Post-construction performance standards

Post-construction performance standards. (1) Applicability. This subchapter applies to all highway and non-highway transportation facility projects requiring stormwater discharge permit coverage under s. Trans 401.06 (1) , except any of the following: (a) A transportation facility with less than 10 percent connected imperviousness, based on the area of land disturbance, provided the cumulative area of all impervious surfaces is less than one acre. However, the protective area performance standard of sub. (7) shall apply. (b) Projects classified as reconditioning or resurfacing. (c) Projects classified as minor reconstruction of a highway. However, the protective area performance standard of sub. (7) shall apply. (2) SWMP. The department shall prepare and implement a written, project-specific SWMP that addresses the applicable requirements of subs. (3) to (11) for each proposed highway or non-highway transportation facility, as required under sub. (1) . Preparation of an SWMP shall begin as early in the design process as practicable, and be prepared iteratively until the department, in consultation with the DNR, provides a recommendation for final approval, as described in the department’s policy manuals. The SWMP may include, but is not limited to, forms developed by the department, water quality calculations, hydrologic and hydraulic calculations, maps, and exhibits. (3) Preservation of previous effort. For non-highway transportation facility redevelopment sites and highway reconstruction where the redevelopment or reconstruction will be replacing older development or a highway that was subject to the post-construction performance standards of either this chapter or subch. IV of ch. NR 151 in effect on or after October 1, 2004, the department shall meet the total suspended solids reduction, peak flow control, infiltration, and protective areas standards applicable to the older development or highway, or meet the standards of this subchapter, whichever are more stringent. (4) TSS performance standard. The department shall design, install, and maintain SCPs to reduce TSS carried in post-construction stormwater runoff from the highway or transportation facility as follows: (a) When designing SCPs, off-site runoff is not required to be treated; however, the volume of off-site runoff draining to the SCP shall be analyzed in determining the treatment efficiency of the SCP which may impact the capacity, efficiency, and size of the SCP. (b) For new highways and new development of non-highway transportation facilities, the design performance standard shall reduce the TSS load by 80 percent based on an average annual rainfall, as compared to no runoff management controls, except as provided in par. (d) . (c) For highway reconstruction and non-highway transportation facility redevelopment, the design performance standard shall reduce the TSS by 40 percent based on an average annual rainfall, as compared to no runoff management controls, except as provided in par. (d) . For non-highway transportation facility redevelopment, TSS performance standards only apply to runoff from parking areas and roads. (d) Notwithstanding pars. (b) and (c) , if the design cannot achieve the applicable TSS reduction performance standard, then the SWMP shall include a written, and project-specific, explanation of why that reduction level is not attainable and the total suspended solids load shall be reduced to the maximum extent practicable. (e) When performing TSS calculations use the average annual rainfall for the location closest to the project. Use 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), or as provided in the department’s policy manuals. (5) Peak discharge performance standard. (a) For new highways and new transportation facilities, the department shall design SCPs or other peak flow reduction methods to maintain or reduce the peak runoff discharge rates, to the maximum extent practicable, as compared to pre-development site conditions for the 1-year 24-hour design storm and the 2-year 24-hour design storm. Pre-development conditions shall assume “good hydrologic conditions” for appropriate existing land covers as identified in TR-55 or an equivalent methodology. The meaning of “hydrologic soil group” and “runoff curve number” are as provided in TR-55. However, if the pre-development land cover is cropland, woodland, or grassland, the runoff curve numbers shall not exceed the values in Table 1. (b) This subsection does not apply to the following: 1. Any highway transportation facility post-construction site where the discharge is directly into a lake over 5,000 acres or a stream or river segment draining more than 500 square miles. 2. A highway reconstruction site or a non-highway transportation facility redevelopment site. (6) Infiltration performance standard. (a) Groundwater limitations. When proposing permanent infiltration systems, conduct appropriate on-site testing to determine if seasonal high groundwater elevation or top of the bedrock is within 5 feet of the bottom of the proposed infiltration system. (b) Requirements. Except as prohibited or exempted in pars. (e) to (g) , design, install, and maintain site specific infiltration systems, and SCPs, when applicable, to infiltrate runoff to the maximum extent practicable in accordance with one of the following: 1. For development with low imperviousness of up to 40 percent connected imperviousness, such as parks, cemeteries, and low density residential development, infiltrate sufficient runoff volume so that the post-development infiltration volume shall be at least 90 percent of the pre-development infiltration volume, based on an average annual rainfall, except the effective infiltration area is not required to exceed one percent