SWA000060_(6a)Scanned _10/21/2019

No
PVC TEE
PVC END
CAP
PVC PIPE FLEXIBLE
HOSE
1/2" HOLES IN
UNDERSIDE
ARM ASSEMBLY
MUT101111:11IN0111111
PERSPECTIVE VIEW
NOTE: SKIMMER TO BE TETHERED
00212=11
ORIFICE
PLATE
PVC TEE
[1T 1a 11*1 & &I "I V 9-001
WATER ENTRY
UNIT
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SEE N.C. DENR EROSION and SEDIMENT
CONTROL PLANNING and DESIGN MANUAL
FOR CONDITIONS WHERE PRACTICE APPLIES;
PLANNING CONSIDERATION & DESIGN CRITERIA.
—DESIGN CRITERIA
SUMMARY: SKIMMER SEDIMENT BASIN
PRIMARY SPILLWAY: TRAPEZOIDAL SPILLWAY WITH IMPERMEABLE MEMBRANE
PERSPECTIVE —VIEW
MAXIMUM DRAINAGE AREA: 10 ACRES
FEET PER ACRE OF DISTURBED AREA
0�-
MINIMUM VOLUME: 1800 CUBIC
R-
MINIMUM SURFACE AREA: 325 SQUARE FEET PER CFS OF Q25 PEAK INFLOW
MINIMUM LIW RATIO: 2:1
MAXIMUM L1W RATIO: 6:1
RN
BAFFLE(TYP.)
MINIMUM DEPTH: 2 FEET
DEWATERING MECHANISM: SKIMMER
MINIMUM DEWATERING TIME: 2 DAYS
DESIGN BASIN LIFE: 3 YEARS OR LESS
DAM HEIGHT: 5 FEET MAXIMUM
BAFFLES REQUIRED: is 3 BAFFLES
STABLE TRANSITION
REQUIRED TO THE
BASE OF THE SLOPE
SEE NC EROSION AND SEDIMENT CONTROL
PLANNING AND DESIGN MANUAL,
NOTE: BASINS LESS THAN 20'IN LENGTH MAY
USE 2 BAFFLES.
INLET ZONE 25%
STONE WIFABRIC
OF SURFACE AREA
SKIMMER
FIRST CHA MBER
25% OF SURFACE AREA
SECOND CHAMBER
AMR
25% OF SURFACE AREA
Sediment basin shall be maintained
and silt removed when basin is 1/2 full
EXTEND BAFFLES UP SIDES AS
TO NOT ALLOW FLOW AROUND
THE ENDS.
TETHER
STONE ENERGY OUTLET ZONE 25% OF SURFACE AREA
DISSIPATOR
NOTES:
1. LOCATE SEDIMENT INFLOW TO THE BASIN AWAY
FROM THE DAM TO PREVENT SHORT CIRCUITS
FROM INLETS TO OUTLETS.
2. BASIN MUST BE STABILIZED IMMEDIATELY
UPON CONSTRUCTION AND PRIOR TO SITE
INSPECTION APPROVAL.
SKIMMER SEDIMENT BASIN
BAFFLE DETAIL
SUPPORT ROPE SUPPORT POST
TO WIRE TO 24" INTO BOTTOM
PREVENT SAGGING OR SIDES
STAKE TO
4-MAX SUPPORT WIRE
J.-I
XMIN
COIR MESH OR JUTE, TRENCHED
DESIGN LIFE OF FABRIC INTO BOTTOM AND SIDE
IS 6-12 MONTHS
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. Place temporary sediment control measures below
basin as needed
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. Shape the basin to the specified dimensions. Prevent the skimming device
from settling into the mud by excavating a shallow pit under the skimmer or
providing a low support under the skimmer of stone or timber.
4. Place the barrel (typically 4-inch Schedule 40 PVC pipe) on a firm, smooth
foundation of impervious soil. Do not use pervious material such as sand,
gravel, or crushed stone as backfill around the pipe. Place the fill material
around the pipe spillway in 4-inch layers and compact it under and around
the pipe to at least the same density as the adjacent embankment. Care must
be taken not to raise the pipe from the firm contact with its foundation when
compacting under the pipe haunches.
Place a minimum depth of 2 feet of compacted backfill over the pipe spillway
before crossing it with construction equipment. In no case should the pipe
conduit be installed by cutting a trench through the dam after the embankment
is complete.
5. Assemble the skimmer following the manufacturers instructions, or as
designed.
6. Lay the assembled skimmer on the bottom of the basin with the flexible
joint at the inlet of the barrel pipe. Attach the flexible joint to the barrel pipe
and position the skimmer over the excavated pit or support. Be sure to attach
a rope to the skimmer and anchor it to the side of the basin. This will be used
to pull the skimmer to the side for maintenance.
7. Earthen spillways —Install the spillway in undisturbed soil to the greatest
extent possible. The achievement of planned elevations, grade, design width,
and entrance and exit channel slopes are critical to the successful operation
of the spillway. The spillway should be lined with laminated plastic or
impermeable geotextile fabric. The fabric must be wide and long enough to
cover the bottom and sides and extend onto the top of the dam for anchoring
in a trench. The edges may be secured with 8-inch staples or pins. The fabric
must be long enough to extend down the slope and exit onto stable ground.
