20240122_Specs_Maintenance

PROJECT SPECIFICATIONS AND MAINTENANCE
• Culverts
• Grass Lined Channels
• Rip Rap Lined Channels
• Silt Fences
• Outlet Protection
• Sediment Basin with Rock Check Dam
• Temporary Sediment Trap

Enka Quarry•Mining Permit No. 11-03•Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
Culverts
Culverts will be installed using the open-trench method. The trench will be
excavated to the lines and grades shown in the plans. If the trench bottom contains
unsuitable material, the material will be removed and replaced with an acceptable base
material, such as North Carolina Department of Transportation (NCD07) crusher run
aggregate. Backfill will be placed in uniform lifts not greater than six inches upon
compaction. Fill may be compacted with hand-operated or mechanical tampers. Vibratory
rollers may not be activated until three feet of backfill has been placed and compacted over
the pipe. Rock rip rap protection will be constructed at the culvert inlets and outlets to
prevent erosion by spreading out the flow. All culverts will also include inlet protection in
order to prevent "piping" effect beneath the culvert. Refer to the following diagrams for
typical culvert installation guidelines for corrugated metal pipe (CMP) and concrete pipe.
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NORMAL EARTH FOUNDATION ROCK FOUNDATION AB DIRECTED BY ENGR.
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PLACEMENT OF N I.D.LE NIN. Rr�TS DIRECTED
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r GENERAL NOTES: J 0
D DO NOT OPERATE FI EOUTA OVER ANY PIPE CULVERT UNTIL THE IPE CULVERT HAS C7 0
O I.O.=THE MAXIMUMMAXIMUMHORIZONTAL INSIDE OIHMETER DIMENSION. BEEN PROPERLY SACKFILLED AND NO COVERED WITH AT LEAST S FEET OF APPROVED MATERIAL. Z
0 31 D.D.=THE MAXIMUM HORIZONTAL OUTSIDE DIAMETER DIMENSION. —-—-- SPRINGLINE OF PIPE W W
Z H =THE FILL HEIGHT MEASURED VERTICALLY AT ANY POINT —7 BELECT BACKFILL MATERIAL CLASS III OR CLASS II,TYPE 1
ALONG THE PIPE FROU THE TOP OF THE PIPE TO THE TOP ABOVE AND BELOW SPRINGLINE.
OF THE EMBANKMENT AT THAT POINT.
APPROVED 8UiTAULE LOCAL MATERIAL.
TAKE CARE TO FULLY COMPACT HAUNCH ZONE OF PIPE BACKFILL. M UNDISTURBED EARTH MATERIAL
LOOSELY PLACED SELECT MATERIAL CLASS III OR CLASS II,TYPE 1 WITH ENGINEERING CLASS C OR
VI DIRECTED
FOUNDATION CONDITIONING.ENCAPSULATE
SHEET 1 OF 3 FGR PIPE BEDDING.LEAVE SECTION DIRECTLY BENEATH PIPEOW I R E H SHEET 1 OF 3
D AS PIPE SEATING AND—FILL WILL
.300.01 ncca"PLITSH cBMPACTION. SOD.01