of the post-construction site. 2. For development with moderate imperviousness of more than 40 percent and up to 80 percent connected imperviousness, such as medium and high density residential, multi-family development, industrial and institutional development, and office parks, infiltrate sufficient runoff volume so that the post-development infiltration volume shall be at least 75 percent of the pre-development infiltration volume, based on an average annual rainfall, except the effective infiltration area is not required to exceed 2 percent of the post-construction site. 3. For development with high imperviousness of more than 80 percent connected imperviousness, such as commercial strip malls, shopping centers, and commercial downtowns, infiltrate sufficient runoff volume so that the post-development infiltration volume shall be at least 60 percent of the pre-development infiltration volume, based on an average annual rainfall, except the effective infiltration area is not required to exceed 2 percent of the post-construction site. (c) Pre-development. Pre-development condition shall be the same as specified in sub. (5) (a) . (d) Pretreatment. Before infiltrating runoff, pretreat the parking lot runoff and runoff from new road construction in commercial, industrial, and institutional areas before the runoff enters the infiltration system. Design the pretreatment to protect the infiltration system from clogging prior to scheduled maintenance and to protect groundwater quality in accordance with par. (a) . Pretreatment may include, but is not limited to, oil and grease separation, sedimentation, biofiltration, filtration, swales or filter strips. (e) Prohibited source areas. Due to potential for groundwater contamination, runoff from the following areas may not be infiltrated, unless designed to meet the requirements of par. (k) : 1. Areas associated with tier 1 industrial facilities identified in s. NR 216.21 (2) (a) , including storage, loading, and parking. Rooftop runoff infiltration may occur when the department obtains concurrence from the DNR. 2. Storage and loading areas of tier 2 industrial facilities identified in s. NR 216.21 (2) (b) . Infiltration from tier 2 parking and rooftop runoff areas may occur but runoff from parking areas may require pretreatment. 3. Infiltration of rooftop runoff from fueling and maintenance areas may occur when the department obtains concurrence from the DNR. (f) Prohibited infiltration locations. Infiltration systems shall not be located in the following areas due to potential for groundwater contamination: 1. Within 1000 feet upgradient or within 100 feet downgradient of direct conduits to groundwater. 2. Within 400 feet of a community water system well as specified in s. NR 811.12 (5) (d) 6. or within the separation distances listed in s. NR 812.08 for any private well or non-community well for runoff infiltrated from commercial, including multi-family residential, industrial, and institutional land uses or regional infiltration systems for one and two-family residential development. 3. Within areas where contaminants of concern, as defined in s. NR 720.03 (2) , are present in the soil through which infiltration will occur. (g) Exemptions. Runoff from the following locations is exempt from the infiltration performance standards; however, infiltration is allowable when the conditions of this subsection are met and approved by the department: 1. Highways. 2. Roads in commercial, industrial, and institutional land uses and arterial residential roads. 3. Parking areas and access roads less than 5,000 square feet for commercial development. 4. Parking areas and access roads less than 5,000 square feet for industrial development not subject to the prohibitions under par. (e) . 5. Redevelopment sites except as provided under sub. (3) . 6. In-fill development areas less than 5 acres. (h) Separation distances. Locate the bottom of an infiltration system in accordance with the following: 1. Infiltration systems shall be located so that the bottom of the infiltration system provides for a filtering layer of at least 5 feet between the bottom of the infiltration system and the elevation of seasonally high groundwater or the top of bedrock when the source area is one of the following land uses: a. Industrial, commercial, and institutional parking lots and roads. b. Residential arterial roads. 2. Subsurface infiltration systems receiving runoff only from roofs shall be located so that the bottom of the infiltration system is native soil or engineered soil with particles finer than coarse sand with at least 1 foot between the bottom of the infiltration system and the elevation of seasonally high groundwater or the top of bedrock. 3. Infiltration systems serving all other source areas shall be located so that the bottom of the infiltration system provides for a filtering layer of at least 3 feet between the bottom of the infiltration system and the elevation of seasonally high groundwater or the top of bedrock. 4. Notwithstanding subds. 1. to 3. , follow the applicable requirements for injection wells classified under ch. NR 815 . (i) Infiltration rate exemptions. Infiltration systems located in the following areas of slower draining soils are optional, but may be used to fulfill infiltration requirements in this section: 1. Where the infiltration rate of the soil measured at the proposed bottom of the infiltration system is less than 0.6 inches per hour using a scientifically credible field test method. 2. Where the least permeable soil horizon to 5 feet below the proposed bottom of the infiltration system using the U.S. Department of Agriculture (USDA) Soil Survey Field Method of Soils Analysis is one of the following: sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, or clay.