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DR. J.H. CARTER III & ASSOCIATES, INC.
Environmental Consultants
P.O. Box 891 • Southern Pines, N.C. 28388
(910) 695-1043 9 Fax (910) 695-3317
Letter of Transmittal
To Attn: Ian McMillian
Division of Water Quality 401
Wetlands Unit
2321 Crabtree blvd
Raleigh NC, 27604
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Date:6-19-09 Job #0759
Attn:Ian McMillian
Re: Johnston Community college permit info
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5 6-17-09 5 Stormwater and Erosion/Sediment Control information additional mapping
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Endangered Species Surveys 9 Environmental Assessments 9 Land Management 9 Wetlands Mapping and Permitting
Here is the additional information you requested for the Johnston County College
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NCDENR Stormwater BMP Manual
8. Level Spreaders
Revised 09-28-07
Level spreaders do not remove pollutants by themselves, but they are so crucial in
assuring the effectiveness of certain BMPs and in protecting the function of riparian
buffers that an entire chapter is devoted to them in this manual. Potential locations for a
level spreader include, but are not limited to, the following:
- The inlet of a bioretention cell or an infiltration basin, where a level spreader can
reduce inlet velocities and diffuse flow for proper stormwater treatment.
- Prior to a restored riparian buffer or a filter strip, where a level spreader can
diffuse the flow to allow the vegetation to effectively remove pollutants.
- Prior to a stormwater discharge to a riparian buffer or a wetland, where a level
spreader can diffuse the flow into the vegetated area to prevent erosion and
allow for pollutant removal.
8.1. General Characteristics
A level spreader consists of a concrete linear structure constructed at virtually zero
percent grade. Depending on the use of the level spreader, other elements may include
a high flow bypass system, a forebay and a filter strip. If the level spreader is not
outleting to a bioretention cell or another infiltration system, it will outlet to a filter strip.
The filter strip is defined as the land between the outlet of the level spreader continuing
downslope to the top of the stream bank or other surface water. Often, the filter strip
consists of the 50-foot wide area beside a stream or other surface water that is protected
by one of the Riparian Area Protection Rules. Outside of areas covered by Riparian Area
Protection Rules, the filter strip must be a minimum of 30 feet in width. A filter strip is
not required if the purpose of the level spreader is to outlet to wetlands.
One of the main purposes of a level spreader is to disperse concentrated stormwater
flows over a wide enough area to prevent erosion of the BMP or filter strip where it
outlets. Erosion can undermine a BMP, and an eroded filter strip can be a significant
source of sediment pollution to the streams and other natural water bodies. The other
main purpose of a level spreader is to increase the interaction between the stormwater
and the vegetation and soils in the BMP or filter strip. The vegetation and soils bring
about pollutant removal via filtration, infiltration, absorption, adsorption, and
volatilization.
A level spreader may be used as a stand-alone device or as part of a larger BMP system.
For example, a level spreader may also be used to diffuse the outflow of a BMP through
a filter strip. If the flow from a drainage area exceeds the capacity of a level spreader,
another BMP such as a dry extended detention basin or a wet detention pond may be
used before the level spreader to attenuate the flow to an appropriate rate.
Level Spreader 8-1 July 2007
NCDENR Stormwater BMP Manual
Revised 09-28-07
Figure 8-1:
Plan View of a Level Spreader (adapted from Hathaway 2006)
Filter Strip: Could be a riparian buffer, vegetated
Flow Bypass filter strip or restored riparian buffer.
Structure %
From Watershed
Forebay
Reinforced Channel
Receiving
Stream
Reinforced Swale
(necessary if level
spreader is designed for
the 1 in/hr storm)
Level Spreader Lip / #57 Stone on Fabric
Length =13' to 130'
(parallel to contour lines)
Figure 8-2:
Profile View of a Level Spreader (adapted from, Hathaway 2006)
Level Spreader Lip ,
3' Layer of
Flow Path: 1Y #57 5tone
Riparian BLdTer
n / or Filter Strip
Channel
3 ft Wide
Une4rcirain - 5aed 5tnp of
for 5rte Sod filter Fabrc
Condltlon5 - Drain Appropnately 5aed
Into Bypass Swalc Concrete Footer
Level Spreader 8-2 July 2007
NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
8.2 Siting for Level Spreaders Used With Filter Strips
A filter strip, as stated previously, is simply the land between the level spreader and the
receiving stream. This land could consist of a protected riparian area, a vegetated buffer
required by another stormwater program, a restored riparian buffer, or a filter strip used
as a BMP (see Chapter 13 for appropriate design). Regardless of the reason for
constructing or protecting the filter strip, it is important to determine whether the site is
appropriate for a level spreader. In order to do this, the designer will need to gather the
following information:
- The peak flows during the one inch per hour intensity storm and the ten-year
storm,
- The topography of the proposed filter strip (obtained during a field visit),
and
- A characterization of the vegetation in the proposed filter strip (obtained and
photographed during a field visit).
After the field visit, the filter strip vegetation should be characterized as one of the
following:
- Grass: an area that is densely covered with grass.
