Secondary and Cumulative Impacts Master Management Plan - 2014

SECTON 6 – MITIGATION FOR SECONDARY AND CUMULATIVE IMPACTS

Stormwater control is accomplished through the installation of best management practices (BMPs) with designs approved by the Stormwater Administrator. Before being approved, BMP design plans must include a determination that no facility will cause flooding or drainage problems for adjacent structures, a designation of easements needed for inspection and maintenance of facilities, and a plan for maintenance. Control facilities may include both structural and nonstructural elements, such as dry basins; wet ponds; detention swales; underground pipe storage; and facilities to encourage overland flow, slow flow, and flow through buffer zones. At a minimum, stormwater facilities must be able to manage the 1, 2, and 10-year design storms, and BMPs must be designed to safely pass the 100-year storm. All BMPs must also be designed to meet the minimum requirements of the NCDENR Stormwater BMP Manual. To ensure long-term maintenance of stormwater facilities, all privately owned facilities must develop maintenance agreements with the Town. As part of the agreement, the Town is allowed access to inspect facilities and ensure that they are being maintained in working order. Maintenance agreements are recorded in the Wake County Register of Deeds and are binding on all subsequent owners of private discharge facilities. The Town maintains publicly owned, regional discharge control facilities. The Town requires both a performance guarantee and maintenance security requirement for BMPs, in the amount of 150 percent and 30 percent, respectively, of the engineer’s estimate cost of the BMP. The performance guarantee runs until the Town gives final approval of the required BMP (UDO Section 7.4 and Section 8). The maintenance security remains in escrow with the Town in perpetuity. The owner of each stormwater control structure will submit a Maintenance Inspection Report annually, conducted by a qualified professional, licensed in the state of North Carolina. All private and Town BMPs are inspected at least once a year by the Town’s Stormwater Inspector. 6.2.5.2 NPDES Phase II Stormwater Program The Town received a renewal of its NPDES permit on November 11, 2011 (Appendix F). The Phase II Permit requires that any new development that exceeds the 24 percent built-upon area must implement stormwater BMPs. The Town requires that all development, regardless of percent BUA, must provide stormwater BMPs. These BMPs are required to treat the runoff from the first 1.0 inches of rain, remove 85 percent average annual total suspended solids (TSS) and draw down the treatment volume no faster than 48 hours, but no slower than 120 hours. The Town requires treatment of the runoff from the first 1.5 inches of rain. The pre-development and post-development peak flows must be equivalent, regardless of the level of imperviousness in a given development. Section 5.5 of the Town’s UDO outlines required open space regulations for both residential and non-residential land uses, ranging from 5 to 20 percent, depending on the land use type and district. Article 3 of the UDO, regarding zoning, specifies the maximum lot coverage allowed, per zoning category, although open space and buffer requirements may further limit lot coverage. The Town has an Illicit Discharge Detection and Elimination (IDDE) program, as part of its NPDES Phase II permit (UDO Section 7. 6). The program prohibits illicit discharges, connections, and dumping to the stormwater conveyance system, and includes a provision for assessing civil penalties on violators. As a part of good housekeeping and pollution

6-29