SW6100601_Calculations_20100610

Wet Pond Calculations
Water Quality Treatment Volume
Volume = 3630 * Rd * Rv * A
Where Rd = 1 inch
Rv = 0.05 + (0.9 * 1)
1 = .478
Ac = 2.14
Volume = 3630 * 1.0 * [0.05 + (0.9 * 0.478)] * 2.14 = 1,587 cf
Surface Area (SA)
SA = DAM 00 * Ratio
DA = Drainage Area = 101,170 sf
Ratio = 2.8 +/-
(based on BUA, average depth, TSS and removal, Table 10-3 for 90% TSS removal, 3 ft average depth,
and 47.8% BUA)
Example
SA = 101,170/100 * 2.8 +l-
SA = 2832 sf +/-
Discharge Rate (cfs) for 2 to 5 days
Discharge Rate (2-5 days) = Water Quality Treatment Vol ume/(seconds/day)/(number of days)
Example (2-5 days)
Discharge Rate (2 days) = 2,832 cf / (86,400 (sec/day) / 2 days = 0.0164 cfs
Discharge Rate (5 days) = 2,832 cf / (86,400 (sec/day) / 5 days = 0.0065 cfs
Orifice Size
Q=CdA[2gHo]A0.5 or A=Q/(Cd((2gHo)A0.5)
A=Q/Cd*(2gHo)A0.5
Where
Q = from 0.0164 to 0.0065 cfs (discharge rate for 2,832 cf in 2 to 5 days)
A=,Q/Cd*(2gHo) A0.5
A= 0.0164 / (0.6 * (2*32.2*(0.91/3)) A 0.5 (2 day draw down) = 0.0062 cfs
A='0.0065 / (0.6 * (2*32.2*(0.91 /3)) A 0.5 (5 day draw down) = 0.0024 cfs
Note: Q must be less than or equal to the pre -development discharge rate for the 1 year 24 hour peak
flow where Q = CIA (0.02 cfs calculated)
D (Diameter Orifice feet) = (4 A / 3.14) A 0.5 = 0.0559 ft
D (Diameter Orifice inches) = 0.0559 ft * 12 inches/feet = from 0.67 inches to 1.0661 inches

LOT 2, AIRPORT COMMERCE PARK
CUMBERLAND COUNTY, NORTH CAROLINA
STORMWATER / EROSION CONTROL NARRATIVE
Prepared for:
FULLBLOCK,LLC
321 NORTH FRONT STREET
WILMINGTON, NC 28401
Prepared by
-DARAMC)t.7NTE
5911 Oleander Drive, Suite 201
Wilmington, NC 28403
Project#10137.PE
June 2010
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35
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LOT 2, AIRPORT COMMERCE PARK
CUMBERLAND COUNTY, NORTH CAROLINA
Project #10137.PE
Table of Contents
Design Narrative
Proposed Improvements
Maintenance
Erosion and Sedimentation Control. Specification
Soils Map
USGS Map
Calculations
Page

LOT 2, AIRPORT COMMERCE PARK
CUMBERLAND COUNTY, NORTH CAROLINA
Project #10137.PE
DESIGN NARRATIVE
Fullblock, LLC proposes to construct a warehouse building at the corner of Airport and
Bridgewood Road within Cumberland County, NC. As a result, please find this design
narrative, plans, and supporting calculations sufficient for the stormwater quality and quantity
control according to NCDENR and Cumberland County regulations. The address of the
property is 115 Airport Road, Fayetteville, NC 28306 with a latitude and longitude of 34' 59' 57"
N, 78' 53' 45" W (Parcel ID# 0435-14-1782; Deed Book 08346 page 0839).
There is currently no existing impervious across the property and the ground cover is mostly
fair open space with a few sparse trees. Soils consist of Wagram-Urban complex (WgB)
according to the provided soils map from NRCS and have a HSG classification of A. According
to the attached USGS map, the project drains to Big Sandy Run which has a stream classification
of C (18-31-25) and is within the Cape Fear River Basin.
PROPOSED IMPROVEMENTS
It is proposed that all runoff resulting from impervious surfaces will be collected by a storm
drainage system and then be conveyed to a wet detention pond where both stormwater quality
and stormwater quantity requirements will be met. The pond has been designed to NCDENR
requirements which include a forebay and a drawdown orifice at permanent pool. Stormwater
from greater storm events will be allowed to exit the wet detention pond by means of a riser
barrel outlet structure and a secondary spillway during emergency situations.
In regard to erosion control, please find that it is proposed to use the wet detention pond as a
sediment basin during construction activities. As a result, please find that we have designed
the sediment basin to NCDENR land quality requirements (per NCDENR Erosion and
Sediment Control Design and Planning Manual (June 1s', 2006)) and have also added a skimmer
to the draw down orifice at permanent pool in order to prevent sediment from leaving the
outlet structure prior to the site being fully stabilized. Other than the sediment basin, it is
proposed to install inlet protection to the storm drain inlets to prevent sediment from entering
the system as well as silt fence and temporary construction entrances along Bridgwood Road.
Please see sheet C-1.0 for all Erosion Control and Sequence of Construction notes. The
sedimentation and erosion control design will commence as depicted in the construction
sequence. Please find all reference material and stormwater / erosion control calculations in the
following pages of this report. Note that some calculations have also been located on the plans
for easy reference during construction.

