20031410 Ver 1_More Info Letter_20040128

Michael F. Easley, Governor
William G. Ross Jr., Secretary
North Carolina Department of Environment and Natural Resources
Alan W. Klimek, P. E. Director
Division of Water Quality
Coleen H. Sullins, Deputy Director
Division of Water Quality
January 28, 2004
CERTIFIED MAIL: 7003 1010 0000 0032 2997
RETURN RECEIPT REQUESTED
Greenville Timberline, LLC
150 East Arlington Blvd, Suite E
Greenville, NC 27858
SUBJECT:
Dear Greenville Timberline, LLC:
WETLANDS 1401 GROUP
F03 0 11 2.7004

PROJECT ON HOLD FOR
ADDITIONAL INFORMATION
Merrimon Bay Subdivision
DWQ Project # 031410
Carteret County
This Office has reviewed your Pre Construction Notification application and is placing your
project on hold until we receive the following additional information:
1. The additional information provided to this office concerning diffuse flow at the proposed
road crossing is not adequate. You must provide diffuse flow from the roadside Swale that
will discharge into the buffer at the crossing. Based on the plans provided, you are proposing
that the road will have roadside swales that will outlet into the buffer;
2. In addition, you must provide diffuse flow at the end of each swale/ditch that is proposed to
discharge into the buffer. The plans show at least 7 locations besides the road crossing, where
this will occur. You must install level spreaders or BMP's at the end of each swale/ditch prior
to it discharging into the buffer. I have attached a copy of the Draft Level Spreader Design
Options from the DWQ website. Please provide a revised copy of the plans, details, and
calculations for the option you choose;
3. Please provide a cross-section detail of the culvert. Please remember that the culvert must be
designed and installed to allow for aquatic life movement, and installation of culverts in
wetlands must ensure continuity of water movement and be designed to adequately
accommodate high water or flood conditions.
Please respond within three weeks of the date of this letter by sending a copy of the information to
Noelle Lutheran and to Cyndi Karoly, 401 Wetlands Unit, 2321 Crabtree Blvd., Raleigh, NC 27604-226,
her phone number is [phone]. If we do not hear from you within three weeks, we will assume that
you no longer want to pursue this project and we will consider the project as withdrawn. If you have any
questions, please feel free to call me at [phone].
Sincerely,
Noelle Lutheran
Environmental Specialist III
cc: Cyndi Karoly -Wetlands Group
Kim Williams - Land Management Group
Noelle Lutheran - WiRO
N. C. Division of Water Quality
Wilmington Regional Office
127 Cardinal Drive Extension [phone] Customer Service
Wilmington, NC 28405 [phone] Fax [phone]
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Michael F. Easley
Governor
William G. Ross, Jr., Secretary
Department of Environment and Natural Resources
Kerr T. Stevens
Division of Water Quality
Draft Level Spreader Design Options Version 1.0 October 10, 2001
Using Level Spreaders to Provide Diffuse Flow Through Buffers for Compliance with Riparian Area Protection Rules
Level spreaders are one means of providing diffuse flow through protected buffers. It is always preferable to not
concentrate stormwater initially and provide as many outfalls as possible. This can reduce or even eliminate the need for
engineered devices to provide diffuse flow. However, this is not feasible in many cases. Some buffer protection rules such
as the Neuse, Catawba, and Tar-Pamlico Riparian Area Protection Rules do not allow direct discharges of stormwater
through the protected buffers. However, it is "allowable" with written approval from the DWQ to provide best management
practices (BMPs) that remove the nutrients or pollutants in question in order to discharge directly through the buffer.
These measures could include the use of the buffer itself as a forested filter strip, for instance, to remove the desired
substances. In addition to providing diffuse flow, level spreaders can be used to distribute flow into filter strips.
There are certain criteria that apply to every design that utilizes level spreaders to provide diffuse flow:
1) The entire system must safely pass a 10 year storm event without failing or causing erosion, gullies or rills.
2) The design of the level spreader must take into consideration site specific conditions such as topography, vegetative
cover, soil and other geologic conditions. If diffused flow is not attainable based on site conditions they should not be
used. (i.e. the slope of the natural ground away from or parallel to the level spreader should be relatively smooth in
the direction toward'the stream so that the flow will not reconcentrate.)