- Thick ground cover: a natural or naturalized area containing that is densely
covered with a mixture of grasses, shrubs and herbs. Some trees may be
present, but they are not the predominant species. The vegetation must be
allowed to grow and not be cut back.
- Forest: an area that is densely wooded with a ground cover of mulch or
leaves.
One required characteristic of all three types of filter strip vegetation is that it be dense,
with no areas of bare soil. If existing vegetation is not dense, then the filter strip should
be enhanced with additional plants so that it will not erode as stormwater flow is
diffused across it.
Once the above information is obtained, the designer has enough information to
determine whether the site is appropriate for a level spreader. The following criteria
must be met depending on the vegetation in the filter strip:
- Filter strips with grass or thick ground cover: Slopes must be less than or equal
to 8% for filter strips and the flow resulting from the 1 inch per hour intensity
storm may not exceed 10 cfs.
- Filter strips with forest vegetation: Slopes must be less than or equal to 6% and
the flow resulting from the 1 inch per hour intensity storm may not exceed 2
cfs.
- Filter strips with a combination of either grass or thick ground cover AND forest
vegetation: Slopes must be less than or equal to 6% and flow requirements are
met (see Design and Construction section for computing flow limits for a
combined vegetation filter strip).
In addition, for all vegetation types, uniform, diffuse flow must be possible (i.e., no
draws may be present in the filter strip).
Level Spreader 8-3 July 2007
NCDENR Stormwater BMP Manual
Revised 09-28-07
Level spreaders are not appropriate when one or more of the following conditions exist:
- There is a draw located within the filter strip downslope of the proposed
level spreader.
- The stormwater flows exceed the above guidelines unless another BMP is
installed to attenuate the flow before it is discharged to the level spreader.
- The slope in the filter strip exceeds the above guidelines unless DWQ
approves level spreaders to be placed in series (explained in the paragraph
below).
Level spreaders must be placed outside of protected riparian areas unless the designer
obtains a variance from the Environmental Management Commission. In addition, they
may only be installed where the existing filter strip topography is appropriate and the
stormwater flow will not exceed the capacity of the level spreader. If diffuse flow is not
achievable based on site topography and stormwater flow rate, level spreaders may not
be used. Other BMP choices for areas where level spreaders are not appropriate will be
discussed in the Design and Construction section.
If a filter strip exceeds the allowable slopes given above and up to a 15% maximum
slope, installing level spreaders in series is a possibility if it can be shown that no other
solution is practicable. Level spreaders in series may be approved by DWQ on a case-by-
case basis following a site visit. Placing level spreaders in series will require siting a
level spreader within a protected riparian area; therefore, a variance will be required
from the Environmental Management Commission. See the Design and Construction
section for appropriate placement of level spreaders in series.
It is important to site the level spreader in a location where safe and legal access is
available for construction and maintenance.
8.3 Design and Construction
A level spreader system the drainage area consists of up to separate four parts (see
Figures 8-1 and 8-2 above):
1. Flow Bypass System: A diverter box (or other type of flow splitter) that passes all
flow above the one inch per hour intensity to a swale capable of safely passing
the ten-year storm without eroding. A flow bypass system is not needed if the
level spreader lip is constructed to be long enough to handle the flow from the
ten-year storm. Also, if the level spreader is receiving flow from another BMP
such as a wet detention basin, then a forebay is not needed.
2. Forebay: A bowl-shaped feature that slows the stormwater runoff and settles out
some sediment and debris. If the level spreader is receiving flow from another
BMP such as a wet detention basin, then a forebay is not needed.
3. Level Spreader Lip: The main body of the level spreader that receives water from
the forebay (or directly from a BMP). The concrete lip is constructed so that it is
level along its entire length. A swale is constructed immediately upslope of the
level spreader lip, which allows stormwater to rise and fall evenly over the lip.
Level Spreader 8-4 July 2007
NCDENR Stormwater BMP Manual
ter Revised 09-28-07
4. Filter Strip: The densely vegetated area that receives flow from the level
spreader.
8.3.1 High Flow Bypass System
The flow bypass system must be constructed so that all flows above the one-inch per
hour intensity are diverted to a bypass channel. If the level spreader is receiving flow
from another BMP such as a wet detention pond, then a flow bypass system is not
necessary. Additionally, a flow bypass system is not necessary if the level spreader is
designed to handle the peak flow from the ten-year storm event.
For a stand-alone level spreader, high flows will be bypassed through the use of a
diverter box or other flow splitting device. Please see Section 5.3 for more information
on flow splitters.
This bypass channel must be designed to safely pass the ten-year design storm without
erosion. If there is enough sunlight in the filter strip to support it, it is preferable to use
turf reinforcement in place of riprap. This will reduce the cost of constructing the
bypass channel while increasing pollutant removal and flow capacity of the bypass
channel.
The outlet of the bypass channel must be designed to reduce the impacts to the receiving
stream. The bypass channel should be designed to enter the stream at an angle rather
than a directly perpendicular manner, which may create erosion on the opposite stream
bank. The bypass channel should discharge into a pool (deep section) of the stream. At
the point of entry, stream banks may need to be protected with riprap or other
engineered solution. Another option is to direct the bypass channel to a velocity
dissipater or to use a bypass pipe that discharges to a culvert.