Enka Quarry•Mining Permit No. 11-03•Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
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NORMAL EARTH FOUNDATION ROCK FOUNDATION AS DIRECTED By ExBUNSUITABLE MATERIAL FOUNDATION
PIPE IN TRENCH
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mZ m 8 PLACED NOT LESS THAN B" O.D..2' I, R Q
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N
1 NORMAL EARTH FOUNDATION ROCK FOUNDATION NOR YORE THAN 244
x UNSUITABLE MATERIAL FOUNDATION LL
z PIPE ABOVE GROUND M v
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nT OENEMAL NOTES: DD M"1 T OPERATE EQUIPMENT OVER ANY PIPE CULVERT UNTIL THE CULVERT HAS cJ7 O
O I.D.=THE xnxxxux xoxrzoxrAL IxsroE DIAMETER DiMsuslou. E PROPERLY BACKFIILED AND COVERED WITH AT EAST s OF APv'novsD MATERIAL. z =
OO.D.=THE MAKIMUM HORIZONTAL OUTSIDE DIAMETER DIMENSION. —-—-- SPRINGLINE OF PIPE W W
= HTHE FILL
HEIGHT MEASURED VERTICALLY FR.THE TOP OFPATEANY POINT SELECT
® SELECT BACKFILL MATERIAL CLASS III OR CLASS II,
ALONG THE PIPEOF TXE EMBANKMENT AT THAT
POINT�MF IP TO THE T BELOW SPRINGLINE.
APPROVED SUITABLE LOCAL MATERIAL ABOVE SPRINGLINE.
TAKE CARE TO FULLY COMPACT HAUNCH ZONE OF PIPE BACKFILL. UNDISTURBED EARTH MATERIAL
LOOELYFORMPIPEPBEDDILACEDN6.LEAVE SECTIONC
BE ECT MATERIALCDIRECTLY BENEATHLASS III DR S II PIPE TYPE 1 SELECT MATERIAL CLASS V OR VI FOR FOUNDATION CONDITIONING.ENCAPSULATE
SHEET 2 OF 3 UN COMPACTED AS PIPE SEATING AND BACKFI LL W[LL WITH ENGINEERING FABRIC AS DIRECTED BY THE ENGINEER. SHEET 2 OF 3
300.01 ACWMPLISH COMPACTIGN.o
300.01
vT FLEXIBLE PIPE oy
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y Z Round Corrugated Steel Pine Round Corruaated Aluminum Pipe Q F•QT.
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m z,=D Diameter Minimum cover Maximum Heiaht of Cover/feet) Diameter Minimum cover oMaximum Heiaht of Cover (feet) O O y 2 z
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48 12 48 81 67 113 139 42 12 60 78 96
54 12 54 77 100 123 48 12 52 68 84
60 12 69 90 111 54 12 46 50 74
68 12 81 100 60 12 50 62
72 12 74 91 66 12 51
78 12 81 72 12 41
64 12 69 Z
m o
i m •+FOR DIFFERENT CORRUGATIONS AND ARCH PIPES REFER TO ¢ ~
0 ROADWAY DESIGN MANUAL OR MANUFACTURERS SPECIFICATION. Q
G r J
FT-I y REFER TO THE FOLLOWING FOR PIPE SPECIFICATIONS Z J N
r CSP -AASHTO M36 F J
r y CAA -AASHTO M196 Q N m
2 HOPE - * (Minimum fill) 2'for pipe tliamete rs>_12"and<80" HOPE-AASHTO M294 C
171 M ZZZZ * (Maximum fill) 20'for pipe diameters 5 24" PVC -ASTM F948 or AASHTO M3D4 Z
V v 17'for pipe diameters a So"and s 60"
_ m y ¢ W ~
O PVC ' (Minimum fill) 2'for pipe diameters E:12"and 5 36" NOTES: FILL HEIGHTS SHOWN WERE CALCULATED USING Q d C=3
�„� • (Mezimum fill) 30'for pipe tlismete rs>_12"entl<38" AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS Z N W
Do H D •FILL HEIGHT IS MEASURED FROM THE TOP OF THE PIPE I'MINIMUM COVER FOR ALL SIDE DRAIN PIPE Lj 1 J
r '1` TO THE BOTTOM OF THE PAVEMENT STRUCTURE N ACCORDANCE WITH THE STANDARD SPECIFICATIONS LL J
m a - x O
`� aD RIGID PIPE c LL
C RCP- ' (Minimum fill) 1'fOr Class IV&CLASS V Z 0
M S 2'fOr ClaeB III 8 Clees II REFER TO THE FOLLOWING FOR PIPE SPECIFICATIONS W F
Z • (maximum fill) 10'-Cl&ea II pipe RCP -AASHTO M170 LU
20'-Class III pipe
30'-Class IV pipe
40'-Class V pipe
(For fills>40'&<80'use LRFD Direct DBsign Method) NOTES: FILL HEIGHTS SHOWN WERE CALCULATED USING
AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS
SHEET 3 OF 3 •FILL HEIGHT IS MEASURED FROM THE TOP OF THE PIPE 1'MINIMUM COVER FOR ALL SIDE DRAIN PIPE SHEET 3 OF 3
300.01 TO THE BOTTOM OF THE PAVEMENT STRUCTURE IN ACCORDANCE WITH THE STANDARD SPECIFICATIONS 300.01

