Agenda - Environmental Policy Board - 08/04/2014

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Sec 117.384 -410 Revised July 29, 2014 to include 2013 Construction Stormwater Permit, 2013 MS4 Permit requirements and 2012 LRRWMO Third Generation Plan [ate, additions] was used. Accelerated channel erosion must not occur as a result of the proposed land disturbing or development activity. An applicant may also make an in -kind or a monetary contribution to the development and maintenance of community stormwater management facilities designed to serve multiple land disturbing and development activities undertaken by one or more persons, including the applicant. (b) Sizing of stormwater basins shall be based upon: (1) For basins that are not land locked — Available storage volume shall be based on 100 -year return period (7.1 inch Atlas 14, Anoka County), 24hr duration, SCS Type II storm with average soil moisture conditions (AMC 2) (2) For land locked areas — Available storage volume shall be established by estimating the surface elevation resulting from a 100 year/ 10 -day runoff or 100 year /10 -day snowmelt, whichever is more restrictive. In the snowmelt scenario, frozen soils shall be assumed (CN =100). The methodology used must conform to current Lower Rum River Watershed Management Organization (LRRWMO) rules. (c) Lowest Floor Elevation -The Lowest floor elevation of all development, including basements, must be at least 3 feet above the highest anticipated groundwater table, 2 feet above the designated or designed 100 -year flood elevation or 1 foot above the emergency overflow, whichever is higher. The LRRWMO rules designate a procedure for modifying these requirements. (d) Storm water volume management practices must be utilized on all new development sites. The options are: (1) Infiltrating or retaining the first one (1) inch of precipitation over the impervious surface of the site. These practices should seek to utilize pervious areas for stormwater treatment and to infiltrate stormwater runoff from driveways, sidewalks, rooftops, parking Tots and landscaped areas to the maximum extent practical to provide treatment for both water quantity and quality. (2) Retain the post construction runoff volume on the site for the 95th percentile storm. These practices shall prevent the off -site discharge of the precipitation from all rainfall events Tess than or equal to the 95th percentile rainfall event. Discharge volume reduction can be achieved by engineered infiltration, canopy interception, soil amendments, evaporation, rainfall harvesting, and /or evapotranspiration and any combination of the aforementioned practices. (3) Match the pre - development runoff conditions. 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 - project rates and the pre - project hydrograph for the 1 and 2 year 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 year 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 Tess 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. Ramsey, Minnesota, Code of Ordinances Page 8