Bypass channels are considered an "allowable" use within a protected riparian buffer.
Tree removal and disturbance must be minimized and a buffer authorization must be
obtained from the DWQ 401 Oversight/ Express Permitting Unit or the local delegated
buffer permitting authority.
8.3.2 Forebay
After passing through the flow bypass system, stormwater should be directed to a
forebay (unless the level spreader is receiving flow from another BMP, in which case a
forebay is not necessary). The forebay is an excavated, bowl-shaped feature that slows
the stormwater and allows sediment and debris to settle out. Horizontal angle of entry
pipe is 30° [recommended]; armor may be needed to prevent scour. Figure 8-3 shows a
schematic of a forebay specifically designed for use with a level spreader.
It is recommended that the forebay be designed so that its surface area is 0.2% of the
contributing area's impervious surface. The recommended depth is one foot at the back
end, sloping to three feet on the front side (portion closest to the inlet). A forebay is
required unless no practical alternative is demonstrated and the level spreader is
Level Spreader 8-5 July 2007
NCDENR Stormwater BMP Manual
Chapter Revised 09-28-07
maintained by a municipal stormwater utility or NCDOT. The forebay can be lined
with Class B riprap to dissipate energy. Design guidelines for the forebay provided are
recommendations based on field research. Best professional judgment should be used
with regard to forebay surface area and depth.
Figure 8-3:
Schematic of a Forebav for Use With a Level Spreader (Hathawav and Hunt 2006
Pipe: F-oni
X
lrt L C CC f
T-.
1
a
8.3.3 Level Spreader Lip
The level spreader lip consists of a grassed swale to distribute the water along the length
of a level concrete weir. Water rises and falls evenly over the lip of the level spreader,
which therefore distributes the flow evenly over its length. The lip of the level spreader
should constructed out of concrete and should be 3 to 6 inches higher than the existing
ground (downslope side) and anchored into the soil with an appropriately-sized
concrete footer. The lip shall be installed at a 0-0.05% grade (level). An under drain is
recommended to reduce ponding in the swale.
One of the most important design criteria for the level spreader lip is that it must be
constructed parallel to contour lines. Often, this will result in a level spreader that is
curved, which is perfectly acceptable.
The level spreader must be a minimum of 13 feet and a maximum of 130 feet in length
(see Table 8-1 for determining required length). The appropriate length for the level
spreader is determined based on two criteria: The type of vegetation in the filter strip
and the design flow. Significantly longer level spreaders are needed when the filter strip
is composed of forest vegetation. This is due to the fact that the forest flow is much
more susceptible to erosion than an area with grass or thick ground cover. If the level
spreader is outleting to a bioretention area or another filtration BMP, then the lengths
appropriate for a forested filter strip should be used to prevent erosion within the BMP.
Level Spreader 8-6 July 2007
NCDENR Stormwater BMP Manual Chanter Revised 09-28-07
The design flow will be based upon one of the following:
- The peak flow resulting from the one inch per hour intensity flow (in which
case a high flow bypass system and a forebay will be required).
- The peak flow resulting from the ten-year storm (in which case a forebay will
be required).
- The drawdown rate from the upslope BMP if one is present (in which case
neither a high flow bypass system or a forebay will be required).
Table 8-1: Level spreader lengths
Grass or thick ground cover filter strip Forest filter strip
13 feet of level spreader lip per 1 cfs of
flow for slopes from 0 to 8 percent 65 feet of level spreader lip per 1 cfs of
flow for slopes from 0 to 6 percent
If the filter strip is composed of a mixture of grass or thick ground cover and forest
vegetation, then the level spreader length should be determined by calculating the
weighted average of the lengths required for each vegetation type. For example, if a
level spreader is constructed adjacent to a 50-foot Neuse Riparian Buffer where Zone 2
(the outer 20 feet) will be maintained as grass and Zone 1 (the inner 30 feet) has existing
forested vegetation, the appropriate level,,Spreader length will be:
(20/50) x (13 ft/1cfs) + (30/50) x (65 ft/1 cfs) = 44.2 or 44 feet per cfs of flow
The downstream side of the level spreader should be designed to further encourage
diffuse flow of water and minimize erosion. The first 3 feet from the level spreader lip
should use geotextile fabric with a 3-4 inch deep layer of #57 stone placed on top, or
permanent erosion control matting. If geotextile fabric is used, it should be selected
based on the soil type (sand, silt or clay). The fabric should be extended 3 feet from the
level spreader lip to the downslope area in order to reduce erosion and located outside
of Zone 2 of riparian buffer.
8.3.4 Filter Strip
If the filter strip does not contain dense vegetation, it should be enhanced with
additional plantings to reduce the chance of erosion. The first 10 feet of the filter strip
downslope of the level spreader is not recommended to exceed 4 percent slope.
8.3.5 Level Spreaders in Series
b.'
If a filter strip slope exceeds 6 percent for filter strips that contain forest vegetation or 8
percent for filter strips with grass or thick ground cover up to a maximum of 15 percent
slope, installing level spreaders is a possibility if it can be shown that no other solution is
practicable. Level spreaders in series may be approved by DWQ on a case-by-case basis
following a site visit.
