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APPENDIX B – WAKE COUNTY PROGRAMS TO MITIGATE SECONDARY AND CUMULATIVE IMPACTS
B-18
The County created a Stormwater Management Section within its Environmental
Services Department, whose goal is to minimize the impacts of stormwater runoff. The
department staff is charged with upholding the local, state, and federal regulations
related to stormwater, including:
Floodplain management
Sediment and erosion control
WSW protection
Neuse River Basin NSW stormwater rules
National Pollutant Discharge Elimination System (NPDES) Phase II Stormwater
Regulations
Stormwater management permits are also required. The County requires the use of the
Wake County Stormwater Hybrid Design Tool for all stormwater management
submittals. Its purpose is to streamline the many different stormwater requirements and
facilitate a more timely review and approval of stormwater management plans.
Complete stormwater requirements can be found in the 2014 Wake County Stormwater
Manual: Submittal and Design Guidance. The purpose of this document is to provide
guidance for the management of stormwater runoff resulting from development in the
County’s jurisdiction. It provides support to Article 9 of the UDO and applicable State
regulations, which establish minimum requirements to address impacts of stormwater
runoff associated with new development and expansions.
The County requires that the pre-development peak runoff rate be maintained. If the
difference between pre- and post- runoff exceeds 10 percent for the 1-year, 24-hour
storm then the developer must mitigate peak flow within the drainage area. Nitrogen
export must not exceed of 3.6 pounds per acre per year (lbs/acre/year) in the Neuse
River. The County additionally requires that residential post-development curve
number not exceed target curve numbers. Article 9, Part 2 of the UDO requires volume
management for target curve number matching.
The County has established a stormwater credit system that provides incentives for
better site design and the locating of new development in areas that cause less impact to
aquatic resources. Approved methods to receive credit include: disconnected
impervious surfaces, reforestation, and cluster and open space subdivisions. These
stormwater practices reduce generation of stormwater, reduce size and cost of
stormwater storage, and provide partial removal of pollutants.
The County has impervious surface limitations in its WSWs. The impervious surface
limitations range from 6 to 30 percent for residential areas, and up to 30 percent for non-
residential areas. Under NPDES Phase II rules, development that exceeds 24 percent is
required to implement stormwater best management practices (BMPs). Stormwater
permits are required for non-residential projects that cumulatively disturb more than 0.5
acre.
Wake County is required to implement the Neuse River and Jordan Lake NSW
stormwater rules, as previously described, and stormwater program submittals are
required for developments to ensure compliance with the rules. These rules supersede
the Neuse Rules within the Jordan Lake watershed portion of the Cape Fear River Basin.