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a) Rational Method <br /> b) Peak Discharge Method as described in the USDA Soil <br /> Conservation Service's Technical Release Number 55 (TR-55). <br /> c) Putnam Method <br /> d) Alternative methods must be approved by the County and the <br /> EMC <br /> 2. The same method must be used for both the pre- and post- <br /> development conditions. <br /> 3. Raleigh Rainfall Depths <br /> a) 1 year, 24 hour depth: 3.00 inches <br /> b) 1 year, 24 hour intensity: under development by DWQ staff <br /> E. Exemptions to the Peak Flow Requirements <br /> Peak flow requirements are waived for development that meets the following <br /> criteria: <br /> 1. Increase in peak flow between pre- and post- development conditions <br /> does not exceed 10% (ten percent). . <br /> 2. Proposed new development meets all of the following criteria: <br /> a) total impervious surface is less than 15%(fifteen percent), and <br /> b) remaining pervious surface maximizes stormwater runoff <br /> control and conveyance. <br /> 3. Detention will cause further flooding on lands that have experience <br /> flooding during previous storm events. This request for exemption must be <br /> prepared by a North Carolina registered profession engineer and submitted <br /> in writing to the Planning Director or Designee. Appeals of this decision <br /> will follow Section 7-E of this Ordinance. <br /> Section 7 Stormwater Management Plan <br /> A. Plan Requirements <br /> 1. Permanent on-site BMP's must be shown as part of the Stormwater <br /> Management Plan and accompany the Land-Disturbing Plan submittal. <br /> BMP's are to be in accordance with the NC and MD design manuals. <br /> 2. All calculations for Nitrogen Export, Peak Run-off Volume, and <br /> permanent BMP's designed for Nitrogen Removal must be included in the <br /> submittal of the Stormwater Development Plan. <br /> B. Plan Approval <br /> The Enforcement Officer is authorized to approve any Stormwater Management <br /> Plan which is in conformance with the performance standards specified in the <br /> Orange County Design Manual, and other requirements of this Ordinance. <br /> C. Approved Plan a Prerequisite <br /> The Enforcement Officer is not authorized to issue any permits for development <br /> on any land within the Neuse River Basin that is defined as new development <br /> under Section 5 of this Ordinance unless and until a Stormwater Development <br /> 25 <br />