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According to Chapter 9 of the Design Manual, hydrodynamic separators of the type proposed for this project have been approved for use as a pretreatment system in new and redevelopment projects or as a primary treatment system on redevelopment projects. According to Chapter 9 of the Design Manual, membrane filtration, of the type proposed for this project, has been approved for use as a primary treatment system on redevelopment projects. The following Table summarizes both the Water Quality Volume requirements and the treatment volumes provided. Table 9: Summary of Hydrodynamic Unit(s) SWM NYSDEC Required WQv Approved Manufactured Product Name Required Practice Design Flow Rate Treatment Flow Rate and WQv (CF) ID Variant (CFS) (MTFR) (CFS) Manufacturer Contech HYD-1 ALT 6,627 1.88 2.00 Cascade CS4 3.6 STEP 6 - Apply Volume and Peak Rate Control This report presents the pre-development and post-development features and conditions associated with the rate of surface water runoff within the study area. For both cases, the drainage patterns, drainage structures, soil types, and ground cover types are considered in this study. 3.6.1 NYSDEC Requirements for New Development Chapter 4 of the Design Manual requires that projects meet three separate stormwater quantity criteria: 1. The Channel Protection (CPv) requirement is designed to protect stream channels from erosion. This is accomplished by providing 24 hours of extended detention for the 1-year, 24- hour storm event. The Manual defines the CPv detention time as the center of mass detention time through each stormwater management practice. 2. The Overbank Flood Control (Qp) requirement is designed to prevent an increase in the frequency and magnitude of flow events that exceed the bank-full capacity of a channel, and therefore must spill over into the floodplain. This is accomplished by providing detention storage to ensure that, at each Design Point, the post-development 10-year 24-hour peak discharge rate does not exceed the corresponding pre-development rate. 3. The Extreme Flood Control (Qf) requirement is designed to prevent the increased risk of flood damage from large storm events, to maintain the boundaries of the pre-development 100-year floodplain, and to protect the physical integrity of stormwater management practices. This is accomplished by providing detention storage to ensure that, at each Design Point, the post- development 100-year 24-hour peak discharge rate does not exceed the corresponding pre- development rate. Stormwater Pollution Prevention Plan Page 11 2241067 Page 101 of 1493