Level Spreader 8-7 July 2007
NCDENR Stormwater BMP Manual
Revised 09-28-07
At the higher slopes of 6 or 8 to 15 percent, level spreaders will need to be placed every
25 feet in order to maintain diffuse flow. In an area covered by a Riparian Area
Protection Rule, this will necessitate placing one level spreader just outside the buffer
(50 feet from the stream bank) and a second level spreader in Zone 1 of the buffer (25
feet from the stream bank). Constructing a level spreader in Zone 1 will require a major
variance from the Environmental Management Commission.
8.3.6 Options where Level Spreaders are not Appropriate
Level spreaders may not be installed on sites where flows are too high to be conveyed
by a 130-foot level spreader or the topography of the filter strip (if applicable) is too
steep. The option that is selected in these cases will depend if the problem results from
high flows from the drainage area or steep slopes in the filter strip.
If the flows are too high, but slopes within the filter strip are within the allowable range,
then a BMP that captures the stormwater runoff and releases it to the level spreader at a
slower rate may be installed upslope. BMPs that attenuate flow include:
- Dry extended detention basin: This BMP will eliminate the need for a high flow
bypass system and a forebay.
- Wet detention basin: This BMP will also eliminate the need for a high flow
bypass system and a forebay. One option is to use 2-1/2" floating [Faircloth]
skimmer in the pond to achieve a stable flow to the level spreader.
If the topography of the filter strip is too steep for a level spreader, a different type of
BMP will be needed. If the intended filter strip is an area protected by the Riparian
Buffer Rules, then the stormwater will have to be treated by a BMP that removes 30 or
more percent of the nutrients rather than using a level spreader. The outfall of this BMP
can then be routed directly through the buffer with written approval from the DWQ.
8.3.7 Preformed Scour Holes
Preformed scour holes are preshaped, riprap-lined basins located directly downgrade of
an outfall. The purpose of a preformed scour hole is to dissipate energy and diffuse
flow. They may be used to provide diffuse flow only when all of the following
requirements are met:
- The outfall area must be flat (less than 2 percent slope).
- The scour hole must be located outside of protected riparian areas.
The maximum allowable discharge to a scour hole from a 15-inch pipe is 6 cfs
based on the ten-year storm discharge.
The maximum allowable discharge to a scour hole from an 18-inch pipe is 10
cfs based on the ten-year storm discharge.
Pipes larger than 18 inches may not be discharged to a scour hole.
Once flow has filled the shallow basin, it overtops the preformed scour hole and is
redistributed as diffuse flow to the surrounding area. A typical example of a preformed
scour hole layout and its components is shown in Figure 8-4. Figure 8-5 is a cross
section of a typical preformed scour hole.
Level Spreader 8-8 July 2007
NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
Figure 8-4
Typical preformed scour hole layout and components (NCDOT 2006)
PIPF
A (d.715" OR I'c
NJ
(STANDARD
ROLL WICT?1;
SOUP.RF PRFFORPAE
SCOUR MOLE (PFS10
(RIPRAP IN BASIN NOT
SHOWN FOR CLARITY)
PFRLIANFr1T SOIL
1# RFiN70RCFf,.1EN- MATTING
;PSRL:1). PSRM SHALL BF
SEEDED WITH VEGETATION
AT INSTAL I.ATION
Figure 8-5
Preformed scour hole cross section (NCDOT 2006)
PIPE. PSRM
c1-15 OR 15) INSTALL LEVEL AND
???1 61FLUSI I 'i`11 Ti i W JRAL
?DEPTH OF SCOUR F1O1_E GROUND
r (1' MIN. - Y P,1AX.)
Y NATURAL
71" rt??1 GROOND
LINER: CLASS G RIPRAP j
WIT}I TYPE 2 FILTER FABRIC r,11N. 1' TUCK.
DEPTH OF RIPRAP (1'}
BASF
dVIDTH
Once these site constraints are met, the size of the preformed scour hole is calculated
based on the class of riprap used to line the hole and the diameter of the discharge pipe.
For optimum energy dissipation, the ratio of the scour hole depth should be between 16
and 32 inches deep. The basin should be stabilized with filter fabric and riprap to
absorb the impact of the discharge and to prevent additional erosion. Class B riprap
(d50 = 8 inches) should be used on top of the filter fabric to line the preformed scour
Level Spreader 8-9 July 2007
NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
hole. The minimum and maximum stone sizes for Class B riprap are 5 inches and 12
inches, respectively.
To prevent erosion immediately downgrade, an apron of permanent soil reinforcement
matting (PSRM) is required downgrade of the preformed scour hole.
Design requirements for scour holes:
- The base of the scour hole is square. The width is calculated as follows: Base
width = 3 x Discharge pipe size.
- Riprap must be Class B (d50 = 8 inches).
- Minimum width of the PSRM apron is the standard PSRM roll width.
- PSRM must be tucked a minimum of 1 foot underneath the filter fabric and
natural ground around the perimeter of the scour hole.
- Side slope for all four sides of the scour hole is 2H:1V.
- Riprap thickness is equal to 1.5 times the midrange riprap stone size (d50), or 1
foot for Class B riprap.
