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3) RateNolume Control. a) Discharge rates leaving the site must not exceed the current rates for the 2, 10 and 100-year, critical duration (24-hour) storm events, using a Type II storm distribution and antecedent moisture conditions 2 (AMC-2). The runoff from pervious and impervious areas within the model shall be modeled separately (i.e. Weighted Q, SBUH weighting, etc). b) The City of Roseville shall apply all City standards for developments and redevelopments outside of the City limits which discharge into waterbodies or storm drainage systems within the City limits. All plan submittals shall comply with City of Roseville storm water regulations. c) For development and redevelopment projects affecting stormwater problem areas identified in the City's SWMP, the City requires the applicant to incorporate such practices to resolve a proportionate share of the problem through a reduction based on existing runoff volumes. 1) The "problem" as defined by the City is that excess volume of water that either causes a downstream storm sewer system to exceed a 10-year/24-hour design capacity or causes a downstream waterbody to exceed its designated 100-year flood elevation at a given point. 2) Within an identified area, the applicant shall provide peak rate control for the 2, 10 and 100 year 24- hour rainfall events beyond the existing condition peak rate of runoff by reducing the peak rate to <80% of the existing condition. 4) Design Computations. a) Hydrologic Data Format: All hydrologic data shall be completed using NRCS methodology; i.e. HydroCAD or TR20, XP-SWMM or a comparable, City approved method. The runoff from pervious and impervious areas within the model shall be modeled separately (Weighted Q or SBUH weighting, etc). b) Rainfalls: Rainfall amounts for hydrologic analysis shall be based on the precipitation frequency estimates of NOAA Atlas 14 for the 24-hour return period from 1 to 100 Years. City of Roseville analyses shall use the values in the following table. Rainfall Frequency Rainfall Inches 2-Year 24-Hour 2.8 10-Year 24-Hour 4.2 100-Year 24-Hour 7.4 c) Infiltration-Prohibitive Sites: For projects not meeting the infiltration/volume control requirement as stated in Section 2(a), design engineers and applicants shall determine the pollutant removal efficiency of the best management practices (BMPs) incorporated into the site plan using the available industry standard models, including P8 (using a standard NURP particle size distribution for the analysis), PondNET or a comparable model approved by the City. d) Wet-Detention Pond Storm Water Treatment: As an alternative to preparing a site-specific model, the development may provide a treatment volume (dead storage) of not less than two and one-half (2.5) inches multiplied by the runoff coefficient calculated over the contributing drainage area to the pond. For example, a one (1) acre impervious site with a runoff coefficient of 0.90 that drains to a common treatment pond would be required to provide a dead storage volume of 0.19 acre-feet or eight thousand two hundred (8,200) cubic feet. The Natural Resources Conservation Service Method may also be used upon City approval. Page 3 of 8 DRAFT