Post-construction performance standard

Post-construction performance standard. (1) Definitions. In this section: (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). (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. (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. (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: (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. (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. (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. (4) 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 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. (b) This subsection does not apply to: 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. 2. A highway reconstruction site. (5) Infiltration. (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: 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. 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. (b) Pre-development condition shall be the same as specified in sub. (4) (a) . (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. (d) The following are prohibited from meeting the requirements of this subsection, due to the potential for groundwater contamination: 1. Areas associated with tier 1 industrial facilities identified in s. NR 216.21 (2) (a) , including storage, loading, rooftop and parking. 2. Storage and loading areas of tier 2 industrial facilities identified in s. NR 216.21 (2) (b) . 3. Fueling and vehicle maintenance areas. 4. Areas within 1000 feet upgradient or within 100 feet downgradient of karst features. 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. 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. 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. 8. Areas where contaminants of concern, as defined in s. NR 720.03 (2) , are present in the soil through which infiltration will occur. 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: 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. 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. 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. (e) Projects undertaken in the following areas are not required to meet the requirements of this subsection: 1. Areas where the infiltration rate of the soil is less than 0.6 inches/hour measured at the bottom of the infiltration system. 2. Parking areas and access roads less than 5,000 square feet for commercial and industrial development. 3. Areas in which a new project is replacing existing residential, commercial, industrial or institutional land uses or associated roads, or both. 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. 5. Any area during periods when the soil at that area is frozen. 6. Roads in commercial, industrial and institutional land uses, and arterial residential roads. 7. Highways. (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. (g) 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. 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 . (6) Buffer areas. (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: 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. 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. 3. For lakes, 50 feet. 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. 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. 6. For concentrated flow channels with drainage areas greater than 130 acres, 10 feet.