- Minimum depth of the scour hole is 1 foot.
- Maximum depth of the scour hole is 3 feet.
Construction requirements for scour holes:
- To avoid shifting of the scour hole after installation, the BMP should be installed
in undisturbed soil instead of in fill material.
- Install preformed scour holes after site stabilization.
- Ensure that the apron is flush with natural ground. The elevation of the top of
the preformed scour hole should be the same as the elevation of the PSRM.
- Ensure that riprap consists of a well-graded mixture of stone. Smaller-size riprap
stones should be used to fill voids between larger stones.
- Where practical, route off-site runoff away from the BMP.
- Immediately after construction, stabilize the exit areas with vegetation.
- Clear the area of all construction debris and check the exit areas for any potential
obstructions that could promote channelized flow.
Note: This entire Scour Hole section was condensed from the 2006 NC Department of
Transportation BMP Manual. DWQ appreciates their willingness to share their expertise
on scour hole design.
Level Spreader 8-10 July 2007
NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
8.4. Construction
Immediately before the level spreader is constructed, verify that ground contours are
parallel to the level spreader location called for in the plans, slopes are less than 6 to 8
percent, and that no draws are located in the filter strip adjacent to the level spreader. If
this is the case, the level spreader may need to be relocated to a more appropriate area.
Also verify in the field that the level spreader is fully 50 feet away from the stream if it is
being installed in an area covered by a Riparian Area Protection Rule.
Before construction, reassess the vegetation in the filter strip. The filter strip should be
densely vegetated prior to the construction of the level spreader. If not, additional
plantings will need to be added prior to the construction of the level spreader. If grass
cover needs to be re-established in the filter strip (only allowed within Zone 2 of a
protected riparian buffer), construction may be limited to the growing season.
The most important construction task is to insure that the level spreader is actually level.
A correctly installed level spreader will have no greater than 0.05% grade on the
spreader lip to ensure a uniform distribution of flow; otherwise water will channelize
below the structure and become a source of erosion. Level spreaders should be
constructed on undisturbed soil whenever possible. If the use of fill is unavoidable, it
shall be constructed on material compacted to 95% of standard proctor test levels prior
to seeding for that area not considered the seedbed.
The level spreader and filter strip must be protected from harm (e.g., sediment and
stormwater flows) during construction. A temporary stormwater diversion will likely
be necessary until the level spreader has fully stabilized. If the disturbed areas are
minor, they often can be stabilized with vegetative measures.
8.5. Maintenance
8.5.1. Common Maintenance Issues
During the first one or two years after construction, filter strips and level spreaders
should be inspected for proper distribution of flows and signs of erosion during and
after major storm events. After the first one or two years, the strip may be inspected
annually or biannually. If evidence of erosion exists, the eroded areas should be filled in
and reseeded. The cause of the erosion should then be determined and, if possible,
eliminated.
Filter strips that are not maintained properly may quickly become nonfunctional
(Schueler et al., 1992). Maintenance involves routine activities such as mowing,
trimming, and replanting when necessary. Strips that receive excessive sediment may
require periodic regrading and reseeding of their upslope edge because deposited
sediment can kill grass and change the elevation of the edge such that the stormwater no
longer flows through the strip in thin sheets. Maintenance requirements are as follows:
Level Spreader 8-11 July 2007
NCDENR Stormwater BMP Manual
8.5.2. Sample Inspection and Maintenance Provisions
Revised 09-28-07
Important maintenance procedures:
- Immediately after the filter strip is established, any newly planted vegetation
will be watered twice weekly if needed until the plants become established
(commonly six weeks).
- Once a year, the filter strip will be reseeded to maintain a dense growth of
vegetation
- Stable groundcover will be maintained in the drainage area to reduce the
sediment load to the vegetation.
- Two to three times a year, grass filter strips will be mowed and the clippings
harvested to promote the growth of thick vegetation with optimum pollutant
removal efficiency. Turf grass should not be cut shorter than 3 to 5 inches and
may be allowed to grow as tall as 12 inches depending on aesthetic requirements
(NIPC,1993). Forested filter strips do not require this type of maintenance.
- Once a year, the soil will be aerated if necessary.
- Once a year, soil pH will be tested and lime will be added if necessary.
After the filter strip is established, it will be inspected quarterly and within 24 hours
after every storm event greater than 1.0 inch (or 1.5 inches if in a Coastal County).
Records of inspection and maintenance will be kept in a known set location and will be
available upon request.
Inspection activities shall be performed as follows. Any problems that are found shall
be repaired immediately.
Table 8-2
Sample Inspection and Maintenance Provisions for Level Spreaders, Filter Strips and
Restored Riparian Buffers
BMP element: Potential problem: How to remediate the problem:
The entire filter strip Trash/debris is present. Remove the trash/debris.
system
The flow splitter device The flow splitter device is Unclog the conveyance and dispose
(if applicable) clogged. of an sediment off-site.
The flow splitter device is Make any necessary repairs or
damaged. replace if damage is too large for
repair.
The Swale and the level The swale is clogged with Remove the sediment and dispose
lip sediment. of it off-site.
The level lip is cracked, Repair or replace lip.
settled, undercut, eroded or
otherwise damaged.