Enka Quarry•Mining Permit No. 11-03•Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
Grass Lined Channels
CONSTRUCTION SPECIFICATION
1. Construction will be carried out in such a manner that erosion and
sediment loss will be minimized.
2. Prior to commencing construction, appropriate temporary erosion and
sediment control structures will be installed. Temporary control
structures include (but are not limited to) silt fence, rock check dams
and straw bale barriers.
3. Remove all trees,brush, stumps, and other objectionable material from
the foundation area and dispose of properly.
4. Excavate the channel and shape in line, grade and cross section as
designed, free of irregularities,which impede normal flow.
5. Grade soil away from channel so that surface water may enter freely.
6. Fills shall be compacted as needed to prevent unequal settlement that
could cause damage in the completed diversion.
7. All earth material not needed in construction shall be spread or
disposed of so that it will not interfere with the functioning of the
diversion.
8. Apply lime, fertilizer and seed the channel and adjoining area in
accordance with the Vegetation Plan.
MAINTENANCE
Check grass-lined channels after every substantial rainfall event. It is particularly
important to check the channel outlet and all road crossings for bank stability and evidence
of piping or scour holes. Remove all significant sediment accumulations to maintain the
designed carrying capacity. Keep the grass in a healthy, vigorous condition at all times
since it is the primary erosion protection for the channel. Repairs will be made as soon as
practically possible.
RECLAMATION
Reclamation will be conducted per the Reclamation Plan unless otherwise noted.
Refer to the following drawing of a typical grass-lined conveyance channel.

Enka Quarry•Mining Permit No. 11-03•Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
Vegetated V Ditch
Z Zoo---'
1 d 1
Typical Section Trapezoidal Conveyance Channel (Not to Scale)
b
FB
Z Z
1 1 Ia ID
1 1
b =channel bottom width
d=channel design flow depth
FB =channel freeboard
D =total channel depth
Z=ratio (horizontal:vertical) of channel side slopes
Note: See design plans for specific information related to channel lining

Enka Quarry•Mining Permit No. 11-03•Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
Rip Rap Lined Channels
CONSTRUCTION SPECIFICATION
1. Construction will be carried out in such a manner that erosion and
sediment loss will be minimized.
2. Prior to commencing construction, appropriate temporary erosion and
sediment control structures will be installed. Temporary control
structures include (but are not limited to) silt fence, rock check dams
and straw bale barriers.
3. Remove all trees,brush, stumps, and other objectionable material from
the foundation area and dispose of properly.
4. Excavate the channel foundation and shape in line, grade and cross
section as designed, free of irregularities, which impede normal flow.
Bring over excavated areas to grade by backfilling with moist soil
compacted to the density of the surrounding material.
5. Grade soil away from channel so that surface water may enter freely.
6. Place filter cloth and/or any other bedding material to line and grade as
designed. Place filter and bedding material immediately after slope
preparation. For filter fabrics, overlap the downstream edge by at least
12 inches over the upstream edge that is buried in a minimum 12-inch
trench. Space anchor pins every 3 feet along the overlap. Spread
granular materials in a uniform layer. When more than one gradation
is specified, spread the layers so there is minimal mixing.
7. All earth material not needed in construction shall be spread or
disposed of so that it will not interfere with the functioning of the
diversion.
8. Apply lime, fertilizer and seed the disturbed areas around the channel
in accordance with the Vegetation Plan.
MAINTENANCE
Inspect rip rap lined channels at regular intervals as well as after major rains, and
make repairs as soon as practical. Give special attention to the outlet and inlet sections and
other points where concentrated flow enters. Carefully check stability at road crossings
and look for indications of piping, scour holes or bank failures. Maintain all vegetation
adjacent to the channel in a healthy,vigorous condition to protect the area from erosion and
scour during high flow periods.
RECLAMATION
Reclamation will be conducted per the Reclamation Plan unless otherwise noted.
Refer to the following drawing of a typical riprap-lined conveyance channel.

