Unified Development Ordinance, 25th Supplement, December 2022

CHAPTER 9. ​NATURAL RESOURCE PROTECTION | Article 9.5. Watershed Protection Areas

D. Nitrogen and Phosphorous Loading 1. New Development a. Applicability

controlled on a runoff volume basis such that the post-development volume of stormwater leaving the site is equal to or less than the pre development volume of stormwater leaving the site based on the 90 th percentile storm. For the purpose of meeting this requirement for new development sites, the pre-development land cover must be assumed to be forested for the entire development site. The developer may request, and the City may approve, a design exception to this requirement based on one or more of the following criteria: i. Low infiltration rates of native soils on the site. ii. Shallow depth to seasonally high groundwater table on the site. iii. Shallow depth to bedrock on the site. iv. Other hardship approved by the Engineering Services Director based on site conditions. In requesting a design exception to this requirement, the developer must demonstrate that runoff resulting from the first inch of rainfall over the entire development site will be detained or retained using conventional stormwater treatment practices, GSI practices, or a combination. b. Except where located in areas designated in the Comprehensive Plan for higher impervious surfaces, the maximum percent of impervious surface coverage in those portions of the secondary reservoir watershed protection areas connected to both City water and sewer utilities shall not exceed 30% unless the impervious surface coverage is 3,500 square feet per lot or less; in such instances the maximum impervious surface coverage allowed shall not exceed 50%. c. When the development is located in portions of secondary reservoir watershed protection areas that are specifically designated in the Comprehensive Plan for higher impervious surfaces, the maximum impervious surface coverage may not exceed 70%; provided that the property is connected to both City water and sewer utilities. No more than 5% of the land area within any 1 secondary reservoir watershed protection area may be developed with an impervious surface coverage in excess of 50% unless approved by the North Carolina Environmental Management Commission. d. The design of wet ponds must meet the specifications and requirements found within the Stormwater Management Design Manual.

i. The following regulations apply to new development and expansions to impervious surfaces occurring on or after June 1, 2011. ii. Substitutions of impervious surface done in accordance with Sec. 10.3.5.A. are allowed provided there is no net increase in impervious surface and equal or greater stormwater control is provided. iii. Lots and structures existing prior to June 1, 2011 are not to be considered nonconforming solely because of the application of these regulations. Additions and expansions to existing impervious surfaces, uses and structures must comply with the requirements of these regulations; however, impervious surfaces existing prior to the initial application of these regulations are not to be included in the nitrogen and phosphorous loading calculations. iv. All stormwater management plans required for new development on properties located within a -FWPOD must comply with the following regulations. b. Requirement i. Nitrogen and phosphorous loads contributed by the proposed new development activity may not exceed the unit-area mass loading rates as follows: ii. The developer’s stormwater management plan must determine the load reductions necessary to comply with the above maximums by utilizing the loading calculation method prescribed in the Stormwater Control andWatercourse Buffer Manual. iii. Developments that comply with the watershed stormwater control master plan approved for its watershed protection area are exempted from the requirements of this section. Compliance with watershed stormwater control master plan must include: a) Nitrogen: 2 2/10 pounds per acre per year; and b) Phosphorus: 33/100 of a pound per acre per year.

9 – 55 Pub l i s hed De c embe r 2022

Pa r t 10 : Un i f i ed Deve l opmen t Or d i nanc e C i t y o f Ra l e i gh , No r t h Ca r o l i na

Supp. No. 25