There is erosion around the Regrade the soil to create a berm
end of the level spreader that that is higher than the level lip, and
shows stormwater has then plant a ground cover and
bypassed it. water until it is established. Provide
lime and a one-time fertilizer
Level Spreader 8-12 July 2007
NCDENR Stormwater BMP Manual
Revised 09-28-07
application.
Trees or shrubs have begun Remove them.
to grow on the swale or just
downslo e of the level lip.
The bypass channel Areas of bare soil and/or Regrade the soil if necessary to
erosive gullies have formed. remove the gully, and then
reestablish proper erosion control.
Turf reinforcement is Study the site to see if a larger
damaged or riprap is rolling bypass channel is needed (enlarge if
downhill. necessary). After this, reestablish
the erosion control material.
The filter strip Grass is too short or too long Maintain grass at a height of
if applicable). approximately three to six inches.
Areas of bare soil and/or Regrade.the soil if necessary to
erosive gullies have formed. remove the gully, and then plant a
ground cover and water until it is
established. Provide lime and a
one-time fertilizer application.
Sediment is building up on Remove the sediment and
the filter strip. restabilize the soil with vegetation if
necessary. Provide lime and a one-
time fertilizer application.
Plants are desiccated. Provide additional irrigation and
fertilizer as needed.
Plants are dead, diseased or Determine the source of the
dying. problem: soils, hydrology, disease,
etc. Remedy the problem and
replace plants. Provide a one-time
fertilizer application.
Nuisance vegetation is Remove vegetation by hand if
choking out desirable species. possible. If pesticide is used, do not
allow it to get into the receiving
water.
The receiving water Erosion or other signs of Contact the NC Division of Water
damage have occurred at the Quality local Regional Office, or the
outlet. 401 Oversight Unit at 919-733-1786.
1 NOTE: Contact NC Division of Water Quality, 401/ Wetlands Unit at 919-733-1786
BEFORE any work in Protected Riparian Buffers.
Level Spreader 8-13 July 2007
NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
September 28, 2007 Changes:
1. 8.0: Removed the reference to "sand infiltration basin" and replaced it with "infiltration
basin."
2. 8.3.6: Clarified the requirements for areas where the terrain is too steep for level spreader
use.
3. 8.5: Updated the maintenance section.
4. Figure 8-1: Altered for clarification.
5. Figure 8-2: Corrected to indicate that level spreaders can drain to either riparian buffers or
filter strips, not just buffers.
6. Table 8-1: Deleted, "If the forest vegetation is 100-150 feet wide, then the length can be
reduced to 50 feet of level spreader per 1 cfs of flow. If the forest vegetation is more than
150 feet wide, then the length can be reduced to 40 feet of level spreader per I cfs of flow."
Level Spreader 8-14 July 2007
A RMA
NCDENR
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Beverly Eaves Perdue Coleen H. Sullins Dee Freeman
Governor Director Secretary
May 21, 2009
CERTIFIED MAIL: RETURN RECEIPT REQUESTED
Mr. Herman Kight
Johnston Community College
245 College Road
Smithfield, NC 27577
DWQ Project # 09-0576
Johnston County
Subject Property: Johnston Community College Library
Ut to Neuse River [030402, 27-(41.3), WSIV, NSW, CA]
REQUEST FOR MORE INFORMATION
Dear Mr. Kight:
On May 19, 2009, the Division of Water Quality (DWQ) received your application dated May 18, 2009,
to fill or otherwise impact 1.4 acres of Isolated Wetlands to construct the proposed Johnston Community
College library at the site. The DWQ has determined that your application was incomplete and/or
provided inaccurate information as discussed below. The DWQ will require additional information in
order to process your application to impact protected wetlands and/or streams on the subject property.
Therefore, unless we receive five copies of the additional information requested below, we will place this
project on hold as incomplete until we receive this additional information. If we do not receive the
requested information, your project will be formally returned as incomplete. Please provide the following
information so that we may continue to review your project.
Additional Information Requested:
1. Please re-submit your site plans on full plan sheets at a scale of no smaller than 1 "=50' with
topographic contours shown.
2. Please indicate all wetland impacts including fill slopes on the site plan.
3. Per the requirements of the Neuse River Basin Riparian Buffer Rule, you must show that this site
meets diffuse flow requirements with a level spreader or other BMP per Chapter 8 of the BMP
Manual (see http://h2o.enr.state.nc.us/su/bmp forms.htm).
4. Please provide all site plans as required in the PCN checklist (link:
http://h2o.enr.state.nc.us/ncwetlands/documents/PCNChecklist_v 1 _4.doc)
Please submit this information within 30 calendar days of the date of this letter. If we do not receive this
requested information within 30 calendar days of the date of this letter, your project will be withdrawn and
you will need to reapply with a new application and a new fee.
401 Oversight/Express Review Permitting Unit
1650 Mail Service Center, Raleigh, North Carolina 27699-1650
Location: 2321 Crabtree Blvd., Raleigh, North Carolina 27604
Phone: 919-733-17861 FAX: 919-733-6893
Internet: http://h2o.enr.state.nc.us/ncwetlands/
NorthCarolina
?aturalCr?
