Skip to main content
Loading…
This paragraph is included in your selections.

No land-disturbing activity shall occur except in accordance with the mandatory standards listed below. Except where more stringent standards are specified in this Ordinance, the technical standards and specifications contained in the North Carolina Erosion and Sediment Control Planning and Design Manual shall also apply. In addition, for land-disturbing activities greater than or equal to one acre, requirements within the most recent version of the State of North Carolina General Permit No. NCG010000 shall apply.

A. Buffer Zones

Except where more stringent buffer requirements are specified in Article 8, Environmental Protection, and/or Article 9, Landscaping and Buffering, the following requirements shall apply:

1. No land-disturbing activity during periods of construction or improvement to land shall be permitted in proximity to a lake or natural watercourse unless a buffer zone is provided along the margin of the watercourse of sufficient width to confine visible siltation within the 25% of the buffer zone nearest the land-disturbing activity. This subsection shall not apply to a land-disturbing activity in connection with the construction of facilities to be located on, over or under a lake or natural watercourse; and

2. Unless otherwise provided, the width of a buffer zone is measured from the top of the bank nearest edge of the disturbed area, with the 25% of the strip nearer the land-disturbing activity containing natural or artificial means of confining visible siltation.

3. Two rows of silt fence shall be placed along all buffer zones. Rows should be spaced a minimum of three feet apart.

B. Stabilization of Disturbed Land

The angle for disturbed land shall be no greater than the angle which can be retained by vegetative cover or other adequate erosion control devices or structures.

1. Ongoing Activity

a. Ground Cover

Land left exposed shall be planted or otherwise provided with temporary ground cover, devices, or structures sufficient to restrain erosion within the applicable time period after completion of any phase of grading or period of inactivity as follows: seven days for a steep slope; 10 days for a moderate slope; 14 days for land with no slope or inclination. For purposes of this section, a moderate slope means an inclined area, the inclination of which is less than or equal to three units of horizontal distance to one unit of vertical distance; and a steep slope means an inclined area, the inclination of which is greater than three units of horizontal distance to one unit of vertical distance. No other criteria apply.

Commentary: The moderate and steep slope definitions in this section are mandated by State law (S.L. 2009-486) for sedimentation and erosion control purposes. This steep slope definition differs from the steep slope definition under UDO Sec. 8.8, Steep Slope Protection Standards, which is otherwise applicable throughout the UDO.

b. Soil Stockpiles

Soil stockpiles shall be limited to the shorter of 30 feet above existing grade or half the height of adjacent existing mature tree cover. Stockpiles shall be wrapped in two rows of silt fence, and groundcover shall be planted in accordance with this section. Stockpile slopes shall be 2:1 or flatter.

2. Completed Activity

For any area of land-disturbing activity where grading activities have been completed, temporary or permanent ground cover sufficient to restrain erosion shall be provided as soon as practicable, but in no case later than seven days after completion of grading.

C. Stabilization of Sedimentation and Erosion Control Devices

Whenever land-disturbing activity exceeds 12,000 square feet, the person conducting the land-disturbing activity shall install such sedimentation and erosion control devices and practices as are sufficient to retain the sediment generated by the land-disturbing activity within the boundaries of the tract during construction upon and development of such tract, and shall plant or otherwise provide a temporary ground cover sufficient to restrain erosion generated by such devices and practices within seven days.

D. Erosion and sedimentation control measures, structures and devices shall be so planned, designed and constructed as to provide protection from the calculated maximum peak of runoff from the 25-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 calculation procedures acceptable to the Sedimentation and Erosion Control Officer or designee.

E. Each sediment basin or trap in the Suburban or Rural Tier shall have a minimum volume of 3,600 cubic feet per acre of disturbed area and a minimum surface area of 435 square feet per cfs of Q25 (25-year storm) peak inflow. Each sediment basin or trap in the Downtown, Compact Neighborhood, or Urban Tier shall have a minimum volume of 1,800 cubic feet per acre of disturbed area and a minimum surface area of 325 square feet per cfs of Q25 peak inflow. A skimmer shall be used in each sediment basin or trap. If the temporary sediment basin or trap is to be converted to a permanent stormwater control measure and the volume is greater than that of the temporary basin, the larger of the two shall be used, unless approved in writing by the Durham County Erosion Control Office.

