(A) Any applicant for a permit resulting in site disturbance that creates 6,000 square feet of new impervious surface or fully reconstructs one or more acre of impervious surface must meet all of the following storm water performance goals.
(1) New development volume control. For new, nonlinear developments on sites without restrictions, storm water runoff volumes will be controlled and the post-construction runoff volume shall be retained on site for one and one-tenth inches of runoff from all impervious surfaces on the site.
(2) Redevelopment volume control. Nonlinear redevelopment projects on sites without restrictions that create or fully reconstruct impervious surfaces shall capture and retain on site one and one-tenth inches of runoff from the new and/or fully reconstructed impervious surfaces.
(3) Linear development volume control.
(a) Linear projects on sites without restrictions that create new and/or fully reconstructed impervious surfaces, shall capture and retain the larger of the following:
1. Fifty-five hundredths of an inch of runoff from the new and fully reconstructed impervious surfaces on the site; or
2. One and one-tenth inches of runoff from the net increase in impervious area on the site.
(b) Mill and overlay and other resurfacing activities are not considered fully reconstructed.
(B) Sites with restrictions (as found in the MIDS design sequence flowchart).
(1) If a site has restrictions where infiltration is not feasible or advised as determined by the applicant and agreed to by the city or as determined by the city, the applicant shall follow one of the flexible treatment options (summarized in the design sequence flow chart in Appendix H).
(2) Applicant shall attempt to fully comply with the appropriate performance goals described above. Options considered and presented shall examine the merits of relocating project elements to address varying soil conditions and other constraints across the site. If full compliance is not possible due to any of the factors listed below, the applicant shall document the reason. If site constraints or restrictions limit the full treatment goal, the following flexible treatment options shall be used: applicant shall document the flexible treatment options sequence starting with Alternative #1. If Alternative #1 cannot be met, then Alternative #2 shall be analyzed. Applicants must document the specific reasons why Alternative # 1 cannot be met based on the factors listed below. If Alternative #2 cannot be met, then Alternative #3 shall be met. Applicants must document the specific reasons why Alternative #2 cannot be met based on the factors listed below. When all of the conditions are fulfilled within an alternative, this sequence is completed.
(3) Volume reduction techniques considered shall include infiltration, reuse, and rainwater harvesting, and canopy interception and evapotranspiration and/or additional techniques included in the MIDS calculator and the state’s Storm Water Manual. Higher priority shall be given to BMPs that include volume reduction. Secondary preference is to employ filtration techniques, followed by rate control BMPs.
(4) Factors to be considered for each alternative will include:
(a) Shallow bedrock;
(b) High ground water;
(c) Hotspots or contaminated soils;
(d) Drinking water source management areas or within 200 feet of drinking water well;
(e) Zoning, setbacks, or other land use requirements; and
(f) Poor soils (infiltration rates that are too low or too high, problematic urban soils).
(C) Alternative #1: Applicant shall attempt to comply with and document the following conditions.
(1) Achieve at least fifty-five hundredths volume reduction from all impervious surfaces if the site is new development, or from the new and/or fully reconstructed impervious surfaces for a redevelopment site.
(2) Remove 75% of the annual TP load from all impervious surfaces if the site is new development or from the new and/or fully reconstructed impervious surfaces for a redevelopment site.
(3) Options considered and presented shall examine the merits of relocating project elements to address varying soil conditions and other constraints across the site.
(D) Alternative #2: Applicant shall attempt to comply with and document the following conditions.
(1) Achieve volume reduction to the maximum extent practicable.
(2) Remove 60% of the annual TP load from all impervious surfaces if the site is new development or from the new and/or fully reconstructed impervious surfaces for a redevelopment site.
(3) Options considered and presented shall examine the merits of relocating project elements to address varying soil conditions and other constraints across the site.
(E) Alternative #3: Off-site treatment. Mitigation equivalent to the performance of one and one-tenth inches of volume reduction for new development or redevelopment as described above in this section, including banking or cash, can be performed off-site to protect the receiving water body. Off-site treatment shall be achieved in areas selected in the following order of preference:
(1) Locations that yield benefits to the same receiving water that receives runoff from the original construction activity;
(2) Locations within the same Department of Natural Resource (DNR) catchment area as the original construction activity;
(3) Locations within the next adjacent DNR catchment area upstream; and
(4) Locations anywhere within the city’s jurisdiction.
(F) The MIDS design sequence flowchart can be found in the state’s Storm Water Manual: http://stormwater.pca.state.mn.us/index.php/Flexible treatment options.
(Ord. 2016-06, passed 5-23-2016)