An Equal Opportunity 1 Affirmative Action Employer
Johnston Community College
Page 2 of 2
May 21, 2009
This letter only addresses the application review and does not authorize any impacts to wetlands, waters or
protected buffers. Please be aware that any impacts requested within your application are not authorized (at
this time) by the DWQ. Please call Ms. Cyndi Karoly or Mr. Ian McMillan at 919-733-1786 if you have
any questions regarding or would like to set up a meeting to discuss this matter.
Sincerely, , // j
-01 Oversight/Express Review Permitting Unit
CBK/ijm
cc: Lauren Witherspoon, DWQ Raleigh Regional Office
USACE Raleigh Regulatory Field Office
File Copy
William Mullin, J.H. Carter III & Associates, Inc., 515F Midland Road, Southern Pines, NC 28387
Filename: 090576JohnstonCCU brary(Johnston)On_Hold
Version 1.4
January 9, 2009
401 Oversight/Express Permitting PCN Submittal Checklist
? The application fee (Checks may be made out to "N.C. Division of Water Quality"
- $240.00 for 401 Water Quality Certification with minor impacts
- $570.00 for 401 Water Quality Certification with major impacts
- Express Review Fee (Amount requested on Acceptance Letter)
? Five (5) complete and collated copies of the PCN Application and supporting
documentation (instead of providing 5 copies of the full size plans you may provide two
copies of full size plans along with three copies of 11 X 17 plans)
? Stormwater Management Plan (if applicable - see PCN Form Help File Section E)
1) Please provide three (3) copies of the stormwater management plans along with all
supporting information pertaining to this project including the following:
a. Entire site development/layout plans delineating all drainage areas;
b. Design calculation sheets for all proposed BMPs) sized for both on-site and
off-site drainage;
c. BMP supplements for each proposed BMP and Required Items Check List
(http://h2o.enr.state.nc.us/su/bmp forms.htm) along with all required
items;
d. A Notarized Operation & Maintenance Agreement for each stormwater
management facility;
e. Detailed construction drawing sheets shall include
(i) Erosion and sediment control plans;
(ii) Installation and planting schedules for the proposed BMPs;
(iii) Appropriately scaled plan views and cross sectional details of all
BMPs and associated components - inlet and outlet structures,
forebay, respective zones and pertinent elevations.
? If your project is located within a State implemented Riparian Buffer Rule Area, submit the
following along with site plans and PCN form:
1) Three (3) copies of the details for on-site diffuse flow provisions, (refer to
http://h2o.enr.state.nc.us/su/bmp_forms.htm).
? DWQ Stream Determination Forms for streams on property and DWQ determination
letter for wetlands or streams (if applicable).
The following is the most critical of all the information that you must provide. The quality and
detail of the information will often determine the expeditiousness of the review. The following is
a checklist of the types of pertinent information required at a minimum:
Maps and Plans:
? The most recent version of the 1:24,000 USGS Topographic Map - Please cleanly draw or
delineate the site boundaries on the topographic map.
_??.. ? The most recent version of the bound and published County NRCS Soil Survey Map -
(required for projects within the Neuse River Basin, Tar-Pamlico River Basin, Randleman
Lake Watershed and the Catawba River Basin, also recommended for all projects) -
Please clearly delineate the site boundaries, etc. on the map. If the delineation obscures
any of the features, it is recommended that a clean copy be provided. Copies of the
Version 1.4
January 9, 2009
current soil survey and/or soil survey map sheets can be obtained from the local NRCS
County Office (http://www.nc.nres.usda.gov/). GIS soil layers are not acceptable.
? Vicinity map - Please clearly mark the location and approximate boundaries of the property
and project on the map. Please indicate north arrow and scale. Please include applicable
road names or State Road numbers.
? The Site Plan - The most critical map to be provided is the site plan. You must provide full
sized plans. The following is the minimum list of plans that are typically needed.
? Pre-construction/Pre-existing conditions - This sheet (or sheets) must include:
• All jurisdictional and non-jurisdictional wetland, stream, water features, State regulated
buffers (delineated into Zones 1 and 2)
• Topographic contours with elevations
• Any existing structures and impervious areas
• Existing utility lines and easements
• Existing roads, culverts, and other pertinent features
• North arrow and the scale (1":50' scale is recommended).
? Proposed conditions - This sheet (or sheets) must include:
• All jurisdictional and non-jurisdictional wetland, stream, water features, State regulated
buffers (delineated into Zones 1 and 2)
• Lot layout (if a subdivision or commercial development is proposed) - lots must be
developable without further impacts to jurisdictional and non-jurisdictional wetlands
streams, water features, and State regulated buffers. Building envelopes must be
provided when streams, wetlands, riparian buffers, or water features exist on a lot
• All built-out structures and impervious cover
• Final grading contours with elevations
• All utilities and easements (including septic fields on all lots within 100 feet of stream,
wetland, or water features - if applicable)
• Impacted areas - these should correspond with the Impact numbers listed on your PCN
form.
