§42-258.
Design and Performance Standards
A.
Except as provided in §42-258 (Design and Performance Standards) B(2) of this subpart, erosion and
sedimentation control measures, structures, and devices shall be planned, designed, and constructed to
provide protection from the calculated maximum peak rate of runoff from the ten (10) year storm. Runoff
rates shall be calculated using the procedures in the USDA, Soil Conservation Service’s “National
Engineering Field Manual for Conservation Practices”, or other acceptable calculation procedures.
B.
HQW Zones. In High Quality Water (HQW) zones the following design standards shall apply:
(1)
Limit on Uncovered Area. Uncovered areas in HQW zones shall be limited at any time to a
maximum total area of 20 acres within the boundaries of the tract. Only the portion of the land-
disturbing activity within a HQW zone shall be governed by this section. Larger areas may be
uncovered within the boundaries of the tract with the written approval of the Director of the
Division of Land Resources of NCDENR.
(2)
Maximum Peak Rate of Runoff Protection. Erosion and sedimentation control measures,
structures, and devices within HQW zones shall be planned, designed and constructed to provide
protection from the runoff of the 25-year storm which produces the maximum peak rate of runoff
as calculated according to procedures in the United States Department of Agriculture Soil
Conservation Service’s “National Engineering Field Manual for Conservation Practices” or
according to procedures adopted by any other agency of this state or the United States or any
generally recognized organization or association.
(3)
Settling Efficiency. Sediment basins within HQW zones shall be designed and constructed such
that the basin will have a settling efficiency of at least 70 percent for the 40 micron (0.04
millimeter) size soil particle transported into the basin by the runoff of that two (2) year storm
which produces the maximum peak rate of runoff as calculated according to procedures in the
United States Department of Agriculture Soil Conservation Service’s “National Engineering Field
Manual for Conservation Practices” or according to procedures adopted by any other agency of
this state or the United States or any generally recognized organization or association.
(4)
Grade. Newly constructed open channels in HQW zones shall be designed and constructed with
side slopes no steeper than two (2) horizontal to one (1) vertical if a vegetative cover is used for
stabilization unless soil conditions permit a steeper slope or where the slopes are stabilized by
using mechanical devices, structural devices or other acceptable ditch liners. In any event, the
angle for side slopes shall be sufficient to restrain accelerated erosion.
(5)
Ground Cover. Ground cover sufficient to restrain erosion must be provided for any portion of a
land-disturbing activity in a HQW zone within 15 working days or 60 calendar days following
completion of construction or development, whichever period is shorter.