Enka Quarry•Mining Permit No. 11-03•Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
Typical Rip Rap Conveyance Channel
Z
1 1
w
Filter Fabric

Enka Quarry•Mining Permit No. 11-03•Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
Silt Fences
CONSTRUCTION SPECIFICATIONS
1. Use a synthetic filter fabric or a pervious sheet of polypropylene,nylon,
polyester, or polyethylene yarn, which is certified by the manufacturer
or supplier as conforming to the requirements shown in the following
table.
Specifications for Sediment Fence Fabric
Physical Property Requirements
Filtering Efficiency 85% min.
Tensile Strength at 20% max. Elongation Standard Strength-301b./fin.in. min
Extra Strength 50 lb/lin.in. min
Slurry Flow Rate 1 0.3 al/s ft./min. min
Synthetic filter fabric should contain ultraviolet ray inhibitors and
stabilizers to provide a minimum of six months of expected usable
construction life at a temperature range of 0 to 120' F.
2. Ensure that posts for sediment fences are steel or wooden stakes with a
minimum length of 4 feet. Make sure that steel posts have projections
to facilitate fastening the fabric.
CONSTRUCTION
1. Construct the silt fence barrier of standard strength or extra strength
synthetic filter fabrics.
2. Ensure that the height of the silt fence does not exceed 18 inches above
the ground surface. (Higher fences may impound volumes of water
sufficient to cause failure of the structure).
3. Construct the filter fabric from a continuous roll cut to the length of the
barrier to avoid joints. When joints are necessary, securely fasten the
filter cloth only at a support post with overlap to the next post.
MAINTENANCE
1. Inspect the silt fence at least once a week and after each rainfall. Make
any required repairs immediately.
2. Should the fabric of sediment fence collapse, tear, decompose or
become ineffective, replace it promptly.
3. Remove sediment deposits as necessary to provide adequate storage
volume for the next rain and to reduce pressure on the fence. Take care
to avoid undermining the fence during cleanout.
4. Remove all fencing materials and unstable sediment deposits and bring
the area to grade and stabilize it after the contributing drainage area has
been properly stabilized.

Enka Quarry•Mining Permit No. 11-03 •Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
RECLAMATION
Reclamation will be conducted per the Reclamation Plan unless otherwise noted.
Silt fence is utilized as a temporary measure and shall be removed when the area that drains
into it has been stabilized with permanent seeding. Refer to the following drawing of a
typical silt fence.
CONSTRUCTION OF A SILT FENCE
(WITHOUT WIRE SUPPORT)
1. SET THE STAKES. 2. EXCAVATE A 4"X 4" TRENCH
UPSLOPE ALONG THE LINE OF
STAKES.
6'MAX. /
-� _
FLOW
i
III III �
4.
3. STAPLE FILTER MATERIAL 4. BACKFILL AND COMPACT
TO STAKES AND EXTEND THE EXCAVATED SOIL.
IT INTO THE TRENCH.
Jam/ / � •4��!:•.
FLOW
III = III I•
SHEET FLOW INSTALLATION
(PERSPECTIVE VIEW)
FLOW
A 71 A
B \\
IIII I \\
POINTS A SHOULD BE HIGHER THAN POINT B.
DRAINAGEWAY INSTALLATION
(FRONT ELEVATION)

