspended solids load by at least 40%, based on an average annual rainfall, as compared to no runoff management controls. A 40% or greater total suspended solids reduction shall meet the requirements of this paragraph. In this paragraph, “redevelopment" means the construction of residential, commercial, industrial or institutional land uses and associated roads as a substitute for existing residential, commercial, industrial or institutional land uses.
Trans 401.106(3)(c)
(c) Notwithstanding pars.
(a) and
(b), if the design cannot achieve the applicable total suspended solids reduction specified, the design plan shall include a written and site-specific explanation why that level of reduction is not attained and the total suspended solids load shall be reduced to the maximum extent practicable.
Trans 401.106(4)(a)
(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 site conditions for the 2-year 24-hour design storm or to the 2-year design storm with a duration equal to the time of concentration applicable to the transportation facility. Pre-development conditions shall assume “good hydrologic conditions" for appropriate land covers as identified in TR-55 or an equivalent methodology. The meaning 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 2 below shall be used.
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See PDF for table 
Trans 401.106 Note
Note: The curve numbers in Table 2 represent mid-range values for soils under a good hydrologic condition where conservation practices are used and are selected to be protective of the resource waters.
Trans 401.106(4)(b)1.
1. A transportation facility where the change in hydrology due to development does not increase the existing surface water elevation at any point within the downstream receiving surface water by more than 0.01 of a foot for the 2-year 24-hour storm or for a 2-year design storm with a duration equal to the time of concentration.
Trans 401.106 Note
Note: Hydraulic models, such as HEC-2 or an equivalent methodology, may be used to determine the change in surface water elevations.
Trans 401.106(5)(a)
(a) Except as provided in pars.
(d) to
(g), BMPs shall be designed, installed and maintained to infiltrate runoff to the maximum extent practicable in accordance with one of the following:
Trans 401.106(5)(a)1.
1. Infiltrate sufficient runoff volume so that the post-construction infiltration volume shall be at least 60% of the pre-construction infiltration volume, based on an average annual rainfall. However, when designing appropriate infiltration systems to meet this requirement, no more than 2% of the project site is required as an effective infiltration area.
Trans 401.106(5)(a)2.
2. Infiltrate 10% of the post-development runoff volume 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 2% of the project site is required as an effective infiltration area.
Trans 401.106(5)(c)
(c) 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 par.
(g). Pretreatment may include, but is not limited to, oil and grease separation, sedimentation, biofiltration, filtration, swales or filter strips.
Trans 401.106 Note
Note: To minimize potential groundwater impacts it is desirable to infiltrate the cleanest runoff. To achieve this, a design may propose greater infiltration of runoff from low pollutant sources such as roofs, and less from higher pollutant source areas such as parking lots.
Trans 401.106(5)(d)
(d) The following are prohibited from meeting the requirements of this subsection, due to the potential for groundwater contamination:
Trans 401.106 Note
Note: Runoff from tier 2 parking and rooftop areas may require pretreatment before infiltration.
Trans 401.106(5)(d)4.
4. Areas within 1000 feet upgradient or within 100 feet downgradient of karst features.
Trans 401.106(5)(d)5.
5. Areas with less than 3 feet separation distance from the bottom of the infiltration system to the elevation of seasonal high groundwater or the top of bedrock.
Trans 401.106(5)(d)6.
6. Areas with runoff from industrial, commercial and institutional parking lots and roads and residential arterial roads with less than 5 feet separation distance from the bottom of the infiltration system to the elevation of seasonal high groundwater or the top of bedrock.
Trans 401.106(5)(d)7.
7. Areas within 400 feet of a well serving a community water system as specified in ch.
NR 811 or within 100 feet of a well serving a non-community or private water system as specified in ch.
NR 812 for runoff infiltrated from commercial, industrial and institutional land uses or regional devices for residential development.
Trans 401.106(5)(d)9.
9. Any area where the soil does not exhibit any of the following characteristics between the bottom of the infiltration system and seasonal high groundwater and top of bedrock:
Trans 401.106(5)(d)9.a.
a. At least a 3-foot soil layer with 20 percent fines or greater. In this subdivision paragraph, “percent fines" means the percentage of a given sample of soil, which passes through a #200 sieve.
