07/25/2007 Env Bd Packet - Laserfiche WebLink

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extent proposed. (b) A stormwater management plan must conform to the District - approved local water management plan. (The proposed project must not adversely affect water level off the site during ortf er construction. (d) A landlocked basin may be provided an outlet only if it: (1) Retains a hydrologic regime that complies with District Wetland Alteration Rule F; (2) Provides sufficient dead storage volume to retain back -to -back 100 -year, 24 -hour rainfalls and runoff; and (3) Does not create adverse downstream flooding or water quality conditions as a result of increased discharge rate or volume or other factors. (11) Water Quality and Volume Control. (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. r 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. DRAFT DOCUMENT 14 • •