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SECTON 6 – MITIGATION FOR SECONDARY AND CUMULATIVE IMPACTS
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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