Trans 401.106(5)(d)9.b.
b. At least a 5-foot soil layer with 10 percent fines or greater. In this subdivision paragraph, “percent fines" means the percentage of a given sample of soil, which passes through a #200 sieve.
Trans 401.106(5)(d)9.c.
c. Where the soil medium within the infiltration system does not filter pollutants from water at least as effectively as the soils described in subd.
9. a. or
b. Trans 401.106(5)(e)
(e) Projects undertaken in the following areas are not required to meet the requirements of this subsection:
Trans 401.106(5)(e)1.
1. Areas where the infiltration rate of the soil is less than 0.6 inches/hour measured at the bottom of the infiltration system.
Trans 401.106(5)(e)2.
2. Parking areas and access roads less than 5,000 square feet for commercial and industrial development.
Trans 401.106(5)(e)3.
3. Areas in which a new project is replacing existing residential, commercial, industrial or institutional land uses or associated roads, or both.
Trans 401.106(5)(e)4.
4. Undeveloped areas of less than 5 acres located within existing urban sewer service areas and surrounded by existing, residential, commercial, industrial or institutional land uses.
Trans 401.106(5)(e)6.
6. Roads in commercial, industrial and institutional land uses, and arterial residential roads.
Trans 401.106(5)(f)
(f) 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.
Trans 401.106(5)(g)1.1. 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 as determined under ch.
NR 140. However, if specific information indicates that compliance with a preventive action limit is not achievable at that location, then the infiltration system may not be installed or shall be modified to prevent infiltration to the maximum extent practicable.
Trans 401.106(5)(g)2.
2. Notwithstanding subd.
1., the discharge from BMPs shall remain below the enforcement standard at the point of standards application, as determined under ch.
NR 140.
Trans 401.106(6)(a)
(a) In this subsection, “buffer area" means an area of land that commences at the ordinary high-water mark of lakes, streams and rivers, or at the delineated boundary of wetlands, and that is the greatest of the following applicable widths, as measured horizontally from the ordinary high-water mark or delineated wetland boundary:
Trans 401.106(6)(a)1.
1. For outstanding resource waters and exceptional resource waters, and for wetlands in areas of special natural resource interest as specified in s.
NR 103.04, 75 feet.
Trans 401.106(6)(a)2.
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, 50 feet.
Trans 401.106(6)(a)4.
4. For highly susceptible wetlands, 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 delineation shall be made in accordance with s.
NR 103.08 (1m). This paragraph does not apply to wetlands that have been completely filled in accordance with all applicable state and federal regulations. The buffer 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.
Trans 401.106(6)(a)5.
5. For less susceptible wetlands, 10 percent of the average wetland width, but no less than 10 feet nor more than 30 feet. Less susceptible wetlands include degraded wetlands dominated by invasive species such as reed canary grass.
Trans 401.106(6)(a)6.
6. For concentrated flow channels with drainage areas greater than 130 acres, 10 feet.
Trans 401.106(6)(ag)
(ag) In par.
(a) 1.,
4. and
5., determinations of the extent of the buffer 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 s.
NR 103.03.
Trans 401.106(6)(am)
(am) In this subsection, “buffer 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.
Trans 401.106(6)(b)1.1. Beginning with land acquired on or after January 1, 2003 for a transportation facility, no impervious surface that is part of a transportation facility may be constructed within a buffer area, unless the department determines, in consultation with the department of natural resources, that there is no practical alternative. If there is no practical alternative to locating an impervious part of a transportation facility within a buffer area, the transportation facility may be constructed in the buffer area only to the extent the department, in consultation with the department of natural resources, determines is reasonably necessary, and the department shall state in the erosion control plan or in the plan prepared under sub.
(2) why it is necessary to construct the transportation facility within a buffer area.
Trans 401.106(6)(b)2.