MAINTENANCE
Contractors shall be responsible for periodic inspection, and maintenance of all indicated
erosion control devices in accordance with the plans and specifications. In addition, inspection
and any necessary maintenance will be required immediately following any significant storm
event. Any erosion control measure that fails to function as intended shall be repaired
immediately. Upon completion of construction and the establishment of stabilized ground
cover, the property owner shall be responsible for any on going site maintenance.

EROSION AND SEDIMENTATION CONTROL SPECIFICATION
PART1-GENERAL
1.1 RELATED DOCUMENT
A. Drawings and general provisions of the Contract, including General .and Supplementary
Conditions and Division 1 Specification Sections, apply to this Section.
1.2 WORK INCLUDED
A. Contractor shall take every reasonable precaution throughout construction to prevent the
erosion of soil and the sedimentation of streams, lakes, reservoirs, other water impoundments,
ground surfaces, or other property as required by State and Local regulations.
B. Contractor shall, upon suspension or completion of land -disturbing activities, provide
protection covering for disturbed areas. Permanent vegetation shall be established at the
earliest practicable time. Temporary and permanent erosion control measures shall be
coordinated to assure economical, effective, and continuous erosion and sediment control
throughout the construction and post construction period.
1.3 RELATED SECTIONS
A. Related Sections — The following Sections contain requirements that relate to this Section:
1. 01011 — Existing Underground Utilities
2. 01015 — Special Conditions for this Contract
3. 01070 -Shop Drawings, Project Data & Samples
4. 02200 — Earthwork, Excavation Trenching, and Backfilling
5. 02230 — Site Clearing
6. 02240 — Dewatering
7. 02485 — Seeding General Areas
1.4 REGULATORY REQUIREMENTS
A. Contractor shall be responsible for -prevention of damage to properties outside the construction
limits from siltation due to,_construction of the project. The Contractor will assume all
responsibilities to the affected property owners for correction of damages that may occur.
Erosion control measures shall be.performed by the Contractor, conforming to the requirements
of, and in accordance with plans approved by applicable state and local agencies and as per the
erosion control portion of the construction drawings and these specifications. The Contractor
shall not allow mud and debris to accumulate in the streets. Should the Contractor pump water
from trenches during construction, appropriate siltation preventative measures shall be taken
prior to discharge of pumped water into any storm drain or stream.

PART2-PRODUCTS
2.1 Open mesh biodegradable mulching cloth. ..
2.2 Fertilizer shall be 10-10-10 grade or equivalent.
2.3 Lime shall be dolomitic agricultural ground 1 limestone containing not less than 10 percent
magnesium oxide.
2.4 Phosphate shall be 20 percent super phosphate or equivalent.
2.5 Provide grass seed mixture as shown on the plans.
2.6 Silt fence shall consist of non -biodegradable filter fabric (Trevira, Mirafi, etc.) wired to
galvanized wire mesh fencing and supported by wood or metal posts.
2.7 NCDOT Class B stone for erosion control.
PART 3 - EXECUTION
3.1 CLEARING
A. , Clearing and grubbing shall be scheduled and performed in such a manner that subsequent
grading operation and erosion control practices can follow immediately thereafter. Excavation,
borrow, and embankment operations will be conducted such that continuous operation. All
construction areas not otherwise protected shall be planted with permanent vegetative cover
within 21 calendar days after completion of active construction.
3.2 STABILIZING
A. The angle for graded slopes and fills shall be no greater than the angle that can be retained by
vegetative cover or other adequate erosion control devices or structures. All disturbed areas not
to be paved and left exposed will, within 21 calendar days of completion of any phase of
grading, be planted or otherwise provided with either temporary or permanent ground cover,
devices, or structures sufficient to restrain erosion.
3.3 REGULATORY REQUIREMENTS
A: Whenever land disturbing activity is undertaken on a tract, a ground cover sufficient to restrain
erosion must be planted or other wise provided within 21 calendar days on that portion of the
'tract upon which further active construction is to being undertaken.
B. If any earthwork is to be suspended for any reason whatsoever for longer than 21 calendar
days, the areas involved shall be seeded with vegetative cover or otherwise protected against
excessive erosion during the suspension period. Suspension of work in any area of operation
does not relieve the Contractor of the responsibility for the control of erosion in that area.