F. Sediment basins and traps shall be designed and constructed such that the basin will have a settling efficiency of at least 70% for the 40-micron (0.04mm) size soil particle transported into the basin by the runoff of that two-year storm that 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 the State or the United States or any generally recognized organization or association.

G. Sediment basins and traps shall not be installed in perennial or intermittent streams.

H. Existing ponds and lakes shall not be used as sediment basins or traps.

I. Developer shall retain control of permitted area, including sediment basins or traps, until permit has been closed. For commercial sites, sold outparcels shall be permitted separately.

J. Newly constructed open channels shall be designed and constructed with side slopes no steeper than two horizontal to one vertical if a vegetative cover is used for stabilization, unless soil conditions permit steeper slopes 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.

K. Additional areas may be added per the criteria enumerated in this section only if the basin or trap is properly installed and maintained.

L. In high quality water (HQW) zones, Lake Michie/Little River Critical Area (M/LR-A), Lake Michie/Little River Protected Area (M/LR-B), Falls/Jordan Critical Area (F/J-A), Eno River Critical Area (E-A), and Third Fork Creek Watershed, uncovered areas shall be limited at any time to a maximum total area of 20 acres. In high quality water (HQW) zones, only the portion of the land-disturbing activity within a HQW zone shall be governed by this section. Larger areas within HQW may be uncovered with the written approval of the Director of DEQ, Division of Energy, Mineral and Land Resources. Larger areas within all other zones may be uncovered with the written approval of the Durham County Erosion Control Office.

M. Triassic Soil Specific Requirements

Triassic soils do not respond as well to conventional erosion control measures as listed within this section and projects with underlying Triassic soils are thus subject to the following additional requirements:

1. Flocculants shall be used on site in accordance with the requirements of paragraph 12.10.4N.

2. Sediment basins and traps shall have a minimum volume of 5,400 cubic feet per acre of disturbed area and shall be designed so as to dewater in a minimum of four days.

3. Moderate and steep slopes shall be stabilized by either matting or hydroseeding in order to more rapidly provide groundcover.

N. Flocculants

Flocculants are chemicals that can cause fine particles to combine and settle in detained runoff. When used in conjunction with sediment basins or traps, they can reduce sediment in discharge leaving a site. The use of flocculants, where not required by paragraph 12.10.4M, is recommended in land disturbing activity. When used, the following requirements apply:

1. A flocculant application plan shall be included on the erosion control plan, including:

a. Type of flocculant to be used including manufacturer and supplier;

b. Site-specific dosing systems;

c. Location(s) of flocculant application; and

d. Identification of the individual and/or position responsible for dosing and monitoring of flocculant usage.

2. Soil samples should be obtained from areas where flocculants will be used, and samples should be screened using jar tests with multiple flocculants to select the appropriate flocculant. Jar testing can be performed by the contractor or flocculant supplier.

3. Only flocculants listed on the NCDEQ website as an approved product for use in North Carolina shall be used.

4. Flocculant applied in solid form should be evaluated and re-applied if needed after every rainfall event that is equal to or exceeds 0.5 inches.

5. Flocculants shall not be applied directly to surface waters.

6. Flocculants shall be applied upstream of a sediment basin, trap, or other pooling device such as silt fence.

7. The use of flocculants does not alter the requirements for site stabilization. Sites should be stabilized as soon as possible using conventional methods to minimize the need to use flocculants.

Commentary:Additional information on the use of chemical treatment of construction site stormwater can be found at: https://cals.ncsu.edu/crop-and-soil-sciences/extension/publications/ (scroll down from top to find Erosion, Sediment, and Turbidity Control section).