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o~~ <br />Service's Technical Release Number 55 (TR-55). <br />c) Putnam Method <br />d) Alternative methods must be approved by the County and the EMC <br />2. The same method must be used for both the pre- and post- development <br />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 criteria: <br />1. Increase in peak flaw between pre- and post- development conditions does not <br />exceed 10% (ten percent). <br />2. Proposed new development meets all of the following criteria: <br />a) total impervious surface is less than 1 S% (fifteen percent), and <br />b) remaining pervious surface maximizes stormwater runoff control and <br />conveyance. <br />3. Detention will cause further flooding on lands that have experience flooding <br />during previous storm events. This request for exemption must be pzepazed by a <br />North Carolina registered professional engineer and submitted in writing to the <br />Planning Director or Designee. Appeals of this decision will follow Section 7-E <br />of this Ordinance. <br />Section 7 Stormwater Management Plan <br />A. Plan Requirements <br />1. Permanent on-site BMPs must be shown as part of the Stormwater <br />Management Plan and accompany the Land-Disturbing Plan submittal. BMPs are <br />to be in accordance with the NC and MD design manuals. <br />2. All calculations for Nitrogen Export, Peak Run-off Volume, and permanent <br />BMPs designed for Nitrogen Removal must be included in the submittal of the <br />Stormwater Development Plan. <br />B. Plan Approval <br />The Enforcement Officer is authorized to approve any Stormwater Management Plan <br />which is in conformance with the performance standards specified in the Orange County <br />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 on any <br />land within the Neuse River Basin that is defined as new development under Section 5 of <br />this Ordinance unless and until a Stormwater Development Plan in compliance with the <br />requirements of this Section has been approved. <br />D. Design of Permanent Nitrogen Export Reduction BMPs <br />When a permanent nitrogen export reduction BMP is required for new development to <br />meet the requirements of this Ordinance, a North Carolina registered professional <br />22 <br />