2021-093 Ordinance - Laserfiche WebLink

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EXHIBIT A: CHAPTER 928 the SCM will have negligible impacts if the applicant can demonstrate one of the following conditions: (1) The entire water quality volume is recharged to groundwater. (2) The development will create less than one acre of impervious surface. (3) The development project is a redevelopment project with an ultra - urban setting, such as a downtown area, or on a site where 100 percent of the project area is already impervious surface and the stormwater discharge is directed into an existing storm sewer system. (4) The stormwater drainage system of the development discharges directly into a large river of fourth order or greater or to a lake, and where the development area is less than 5 percent of the water area upstream of the development site, unless a (TMDL) has identified water quality problems in the receiving surface water of the State. D. Stormwater Quantity Control: The Comprehensive Stormwater Management Plan shall describe how the proposed SCMs are designed to meet the following requirements for stormwater quantity control for each watershed in the development: The peak discharge rate of runoff from the Critical Storm and all more frequent storms occurring under post -development conditions shall not exceed the peak discharge rate of runoff from a l -year, 24-hour storm occurring on the same development drainage area under pre -development conditions. 2. Storms of less frequent occurrence (longer return periods) than the Critical Storm, up to the 100 -year, 24-hour storm shall have peak runoff discharge rates no greater than the peak runoff rates from equivalent size storms under pre - development conditions. The 1, 2, 5, 10, 25, 50, and 100 -year storms shall be considered in designing a facility to meet this requirement. The Critical Storm for each specific development drainage area shall be determined as follows: a. Determine, using a curve number -based hydrologic method or other hydrologic method approved by the City Engineer, the total volume (acre- feet) of runoff from a 1 -year, 24-hour storm occurring on the development drainage area before and after development. These calculations shall meet the following standards: (1) Calculations shall include the lot coverage assumptions used for full build out as proposed. (2) Calculations shall be based on the entire contributing watershed to the development area.