Enka Quarry•Mining Permit No. 11-03•Permit Modification
Vulcan Construction Materials,LLC•November 14,2023
Outlet Protection
INTRODUCTION
Outlet Protection consists of Class 1 or Class 2 Rip Rap constructed in accordance
with NCDOT standards. Outlet protection for culverts is configured in accordance with
NCDOT design charts. Outlet protection for sediment structures consists of a level area
that varies in size and is designed to accommodate the flows from a particular outlet. Each
Outlet Protection is site specific and a detail is provided for the particular structure to which
the Outlet Protection applies.
The level area consists of NCDOT Class 1 rip rap constructed in accordance with
the plans. Outlet protection is designed to reduce velocity and disperse water. Outlet
protection is designed to reduce the possibility of erosion caused by concentrated waters
on natural slopes.
CONSTRUCTION
1. Clear the foundation area of trees, stumps, roots, loose rock, and other
objectionable material.
2. Excavate the cross section to the lines and grades of the rip rap
placement as shown on the plans. Bring over-excavated areas to grade
by increasing the thickness of the liner or by backfilling with moist soil
compacted to the density of the surrounding material. Place all surplus
excavated material from the trap excavation in the overburden disposal
berm or other approved area.
3. Perform all channel construction to keep erosion and water pollution to
a minimum. Immediately upon completion of the channel, vegetate all
disturbed areas per the approved Reclamation Plan or as stated
otherwise to protect them against soil erosion. Where sediment trap
construction will take longer than 30 days, vegetate incrementally.
MAINTENANCE
1. Inspect outlet protection at regular intervals as well as after major rains,
and make repairs promptly. Give special attention to the outlet and inlet
sections and other points where concentrated flow enters. Carefully
check stability and look for indications of piping, scour holes, or bank
failures. Make repairs immediately. Maintain all vegetation adjacent
to the slope channel in a healthy, vigorous condition to protect the area
from erosion and scour during out-of-bank flow.
RECLAMATION
Reclamation will be conducted per the Reclamation Plan unless otherwise noted.
Refer to the following drawings of a typical outlet protection.

Sediment Basins with Rock Check Dam
Construction Specifications and Maintenance Practice Standards and Specifications
Rock Abutment
-Vkill 5 �I T
X1- Weir Elevation
Class I and II
Riprap '
1' min. NC DOT#5 i
or#57 washed 4
stone ti
' i 4
Min. 1.5' thick
Rock Apron
)Lik *--Cut-off Trench
Filter Fabric
Cross-Section View
Figure 6.63a Rock Dam cross section
Construction 1. Clear the areas under the embankment and strip of roots and other
Specifications
objectionable material. Delay cleaning the reservoir area until the dam is in
place.
2. Cover the foundation area including the abutments with extra-strength filter
fabric before backfilling with rock. If a cutoff trench is required, excavate at
center line of dam,extending all the way up the earth abutments. Apply filter
fabric under the rockfill embankment from the upstream edge of the dam to
the downstream edge of the apron. Overlap fill material a minimum of 1 foot
at all joints,with the upstream strip laid over the downstream strip.
3. Construct the embankment with well-graded rock and gravel to the size
and dimensions shown on the drawings. It is important that rock abutments
be at least 2 feet higher than the spillway crest and at least 1 foot higher than
the dam,all the way to the downstream toe,to prevent scour and erosion at the
abutments.
Rev.6/06 6.63.3

Spillway Details
Figure 6.63b Rock Dam plan view and Top of rock abutment
spillway details
2' min
Slope foundation Spillway
Filter fabric
Natural Ground
0%,
G
facing
�2' min
5_min
- Flow Level apron
k
Spillway crest"
Rock Abutment
4. Sediment-laden water from the construction site should be diverted into
the basin reservoir at the furthest area from the dam.
5. Construct the rock dam before the basin area is cleared to minimize
sediment yield from construction of the basin. Immediately stabilize all
areas disturbed during the construction of the dam except the sediment pool
(References:Surface Stabilization).
6. Safety—Sediment basins should be considered dangerous because they
attract children. Steep side slopes should be avoided. Fences with warning
signs may be needed if trespassing is likely. All state and local requirements
must be followed.
6.63.4 Rev.6/06