3) Level spreaders should have a minimum length of ten feet and an absolute, maximum length of 300 feet.
4) It is always easier to keep flow distributed than to redistribute it after collection.
5) The type and amount of vegetative ground cover must also be considered.
6) Level spreaders must be level.
Level Spreader Design Options:
Conventional level spreader design option where entire discharge is passed through the level spreader with
no bypass conveyance for larger storms:
• For grass or thick ground cover vegetation:
i) 13 feet of level spreader for every 1 cfs flow (Based on Q10 discharge)
ii) maximum length of 300 feet per level spreader
iii) Slopes of 8% or less from level spreader to top of stream bank
• For forested areas with little or no ground cover vegetation:
i) 100 feet of level spreader for every 1 cfs flow (Based on Q10 discharge)
ii) maximum length of 300 feet per level spreader
iii) slopes of 6% or less from level spreader to top of stream bank
Another conventional level spreader design technique that can be used to accommodate steeper slopes where grading is
allowed or exempt in zone 2 of protected buffers is to provide level spreaders in series as follows:
• Can be used on slopes of up to 15% for forested areas and 25% for grass or thick ground cover
• Structural level spreader just outside of zone 2 followed by a grassed berm level spreader just outside of zone 1
North Carolina Division of Water Quality, 401 Wetlands Certification Unit,
1650 Mail Service Center, Raleigh, NC 27699-1650 (Mailing Address)
2321 Crabtree Blvd., Raleigh, NC 27604-2260 (Location)
919-733-1786 (phone), 919-733-6893 (fax), htta://h2o.enr.state.nc.us/ncwetlands/
Page 2 of 2
• Maximum Q10 discharge of 1 cfs per 100 feet of level spreader for forested areas and 1 cfs per 13 feet of level
spreader for grass or thick ground cover
In some instances, because of topography, the size and imperviousness of the drainage area, or other site constraints,
conventional level spreader designs are not appropriate. However, there are alternative designs, like the ones listed
below, that would allow a level spreader to function properly by bypassing the larger discharge events. This is based on
the assumption used in designing most water quality BMPs that the "first flush" of stormwater discharge contains the
most substances of concern. These other alternatives are "allowable (require written approval from DWQ)" for protected
buffers in the Neuse, Tar-Pamlico and Catawba basins, but would not be allowable in protected buffers of the Randleman
watershed.
Level spreader with bypass for larger drainage areas that require 85% TSS removal or where lateral constraints limit the
level spreader length severely:
• Dry detention basin designed per NCDENR Stormwater BMP Manual* sized to detain 1" rain and release it over 2-5
days* through a level spreader.
• Level spreader length based on the maximum release rate discharge
• Discharges from greater than a 1" rain can be bypassed via an appropriate conveyance such as a grassed swale (rip
rap lined ditch or pipe may be used if necessary)
• Maximum discharge of 1 cfs per 100 feet of level spreader for forested areas and 1 cfs per 13 feet of level spreader
for grass or thick ground cover
*( in order to meet 85% TSS Removal criteria)
Another bypass alternative can be used that would not be considered to remove 85% TSS:
• Detention basin such as a type B silt basin preceding the level spreader
• Level spreader length based on the 1" per hour intensity storm
• A system designed to bypass the greater than 1" in per hour intensity storm through an appropriate conveyance such
as a grassed swale (rip rap lined ditch or pipe may be used if necessary)
• Maximum discharge of 1 cfs per 100 feet of level spreader for forested areas and 1 cfs per 13 feet of level spreader
for grass or thick ground cover
Yet another design that can be used in very specific areas with virtually flat slopes is a Preformed Scour Hole with a Level
Spreader Apron (typical detail attached):
• Discharge area must have virtually flat slopes such as those in flood plains or wetlands
• Must be located outside of zone 2
• B = 3 x discharge pipe size for pipes of either 15 or 18 inches B= base width (see detail)
• Maximum allowable discharge (Q10) of 6 cfs for a 15 inch pipe and 10 cfs for an 18 inch pipe
• Minimum apron width.of 4 feet.
Any of the above options will be considered acceptable if designed in accordance with the outlined criteria. Please keep in
mind that some of the above practices may still require written approval, for instance when a direct bypass discharge is
proposed through a protected buffer in the Neuse or Tar-Pamlico River Basin.

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