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� 4 � � � I �I r � f � 5 (c) The 100-year critical e�ent analysis of flood l��els, sforage volumes, and flow rates far waterbodies and stormwater management basins must ir�cfude both the 24-hour rainfall and the 10-day snowmelt events. 7he �0-day snowmelt e�en# is simulated by a 7.2anch, 10-day spring runo#f euent during which ii is assumed the ground is frozen solid and no infiltration occurs (CN set fo 1flb for all areas). S70RMWATER MANAGEMENT PLAN FRAMEWORK, (a} When a stormwater basin is nscessary, regional siting is preferred when regional tnanagement wouEd nof divert supply away from a local recharge area or groundwafer- dependent natura� resource_ In evaluating #he appropriateness of peak flow and water quality managemenf in an exisfing regionaf basin, the District will consider wheiher it pr�viously appraved #he basin anc! whetF�er the basin was designed fo� build-out of the site to the e�ent praposed. {b) A water manager�en# plan or ordinances of the lacal land use authority may contain other ar more stricf requirements t�an these rules im�ose. The stormwater management plan must conforrn to the District-approved local water management plan. (c} The proposed project must not ad�erseiy affect wafer le�el off tf�e si#e during or after canstruction. (d) A lar�dlncked basin may be provided an outlet anly if it: (1) Retains a hydrologic regime fhaf compfies with Dis#rict Wetland Altera' Rule F; (2} Provides sufficient dead storage valume #o refain #�ack-Eo-back � 00-yi 24-hour rainfafls and runoff; and (3) Does not create adverse downstream filoading or water qualiiy condifions a resuft o# increased discharge rate or volume, or att�er 3actors. WATER QUALITY AND VQL.UME CONTROL. (a) Acfi�ify creating impervious surFace shall address the use of Better Site Design (BSD) #echniques as ouflined ir� Chapter 4, "Minnesota Stormwater Manual" (MPCA, 2006 and subsequent revisions}. Better Si�e besign invol�es techniques applieci eariy in ihe design process to reduce impenrious cover, canserve natural areas and use pervious areas to more e#fectively treat stormwafer runoff and promote a treatment frain appr�acF� to runoff management. (b) Water quality and infiltration BMPs must be sized #o infiltrafe andlor retain fhe runo{f volume generafad within the contributing area by a two-year (2.8-in�h) storm under the developed condition. BMPs shall �e sefected on the basis of site-s�ecifc condifions, including soil types, depth to water table a�d the presence of kno�n or suspected contaminated soils. A site with soils classified as Hydrologic Soil Group (HSG) A or B must meet this standard through infiltrafion fiar at least that par� of the s€te where H5G A or B soil is presenf. (c) For impervious surface ot��er than net increase required to be treated during 11