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3.1 STEP 1 – Site Planning During the Site Planning process, the project site is evaluated for implementation of the green infrastructure planning measures identified in Table 3.1 of the Design Manual, in order to preserve natural resources and reduce impervious cover. Appendix C provides a description of each green infrastructure planning measure, along with a project specific evaluation. 3.2 STEP 2 – Calculate Water Quality Treatment Volume (WQv) Stormwater runoff from impervious surfaces is recognized as a significant contributor of pollution that can adversely affect the quality of receiving water bodies. Therefore, treatment of stormwater runoff is important since most runoff related water quality contaminants are transported from land, particularly the impervious surfaces, during the initial stages of storm events. 3.2.1 NYSDEC Requirements for Water Quality Volume The Design Manual requires that water quality treatment be provided for the initial flush of runoff from every storm. The NYSDEC refers to the amount of runoff to be treated as the “Water Quality Volume” (WQv). Section 4.2 of the Design Manual defines the Water Quality Volume as follows: WQv = (P)(R V )(A) 12 Where: P = 90% Rainfall Event Number Rv = 0.05 + 0.009 (I) I = Impervious Cover (Percent) A = Contributing Area in Acres This definition ensures that, all other things being equal, the Water Quality Volume will increase along with the impervious cover percentage. 3.2.2 Methodology for Redevelopment Projects Chapter 9 of the Design Manual outlines alternative WQv treatment objectives for redevelopment projects. According to Section 9.2.1.B.IV, redevelopment activities can achieve the water quality treatment objective through a combination of impervious cover reduction, standard SMPs, and alternative SMPs that provide a weighted average of at least two of the above methods, calculated as shown below. In this case, 100% of any new increase in impervious area to a given design point must be treated by approved alternate SMPs, standard SMPs, or RR techniques. %ALT = [25-(% ICRED+ %SMP+ %RR)] x 3 Where: %ALT = Percent of redevelopment impervious area treated by alternative SMP(s) %ICRED = Percent reduction in existing disturbed impervious area %SMP = Percent of redevelopment impervious area treated by standard SMP(s) %RR = Percent of redevelopment impervious area treated by runoff reduction techniques(s) Stormwater Pollution Prevention Plan Page 7 2241067 Page 97 of 1493