iv. Excess permanent nutrient offset credits acquired beyond what is required for the development may not be applied to any other development.
(2) Development Standards for Projects within both the Neuse River Basin Watershed and Cape Fear River Basin Watershed
A. Control and Treatment of Runoff Volume.
i. All projects shall meet the stormwater system design requirements set forth in 15A NCAC 02H .1003. Projects shall use a project density threshold of greater than twenty-four (>24%) percent built-upon area, whereupon high-density stormwater design is required. All engineered stormwater controls will meet the standards set in the Design Manual and the State’s Minimum Design Criteria, 15A NCAC 02H .1050 through .1062. ii. Where high-density stormwater design is required, stormwater systems shall meet the standards set forth in 15A NCAC 02H .1003(3) and be designed to control and treat the volume of runoff generated from all built-upon area by one inch of rainfall or equivalent runoff volume in one or more Primary SCMs. These projects may utilize offsite Primary SCMs dedicated to treating an area encompassing the project. B. Stormwater Runoff Rate . The measures shall control and treat the difference in stormwater runoff rate leaving the project site between the pre-and post-development conditions for, at a minimum, the 1-year, 24-hour storm, the 2-year, 24-hour storm, and the 10-year, 24-hour storm. Runoff volume drawdown time shall be a minimum of 48 hours, but not more than 120 hours.
(3) Standards for Stormwater Control Measures . The following standards shall apply for the implementation of stormwater control measures:
A. Evaluation According to Contents of Design Manual . All engineered stormwater controls and stormwater systems (also referred to as Stormwater Control Measures, or SCM) required under this section shall be evaluated by the Stormwater Administrator according to the policies, criteria, and information, including technical specifications and standards and the specific design criteria for each stormwater practice in the Design Manual. The Stormwater Administrator shall determine whether proposed engineered stormwater controls will be adequate to meet the requirements of this section.
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