Practice Standards and Specifications
Maintenance Check sediment basins after each rainfall.Remove sediment and restore original
volume when sediment accumulates to about one-half the design volume.
Sediment should be placed above the basin and adequately stabilized.
Check the structure for erosion, piping, and rock displacement weekly and
after each significant('/2 inch or greater)rainstorm and repair immediately.
Remove the structure and any unstable sediment immediately after the
construction site has been permanently stabilized. Smooth the basin site to
blend with the surrounding area and stabilize. All water and sediment should
be removed from the basin prior to dam removal. Sediment should be placed
in designated disposal areas and not allowed to flow into streams or drainage
ways during structure removal.
References Surface stabilization
6.10,Temporary Seeding
6.11,Permanent Seeding
6.12,Sodding
6.13,Trees,Shrubs,Vines,and Ground Covers
Sediment Traps and Barriers
6.61,Sediment Basins
6.65,Porous Baffles
North Carolina Department of Transportation
Standard Specifications for Roads and Structures
Rev.6/06 6.63.5

Temporary Sediment Trap
Construction Specifications and Maintenance
Practice Standards and Specifications
6.60
TEMPORARY - . -
Definition A small, temporary ponding basin formed by an embankment or excavation
to capture sediment.
Purpose To detain sediment-laden runoff and trap the sediment to protect receiving
streams,lakes,drainage systems,and protect adjacent property.
Conditions Where Specific criteria for installation of a temporary sediment trap are as follows:
Practice Applies • At the outlets of diversions, channels, slope drains, or other runoff
conveyances that discharge sediment-laden water.
• Below areas that are draining 5 acres or less.
• Where access can be maintained for sediment removal and proper
disposal.
• In the approach to a stormwater inlet located below a disturbed area as
part of an inlet protection system.
• Structure life limited to 2 years.
A temporary sediment trap should not be located in an intermittent or
perennial stream.
Planning Select locations for sediment traps during site evaluation. Note natural
Considerations drainage divides and select trap sites so that runoff from potential sediment-
producing areas can easily be diverted into the traps. Ensure the drainage
areas for each trap does not exceed 5 acres. Install temporary sediment traps
before land disturbing takes place within the drainage area.
Make traps readily accessible for periodic sediment removal and other
necessary maintenance. Plan locations for sediment disposal as part of trap
site selection. Clearly designate all disposal areas on the plans.
In preparing plans for sediment traps,it is important to consider provisions to
protect the embankment from failure from storm runoff that exceeds the design
capacity. Locate bypass outlets so that flow will not damage the embankment.
Direct emergency bypasses to undisturbed natural,stable areas. If a bypass is
not possible and failure would have severe consequences,consider alternative
sites.
Sediment trapping is achieved primarily by settling within a pool formed by
an embankment. The sediment pool may also be formed by excavation,or by
a combination of excavation and embankment. Sediment-trapping efficiency
is a function of surface area and inflow rate(Practice 6.61,Sediment Basin).
Therefore, maximize the surface area in the design. Because porous baffles
improve flow distribution across the basin,high length to width ratios are not
necessary to reduce short-circuiting and to optimize efficiency.
Because well planned sediment traps are key measures to preventing off-
site sedimentation, they should be installed in the first stages of project
development.
Rev.6/06 6.60.1

