Agenda - Public Works Committee - 06/17/2014

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Sec 117.384-410 Revised June 5, 2014 to include 2013 Construction Stormwater Permit, 2013 MS4 Permit requirements and 2012 LRRWMO Third Generation Plan [deletion;,, additions] Design and construct stormwater management practices that preserve the pre - development runoff conditions following construction. The post -construction rate, volume, and duration of discharges must not exceed the pre-proiect rates and the pre-proiect hvdroaraph for the 1 and 2 vear storms must be replicated through the site design and other appropriate processes. The practices listed above can be used to achieve this Goal. Defensible and consistent hydrological assessments and modeling methods must be used and documented. Infiltration will not be permitted and alternative practices will be required in the 10 vear capture zone of the DWSMA. Soils with infiltration rates of more than 8.3 inches per hour must be amended to reduce the infiltration rate to less than 8.3 inches per hour. Infiltration will also be prohibited in the following areas: (1) Where industrial facilities are not authorized to infiltrate industrial stormwater under an NPDES/SDS Industrial Stormwater Permit. (2) Where vehicle fueling and maintenance occur (3) With less than three (3) feet of separation distance from the bottom of the infiltration system to the elevation of seasonally saturated soils or the top of bedrock (4) Where high levels of contaminants in soil or Groundwater will be mobilized by the infiltrating stormwater (e) All calculations and information used in determining these peak storm discharge rates shall be submitted along with the stormwater pollution control plan. (f) The applicant shall consider reducing the need for stormwater management facilities by incorporating the use of natural topography and land cover such as natural swales and depressions as they exist before development to the decree that they can accommodate the additional flow of treated (e.a.. settled) water without compromising the integrity or quality of the wetland or pond. (Commentary: The sensitivity of a wetland to degradation varies with the type of vegetation. Sedge meadows, open boas and swamps, coniferous boas, calcareous fens, low prairies, lowland hardwood swamps, and seasonally flooded basins are highly sensitive to degradation. Floodplain forests, reed canary Grass meadows, shallow (reed canary Grass, cattail, Giant reed or purple loosestrife) marshes are only slightly sensitive to degradation. See the current version of the Minnesota Pollution Control Agency's publication "Storm -Water and Wetlands: Planning and Evaluation Guidelines for Addressing Potential Impacts of Urban Storm -Water and Snow -Melt Runoff on Wetlands" for details.) (g) The following stormwater management practices must be investigated in developing the stormwater management part of the stormwater pollution control plan in the following descending order of preference: (1) Protect and preserve as much natural or vegetated area on the site as possible, minimizing impervious surfaces, and directing runoff to vegetated areas rather than to adjoining streets, storm sewers and ditches; (2) Flow attenuation of treated stormwater by use of open vegetated swales and natural depressions; (3) Stormwater wet detention facilities (including percolation facilities); and (4) A combination of successive practices may be used to achieve the applicable minimum control requirements specified in subsection (a) of this section. The applicant shall provide justification for the method selected. Ramsey, Minnesota, Code of Ordinances Page 8