2. If a transportation facility is constructed within a buffer area, adequate sod or self-sustaining vegetative cover, such as grasses, forbs, sedges and duff layers of leaves and woody debris, of 70% or greater shall be established and maintained in the area that is the width of the buffer area, or the greatest width practical, and throughout the length of the buffer area in which the transportation facility is located. The adequate sod or self-sustaining vegetative cover required under this subdivision 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.
Trans 401.106 Note
Note: Vegetative cover may be measured using the line transect method described in the University of Wisconsin-Extension publication number A3533, titled “Estimating Residue Using the Line Transect Method". Seeding of non-aggressive vegetative cover is recommended in the buffer areas. Vegetation that is flood and drought tolerant and that has an extensive root system is preferable.
Trans 401.106(6)(b)3.
3. 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 buffer area.
Trans 401.106(6)(b)4.a.
a. Areas in which a new project, other than a highway, is replacing existing residential, commercial, industrial or institutional land uses.
Trans 401.106(6)(b)4.b.
b. Transportation facilities that cross or access surface waters, such as boat landings, bridges and culverts.
Trans 401.106(6)(b)4.c.
c. Transportation facilities from which runoff does not enter the surface water, except to the extent that vegetative ground cover is necessary to maintain bank stability.
Trans 401.106(7)
(7) Fueling and vehicle maintenance areas. 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.
Trans 401.106(8)(a)(a) BMPs may be located on a project site, or off a project site as part of a regional storm water device, practice or system.
Trans 401.106(8)(b)
(b) 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 section. Permanent BMPs may be located in non-navigable surface waters.
Trans 401.106(8)(c)
(c) Except as provided in par.
(d), post-construction runoff from a transportation facility first constructed after January 1, 2003 shall meet the requirements of this section before entering a navigable surface water.
Trans 401.106(8)(d)
(d) Post-construction runoff from any development within a navigable surface water that flows into a BMP is not required to meet the requirements of this section if all of the following apply:
Trans 401.106(8)(d)1.
1. The BMP was constructed prior to January 1, 2003 and the BMP either received a permit issued under ch.
30, Stats., or the BMP did not require a ch.
30, Stats., permit.
Trans 401.106(8)(d)2.
2. The BMP is designed to treat runoff from upland development that is constructed after the BMP was constructed.
Trans 401.106(8)(e)
(e) The discharge of runoff from a BMP, such as a wet detention pond, is subject to this chapter.
Trans 401.106(9)
(9) Timing. The BMPs required under this section shall be installed before the project site has undergone final stabilization.
Trans 401.106(10)(a)
(a) Except as provided in par.
(b), transportation facilities that use swales for runoff conveyance and pollutant removal satisfy all of the requirements of this section, if the swales are designed to the maximum extent practicable to do all of the following:
Trans 401.106(10)(a)1.
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.
Trans 401.106 Note
Note: It is preferred that tall and dense vegetation be maintained within the swale due to its greater effectiveness at enhancing runoff pollutant removal.
Trans 401.106(10)(a)2.
2. Carry runoff through a swale for 200 feet or more in length that is designed with a flow velocity no greater than 1.5 feet per second based on a 2-year 24-hour design storm or on a 2-year design storm with a duration equal to the time of concentration. If a swale of 200 feet in length cannot be designed with a flow velocity of 1.5 feet per second or less, the flow velocity shall be reduced to the maximum extent practicable.
Trans 401.106 Note
Note: The swale design may include check dams to slow runoff flows and improve pollutant removal. Transportation facilities with continuous features such as curb and gutter, sidewalks or parking lanes do not comply with the design requirements of this subsection. However, a limited amount of structural measures such as curb and gutter may be allowed as necessary to account for other concerns such as human safety or resource protection.
Trans 401.106(10)(b)
(b) Notwithstanding par.
(a), the department shall consult with the department of natural resources' liaison to the department of transportation to determine whether other provisions of this section are necessary to achieve water quality standards. This paragraph applies only to a transportation facility that has an average daily traffic of 2,500 or more, and from which the initial surface water of the state that runoff from the transportation facility directly enters is any of the following:
