07/25/2007 Env Bd Packet - Laserfiche WebLink

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. Mr. James E. Studenski Page 3 July 18, 2007 Rice Creek Watershed District Rules City of Lino Lakes, Minnesota • b) For linear projects creating less than one (1) acre, rural to urban section and expansion/reconstruction, the proposed rules would drop the infiltration requirement to runoff from 0.8 inch rainfall event. (Paragraph 3(b)(ii)(c)). c) For existing impervious surface required to be treated during redevelopment pursuant to Paragraph 2(e), which states that water quality requirements will apply to all impervious surfaces if the site redevelopment would disturb 50% or more of the impervious surfaces, the standard is the 0.8 -inch event. (Paragraph 3(b)(ii)0). Peak Flow Management Current: Stormwater runoff rates for the proposed project must not exceed "pre- project" runoff rates for the critical 1 -year or 2 -year and 100 -year frequency events (Paragraph 3(b)). Pre - project runoff rates are currently calculated using curve numbers that correspond to the land use of the site just prior to development or redevelopment (existing conditions). Proposed: Stormwater runoff rates for the proposed project must not exceed "pre- settlement" runoff rates for the critical 2 -year and 100 -year frequency events for those site areas not covered by impervious surfaces in the pre - existing condition. The revised rule would define the pre- settlement condition as a prairie with the following curve numbers: 30 for Hydrologic Soil Group (HSG) A, 58 for HSG B, 71 for •commuthty HSG C, and 78 for HSG D soils (Paragraph 3(b)(iiz)). • Current: The current standards do not impose bounce or inundation period standards for wetlands except for landlocked basins. Proposed: RCWD is proposing storm bounce and inundation period restrictions for all wetlands within the watershed district based on wetland susceptibility classes. Proposed bounce and inundation standards for the RCWD wetland susceptibility classes are as follows (Paragraph 3(b)(iv)): Highly susceptible wetland Pre - development Existing Existing Moderately susceptible Pre - development + 0.5 feet Existing plus 1 day Existing plus 2 days Slightly susceptible wetland Pre - development + 1.0 feet Existing plus 2 days Existing plus 14 days Least - susceptible wetland /Lake No limit Existing plus 7 days Existing plus 21 days