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028 <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 flow 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 15%(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 prepared 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 />