0
Design Criteria Summary: Temporary Sediment Trap
Primary Spillway: Stone Spillway
Maximum Drainage Area: 5 acres
Minimum Volume: 3600 cubic feet per acre of disturbed area
Minimum Surface Area: 435 square feet per cfs of Q10 peak inflow
Minimum L/W Ratio: 2:1
Minimum Depth: 3.5 feet, 1.5 feet excavated below grade
Maximum Height: Weir elevation 3.5 feet above grade
Dewatering Mechanism: Stone Spillway
Minimum Dewatering Time: N/A
Baffles Required: 3
Storage capacity—Provide a minimum volume of 3600 ft3/acre of disturbed
area draining into the basin. Required storage volume may also be determined
by modeling the soil loss with the Revised Universal Soil Loss Equation or
other acceptable methods. Measure volume to the crest elevation of the stone
spillway outlet.
Trap cleanout—Remove sediment from the trap, and restore the capacity
to original trap dimensions when sediment has accumulated to one-half the
design depth.
Trap efficiency—The following design elements must be provided for
adequate trapping efficiency:
• Provide a surface area of 0.01 acres(435 square feet)per cfs based on the
10-year storm;
• Convey runoff into the basin through stable diversions or temporary slope
drains;
• Locate sediment inflow to the basin away from the dam to prevent short
circuits from inlets to the outlet;
• Provide porous baffles(Practice 6.65,Porous Baffles);
• Excavate 1.5 feet of the depth of the basin below grade, and provide
minimum storage depth of 2 feet above grade.
Embankment—Ensure that embankments for temporary sediment traps do
not exceed 5 feet in height. Measure from the center line of the original ground
surface to the top of the embankment. Keep the crest of the spillway outlet
a minimum of 1.5 feet below the settled top of the embankment. Freeboard
may be added to the embankment height to allow flow through a designated
bypass location. Construct embankments with a minimum top width of 5 feet
and side slopes of 2:1 or flatter. Machine compact embankments.
Excavation—Where sediment pools are formed or enlarged by excavation,
keep side slopes at 2:1 or flatter for safety.
Outlet section—Construct the sediment trap outlet using a stone section of
the embankment located at the low point in the basin. The stone section serves
two purposes: (1)the top section serves as a non-erosive spillway outlet for
flood flows; and (2) the bottom section provides a means of dewatering the
basin between runoff events.
Stone size—Construct the outlet using well-graded stones with a d50 size of 9
inches(Class B erosion control stone is recommended,)and a maximum stone
6.60.2 Rev.6/06

Practice Standards and Specifications
size of 14 inches. The entire upstream face of the rock structure should be
covered with fine gravel(NCDOT#57 or#5 wash stone)a minimum of 1 foot
thick to reduce the drainage rate.
Side slopes—Keep the side slopes of the spillway section at 2:1 or flatter.
To protect the embankment,keep the sides of the spillway at least 21 inches
thick.
Depth—The basin should be excavated 1.5 feet below grade.
Stone spillway height—The sediment storage depth should be a minimum of
2 feet and a maximum of 3.5 feet above grade.
Protection from piping—Place filter cloth on the foundation below the riprap
to prevent piping. An alternative would be to excavate a keyway trench across
the riprap foundation and up the sides to the height of the dam.
Weir length and depth—Keep the spillway weir at least 4 feet long and sized
to pass the peak discharge of the 10-year storm(Figure 6.60a). A maximum
flow depth of six inches, a minimum freeboard of 1 foot, and maximum side
slopes of 2:1 are recommended. Weir length may be selected from Table 6.60a
shown for most site locations in North Carolina.
Cross-Section 12" min. of NCDOT#5 �_m n
or#57 washed stone -
T �-1-\-- - ---------- ----
1.5' min.
3600 cu ft/acre w L V
max
tit min filter
fabric
Design settled 1' Overfill 6" for
p min. settlement
Plan View
t 9� Emergency by-
+ ttis 4' k; ti y�oQ pass 6" below
---- ------ ------ 5 ---------- �� min. ��,:� settled
top of
Q
T- max pti
I fill � �''� dam
2 to 3.5' •;�� ,,, by
Natural
3 Ground
filter
fabric min.
Figure 6.60a Plan view and cross-section view of a temporary sediment trap.
Rev.6/06 6.60.3

