07/25/2007 Env Bd Packet - Laserfiche WebLink

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Mr. James E. Studenski Page 2 July 18, 2007 Rice Creek Watershed District Rules City of Lino Lakes, Minnesota Proposed: Mill and overlay work on roads or other linear projects that does not create additional impervious surface are exempt from Rule C permit requirements (Paragraph 2(g)). Water Quality and Volume Control Current: The current rules require detention basins for water quality treatment (Paragraph 3(J)), and states a preference for a regional approach to management (Paragraph 1(a)). Proposed: The proposed rules focus on promoting on -site stormwater management by maximizing infiltration on individual sites through Better Site Design practices and advanced stormwater management to control runoff volume increases (Paragraph 1(a)). For certain site conditions where infiltration is not feasible and detention basins are required, RCWD retains its preference for regional basins (Paragraph 3 (b)(i)(a)). Current: Development resulting in the creation of impervious surfaces must infiltrate the impervious surface runoff from the Minneapolis- St.Paul median storm (0.34 inches) in 72 hours (Paragraph 3(k)). A separate provision requires treatment to the National Urban Runoff Program (NURP) standard of 50% phosphorus removal through stormwater detention (Paragraph 30(1)). Proposed: The proposed rules would combine these two criteria into a single standard requiring infiltration or where not feasible, detention, that will infiltrate and/or retain the runoff generated by the two -year (2.8- inch) storm event over the entire contributing area under proposed conditions (Paragraph 3(b)(ii)(b)). Infiltration basins are required to draw down within 48 hours from the end of the storm event (Paragraph 3(c)(i)(b)). The specific requirements are as follows: 1) For sites with Hydrologic Soil Group (HSG) soil type A or B, the stormwater management plan must meet this criteria through infiltration for that part of the site where type A or B soils exists. (Paragraph 3 (b) (ii) (b)). 2) Where infiltration is not feasible (i.e. soils do not support infiltration, inadequate separation from the groundwater table, presence of known or suspected contaminated soils), filtration is the preferred treatment method. (Paragraph 3(b)(ii)(d)). For sites with soils that do not promote infiltration (type C and D soils), the stormwater management plan shall focus on incorporation of water quality BMP's. The order of preference for BMP's is biofiltration, filtration, wetland treatment system, extended detention basin, and NURP Ponding (Paragraph 3(b)(ii)0). 3) The runoff volume infiltration/detention design standard for runoff from the 2.8 -inch storm event is modified as follows: a) Linear projects creating one (1) or more acres of increased impervious surface will be required to employ BMP's designed to retain the volume equal to the runoff from a 2.8- inch, 24 -hour storm under proposed conditions. (Paragraph 3(b)(ii)(J)). • • •