? Drainage Plans - Final drainage plans must include the following:
• Locations and pertinent elevations and sizes of the stormwater collection system and
drainage ways
• All inlets and outlets must also be shown with pertinent elevations (All outlets to
wetlands must be at a non-erosive velocity, generally less than 2 ft/sec during the peak
flow from the 10-yr storm)
• Scaled stormwater BMPs must also be indicated as required by DWQ rules and policies
• In certain cases (see Section E of PCN form), final stormwater management plans must
also be provided (see Stormwater Management Plan Checklist)
? Proposed Impacts - All impacts to jurisdictional and non-jurisdictional wetland, stream,
water features, and State regulated buffers must be shown and labeled on the site plans at
a scale no smaller than 1" = 50'. All excavation, fill, flooding, stabilization, and other impacts
that will be conducted in or near jurisdictional and non-jurisdictional wetland, stream, water
features, and State regulated buffers must be indicated. Please provide cross sectional
details showing the provisions for aquatic life passage (burial of culvert 20% for culverts <_ 48
inches, and 1-foot for culverts > 48 inches).
Version 1.4
January 9, 2009
Wetland Impacts:
? Precise grading and final elevation contours must be provided. Existing
vegetation and any clearing must be specified.
? All subsurface utility lines must indicate the location of anti-seep collars.
Construction detail for anti-seep collars must be provided.
? Roadway or other crossings of riparian wetlands may require floodway culverts to
maintain existing hydrological conditions.
? Plans should show that the hydrology of remaining wetlands on the site will be
maintained.
Stream Impacts:
? Stream impacts must be clearly shown on the plans. The centerline as well as
the banks of the stream must be surveyed or located by GPS for the portion of
the stream to be impacted.
? The inlet and the outlet of all culverts should be aligned with the stream as
much as possible. Inlet and outlet elevations and streambed elevations should
be indicated. Any inlet or outlet protection must be shown and enumerated on
the impact map(s).
? For bottomless culverts or other spans, a vertical cross section should be
provided that shows the minimum distance from each span to each stream bank,
the stream cross section, the height of the span above the stream and the
minimum distance from the edge of each footer to each stream bank.
Additionally, please provide a signed and sealed geotechnical report of
subsurface soils at the proposed bottomless culvert location. The report must
comply with the Division of Highways - Guidelines for Drainage Studies and
Hydraulic Design, prepared by A. L. Hankins, Jr., State Hydraulics Engineer -
1999.
? Multiple culverts or sectioned box culverts typically require the use of sills, off-
setting or other means to match the cross section of the existing stream (in order
to maintain stream stability and provide aquatic life passage). A vertical cross
section of the culverts should be shown overlain with the up and downstream
stream cross section including the stream flood-prone area.
? Impacts associated with dam construction must indicate and enumerate all fill
associated with the dam footprint, spillway and any bank stream bank
stabilization. The length of stream impounded must also be indicated and
enumerated.
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Project area and location of the proposed Johnston Community College Library Building, Smithfield,
Johnston County, North Carolina
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EROSION AND SEDIMENT CONTROL PLAN
JOHNSTON COMMUNITY COLLEGE
LIBRARY BUILDING
245 COLLEGE ROAD
SMITHFIELD, NC 27577
JOHNSTON COUNTY
MAY 2009
PROJECT DESCRIPTION:
A new Library Building and associated site work is proposed on the south side of College Road
between Martin Luther King Drive and Highway 70 Business north of Hwy I-95 in Johnston County
of the City of Smithfield, North Carolina. The project is located within the Neuse River watershed.
Site work for this project consists of clearing and grading for the construction of a new Library
Building. The access to the construction area will be from College Road. The clearing limits are
shown on sheet C 2.0, C 3.0, C 4.0 & C 6.0. Approximately 8 acres of the land will be disturbed
during construction.
The project will impact existing wetlands. The community college has previously reached an
agreement regarding this planned impact, and mitigation has already been completed. NCDENR
Division of Water Quality (DWQ) is currently reviewing the application for this impact. Written
proof of DWQ's approval will be forwarded to the Division of Land Quality as soon as it has been
received.
Stormwater from the new Library project will drain to an existing stormwater pond located north of
College Drive. This pond is owned and maintained by the Town of Smithfield.
PLANNED EROSION AND SEDIMENT CONTROL PRACTICES:
Silt Fence: Silt fence will be utilized to filter sediment-laden runoff in locations where the
drainage area is less than 'A acre per 100-ft of fence.
2. Inlet Protection: Block and gravel inlet protection devices will be installed at new inlets as they
are constructed to filter sediment-laden runoff prior to the runoff entering the storm drainage
system.
3. Construction Entrance: Temporary gravel construction entrances will be utilized to minimize soil
being tracked off the site by construction traffic.
Outlet Protection: Riprap outlet protection aprons will be installed at outlets as they are
constructed to slow storm-water velocities and dissipate energy to protect downstream channels
from erosion.
5. Sediment Skimmer Basins: Sediment skimmer basins will be installed to filter concentrated
sediment laden runoff prior to discharge from the site.
Tree Protection Fencing: Tree protection fencing will be installed to protect existing trees that
are intended to remain. In some locations, silt fence will serve as tree protection fence.
Refer to drawings C4.0 for Construction Sequence and Maintenance Plan & C 7.1-C 7.4 for details.