Table 6.60a Drainage Area Weir Length'
Design of Spillways (acres) (ft)
1 4.0
2 6.0
3 8.0
4 10.0
5 12.0
' Dimensions shown are minimum.
Construction 1. Clear,grub,and strip the area under the embankment of all vegetation and
Specifications root mat. Remove all surface soil containing high amounts of organic matter,
and stockpile or dispose of it properly. Haul all objectionable material to the
designated disposal area.
2. Ensure that fill material for the embankment is free of roots, woody
vegetation, organic matter, and other objectionable material. Place the fill in
lifts not to exceed 9 inches,and machine compact it. Over fill the embankment
6 inches to allow for settlement.
3. Construct the outlet section in the embankment. Protect the connection
between the riprap and the soil from piping by using filter fabric or a keyway
cutoff trench between the riprap structure and soil.
• Place the filter fabric between the riprap and the soil. Extend the fabric
across the spillway foundation and sides to the top of the dam;or
• Excavate a keyway trench along the center line of the spillway foundation
extending up the sides to the height of the dam. The trench should be at
least 2 feet deep and 2 feet wide with 1:1 side slopes.
4. Clear the pond area below the elevation of the crest of the spillway to
facilitate sediment cleanout.
5. All cut and fill slopes should be 2:1 or flatter.
6. Ensure that the stone (drainage) section of the embankment has a
minimum bottom width of 3 feet and maximum side slopes of 1:1 that extend
to the bottom of the spillway section.
7. Construct the minimum finished stone spillway bottom width, as shown
on the plans, with 2:1 side slopes extending to the top of the over filled
embankment. Keep the thickness of the sides of the spillway outlet structure
at a minimum of 21 inches. The weir must be level and constructed to
grade to assure design capacity.
8. Material used in the stone section should be a well-graded mixture of stone
with a d50 size of 9 inches(class B erosion control stone is recommended)and
a maximum stone size of 14 inches. The stone may be machine placed and the
smaller stones worked into the voids of the larger stones. The stone should be
hard,angular,and highly weather-resistant.
9. Discharge inlet water into the basin in a manner to prevent erosion. Use
temporary slope drains or diversions with outlet protection to divert sediment-
laden water to the upper end of the pool area to improve basin trap efficiency
(References:Runoff Control Measures and Outlet Protection).
6.60.4 Rev.6/06

Practice Standards and Specifications
10. Ensure that the stone spillway outlet section extends downstream past the
toe of the embankment until stable conditions are reached and outlet velocity
is acceptable for the receiving stream. Keep the edges of the stone outlet
section flush with the surrounding ground,and shape the center to confine the
outflow stream(References: Outlet Protection).
11. Direct emergency bypass to natural, stable areas. Locate bypass outlets
so that flow will not damage the embankment.
12. Stabilize the embankment and all disturbed areas above the sediment pool
and downstream from the trap immediately after construction (References:
Surface Stabilization).
13. Show the distance from the top of the spillway to the sediment cleanout
level(1/2 the design depth)on the plans and mark it in the field.
14. Install porous baffles as specified in Practice 6.65,Porous Baffles.
Maintenance Inspect temporary sediment traps at least weekly and after each significant('/2
inch or greater)rainfall event and repair immediately. Remove sediment,and
restore the trap to its original dimensions when the sediment has accumulated
to one-half the design depth of the trap. Place the sediment that is removed in
the designated disposal area, and replace the part of the gravel facing that is
impaired by sediment.
Check the structure for damage from erosion or piping. Periodically check the
depth of the spillway to ensure it is a minimum of 1.5 feet below the low point
of the embankment. Immediately fill any settlement of the embankment to
slightly above design grade. Any riprap displaced from the spillway must
be replaced immediately.
After all sediment-producing areas have been permanently stabilized,remove
the structure and all unstable sediment. Smooth the area to blend with the
adjoining areas,and stabilize properly(References:Surface Stabilization).
References Outlet Protection
6.41,Outlet Stabilization Structure
Runoff Control Measures
6.20,Temporary Diversions
6.21,Permanent Diversions
6.22,Diversion Dike(Perimeter Protection)
6.23,Right-of-way Diversion(Water Bars)
Surface Stabilization
6.10,Temporary Seeding
6.11,Permanent Seeding
6.15,Riprap
Sediment Traps and Barriers
6.61,Sediment Basins
6.64,Skimmer Basins
6.65,Porous Baffles
North Carolina Department of Transportation
Standard Specifications for Roads and Structures
Rev.6/06 6.60.5