07/25/2007 Env Bd Packet - Laserfiche WebLink

Home Search

• • • (a) Activity creating impervious surface must explicitly address the use of Better Site Design (BSD) techniques as outlined in Chapter 4, "Minnesota Stormwater Manual" (MPCA, 2006 and subsequent revisions). Better Site Design involves techniques applied early in the design process to reduce impervious cover, conserve natural areas and use pervious areas to more effectively treat stormwater runoff and promote a treatment train approach to runoff management. An applicant must show that BSD techniques were evaluated in developing the design of a proposed project and demonstrate the infeasibility or inapplicability of techniques that were rejected. (b) Water quality and infiltration BMPs must be sized to infiltrate and /or retain runoff volume generated within the contributing area by a two -year (2.8 -inch) storm under the developed condition. BMPs shall be selected on the basis of site - specific conditions, including soil types, depth to water table and the presence of known or suspected contaminated soils. A site with Hydrologic Soil Group (HSG) soil type A or B must meet this standard through infiltration for that part of the site where type A or B soil is found. (c) For existing impervious surface required to be treated during redevelopment pursuant to paragraph 2(e) above, the standard is the 0.8- inch event rather than the 2.8 -inch event. (d) Where infiltration is not feasible, filtration is preferred. Infiltration is considered not feasible where soils do not support infiltration, documented soil contaminants preclude the use of infiltration practices, or there is inadequate separation from the water table. (e) For a site or part of a site characterized by HSG C or D soils, the stormwater management plan shall focus on incorporation of water quality BMPs. The order of preference for BMP's is biofiltration, filtration, wetland treatment system, extended detention basin, NURP ponding. (f) The runoff volume infiltration /detention standard of paragraph (b) is modified for public linear (roadway, sidewalk and trail) projects as follows: New _> 1.0 acre impervious No change. New < 1.0 acre impervious Rural to Urban Section Expansion / Reconstruction BMPs must be sized for the runoff volume generated from impervious surface within the contributing area by an 0.8 -inch event. Mill & Overlay No permit required. DRAFT DOCUMENT 11