The width of the fabric must be one piece, not joined or spliced; otherwise
water can get under the fabric. If the length of the fabric is insufficient for the
entire length of the spillway, multiple sections, spanning the complete width,
may be used. The upper section(s) should. overlap the lower section(s) so
that water cannot flow under the fabric. Secure the upper edge and sides
of the fabric in a trench with staples or pins. (Adapted from "A Manual for
Designing, Installing and Maintaining Skimmer Sediment Basins." February,
1999. J. W. Fairclotb & Son.).
8. Inlets —Discharge 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).
9. trosion controi--uonstruct me structure so mat me aisuiroect area is
minimized. Divert surface water away from bare areas. Complete the
embankment before the area is cleared. Stabilize the emergency spillway
embankment and all other disturbed areas above the crest of the principal
spillway immediately after construction (References: Surface Stabilization).
10. Install porous baffles as specified in Practice 6.65, Porous Baffles.
11. After all the sediment -producing areas have been permanently stabilized,
remove the structure and all the unstable sediment. Smooth the area to
blend with the adjoining areas and stabilize properly (References: Surface
Stabilization).
Maintenance Inspect skimmer sediment basins at least weekly and after each significant
(one-half inch or greater) rainfall event and repair immediately. Remove
sediment and restore the basin to its original dimensions when sediment
accumulates to one-half the height of the first baffle. Pull the skimmer to
one side so that the sediment underneath it can be excavated. Excavate the
sediment from the entire basin, not just around the skimmer or the first cell.
Make sure vegetation growing in. the bottom of the basin does not hold down
the skimmer.
Repair the baffles if they are damaged. Re -anchor the baffles if water is
flowing underneath or around them.
If the skimmer is clogged with trash and there is water in the basin, usually
jerking on the rope will make the skimmer bob up and down and dislodge
the debris and restore flow. If this does not work, pull the skimmer over to
the side of the basin and remove the debris. Also check the orifice inside the
skimmer to see if it is clogged-, if so remove the debris.
If the skimmer arm or barrel pipe is clogged, the orifice can be removed and
the obstruction cleared with a plumber's snake or by flushing with water. Be
sure and replace the orifice before repositioning the skimmer.
Check the fabric lined spillway for damage and make any required repairs
with fabric that spans the full width of the spillway. Check the embankment,
spillways, and outlet for erosion damage, and inspect the embankment for
piping and settlement. Make all necessary repairs immediately. Remove all
trash and other debris from the skimmer and pool areas.
Freezing weather can result in ice forming in the basin. Some special
precautions should be taken in the winter to prevent the skimmer from
plugging with ice.
6 1 I , - W - 1%W&VArm, W
11 _N1 14,11111wilrok
SKIMMER SEDIMENT BASIN
RIP RAP PIPE OUTLET PROTECTION
Pipe Outlet to Flat Area —
No Well-defined Channel J
WIIIIIIIIIyW
WO
Plan
La
. Secti•n AA *VlFilter
blanki'l
Pipe Outlet to Well-defined
Channel
Notes
I - La is the length of the riprap
apron.
2. d = 1.5 times the maximum
stone diameter but not less
than 611.
well-defined channel ex-
tend the apron up the channel
banks to an elevation of 6"
above the maximum tailwater
depth or to the top of the bank,
whichever is less.
4. A filter blanket or filter fabric
should be installed between
the riprap and soil foundation.
Construction l- Ensure that the subgrade for the filter and riprap, follows the required lines
and grades shown in the plan. Compact any fill required in the subgrade to the
Specifications density of the surrounding undisturbed material. Low areas in the subgrade on
undisturbed soil may also be filled by increasing the riprap thickness.
2. The riprap and gravel filter must conform to the specified grading limits
shown on the plans.
3. Filter cloth, when used, must meet design requirements and be properly
protected from punching or tearing during installation. Repair any damage by
removing the riprap and placing another piece of filter cloth over the damaged
area. All connecting Joints should overlap so the top layer is above the
downstream layer a minimum of I foot. If the damage is extensive, replace
the entire filter cloth.
4. Riprap may be placed by equipment, but take care to avoid damaging the
filter.
5. The minimum thickness of the riprap, should be 1.5 times the maximum
stone diameter.
6. Riprap may be field stone or rough quarry stone. It should be hard,
angular, highly weather -resistant and well graded.
7. Construct the apron on zero grade with no overfill at the end. Make the
top of the riprap at the downstream end level with the receiving area or slightly
below it.
8. Ensure that the apron is properly aligned with the receiving stream
and preferably straight throughout its length. If a curve is needed to fit site
conditions, place it in the upper section of the apron.
9. Immediately after construction, stabilize all disturbed areas with vegetation
(Practices 6. 10, Temporary Seeding, and 6.11, Permanent Seeding).
Maintenance Inspect riprap outlet structures weekly and after significant (1/2 inch or greater)
rainfall events to see if any erosion around or below the riprap has taken place,
or if stones have been dislodged. Immediately make all needed repairs to
prevent further damage.
SPECIFICATION AND MAINTENANCE
RIP RAP PIPE OUTSIDE PROTECTION
REFERENCE:
NC EROSION & SEDIUNWRENT CONTROL
PLANNING AND DESIGN MIANUAL
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8/12/2019
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I SHEET -
Sheet 6a
CAD FXE.--
CAMERON
�PROJECT NO.
2019.02