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� (d) Minimize land use impacts and improve operatianal and maintenance efficiency by siking s#orrnwater managemenf basins, when needed, regionally unfess local resources would be adversely affected. 2, R�GULATfON. A permit incorporating an approved stormwater management plan is required und�r this rule for new develo�men�, redevelopment, or additions fo an existing sit�, consistent with the fallowing: (a) A permit is required for industrial, commercial, instifutional ar mul#i-�r�it residential de�elopmenf or redevelo�ment only for a site at least one acre in size. (b) A permit Es required for single-farr�ily residential development or redevelopment only for a site at least fi�e acres in size. (c) Notwithstanding paragraph {b), a permit is not required for construcfion of a sinc family deiached dwelling on an unplatt�d lot. � (d) The site size thresholds of paragraphs {a} and (b) and fhe exception of paragra (c) do not apply if the site is: (�) (2) (3) Within fhe i00-year f[oodplain; Wffhin �,000 feet of a public water or protected wetland; or Within 300 feet of Rice CreefC, Clearwater Creek, Hardwood Creek or a public ditch. (e) lf,redevelopment will (i) disturb fifty perceni or more af existing impervious surface or (ii) increase impervious surface by fifty percent or more, t�e requiremen# ofi paragraph 5(b} wili account for alf impervious surface on the site. Far the purpose ofi this paragraph, the extent af ciist�rbance is the area of exposure of underlying sails. This paragraph do�s not apply to public linear projects subject to paragraph 5(f�. (fj A permit is not required for cansfruction o�i an individual lot within a residential subdi�ision if it confonr�s to a development plan approved by the District. {g) A permif is requir�d for p�blic ]inear proj�cts except for mill and overiay of a public roadway, sidewalk or trail that does nat create additional impervious surface. � 3. STORMWATER MANAG�MENT PLAN MODELING REQUIREMENTS. (a} A i�ydrograph method or com�uter program based on Natural Resources � Conservation Service Technical Release #20 {TR-20) and subsequeni guidance must 1�e �rsed to analyze stormwater runoff for the design ar ana�ysis af Flows and water Isvels within and off the project site. Composite Curve Numbers shall nof include directly connected � impervious surfa�es. (b) En detarmining CuNe Nurnbers to model runoff in the post-develapment condition, the Hydrologic Soil Group (HSG) of areas wit�in construc#ion l�mits is to be shifted down one classiftcation (or'/ classification for HSG A) to account for the impacts o# grading on soil structure unless the project specifications incorporate soif amendments in accordance with District Soil Amendmenf Guidelines. m