PART 4 - CONSTRUCTION PHASE
4.1 PRACTICES
A. Avoid dumping soil or sediment into any streambed or watercourse. Backfill for stream
crossings shall be placed dry and compacted to minimize siltation of the watercourse, where
applicable.
B. Maintain an undisturbed vegetative buffer where possible between a natural watercourse and
trenching and grading operations.
C. Avoid equipment crossings of streams, creeks, and ditches where practicable.
PART 5 - SEDIMENT CONTROL FEATURES
5.1 GENERAL
A. All devices (silt fences, retention areas, etc.), for sediment control shall be constructed at the
locations indicated prior to beginning excavation on the site. All devices shall be properly
maintained in place until a structure or paving makes the device unnecessary or until directed
to permanently remove the device.
5.2 DESIGN APPLICATIONS
A. Mulch shall be used for temporary stabilization of areas subject to excessive erosion, and for
protection of seed beds after planting where required.
1. Jute, mesh, etc. should be installed as per manufacturer's instructions.
B. Silt fences shall be used at the base of slopes and in drainage swales to restrict movement of
sediment from the site. Straw bales may be required for reinforcement.
C. Riprap shall be used at the proposed outfall pipes as indicated on.plans.
D. Establish vegetative cover on all unpaved areas disturbed by the work.
1. Preparation of Seedbed. Areas to be seeded shall be scarified a depth of 6 inches until a
firm, well -pulverized, uniform seedbed is prepared. Lime, phosphorous, and fertilizer
shall be applied during the scarification process in accordance with the following rates.
a Lime — 2 ton per acre
b. Nitrogen —100 pounds per acre
C. P2O1 — 200 pounds per acre
2. Seeding. Disturbed areas along roads and ditches shall be permanently seeded. with 10-
20 pounds per acre of centipede during the period from March through September.
Seeding performed during the period from April to August shall be temporarily seeded
with 40 pounds per acre of German Millet. The permanent vegetative cover will be over
seeded at the earliest possible time as specified above.
3. Mulch all areas immediately after seeding. Mulch shall be applied and anchored as
specified hereinbefore.

5.3 MAINTENANCE
A. The Contractor shall be responsible for maintaining all temporary and permanent erosion
control measures in functioning order. Temporary structures shall be maintained until such
time as vegetation is firmly established and grassed areas shall be maintained until completion
of the project. Areas which fail to show a suitable stand of grass or which are damaged by
erosion shall be immediately repaired.
5.4 REMOVAL OF SEDIMENT CONTROL DEVICES
A. Near completion of the project, when directed by the Owner's agent, the Contractor shall
dismantle and remove the temporary devices used for sediment control during construction.
All erosion control devices in seeded areas shall be left in place until the grass is established.
Seed areas around devices and mulch after removing or filling temporary control devices.
END OF SECTION 02410

Soil Map —Cumberland County, North Carolina
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USDA Natural Resources Web Soil Survey
adffi Conservation Service National Cooperative Soil Survey
5/3/2010
Page 1 of 3
35' 0 1"
34. 59' 54-

Soil Map —Cumberland County, North Carolina •'(u� w,�.gray)J P , + .,,,�
Map Unit Legend
Cumberland County, North Carolina (NC051)
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
Wgt3 Wagram-Urban land complex, 0 to 8 2.21 100.0 %
percent slopes
Totals for Area of Interest I 2.21 - 100.0%
[:S \ Natural Resources Web Soil Survey - 5/3/2010
® Conservation Service National Cooperative Soil Survey Page 3 of 3

Lot 2, Airport Commerce Park, Fayetteville, NC
NC DENR Retention Requirements
Objective: design a wet detention basin with the following characteristics: a permanent water pool depth between 3- and
6-teet, a surface area that meets TSS removal requirements (values set by NC DENR and included here), a forebay that
is approximately 20% of the total pond volume, a temporary water pool sized to detain the initial 1.0 inch of rainfall runoff, an
outlet device that drains the temporary water pool within 2-5 days, and a length -to -width ratio of approximately 3:1.
Step 1: Determine the surface area required for 90% TSS removal
Post -Development Conditions
Total Drainage Area 2.32 ACRE
Impervious Drainage Area 1.11 ACRE
Impervious Cover 47 8%
Elevation of Permanent Pool Surface
180.50
FT
Average Depth of Permanent Pool
3.00
FT
Elevation of Wet Detention Pond Bottom
176.5
FT
Approximate Pond Length
100
FT
Approximate Pond Width
7G
rr
Value from CAD
Value from CAD
Impervious Cover -(Impervious Drainage
Area)/(Total Drainage Ama)'100%
Value selected by designer
Value from CAD
Value from CAD
Required SAIDA Ratio for 90% TSS Removal 2,890 Value from chart. Reference: '90% TSS
Removal
Required Permanent Pool Surface Area 2,921 SF Required Surface Area=(Required SAIDA
Ratio) *(Total Drainage Area)
Provided Permanent Pool Surface Area 3,770 SF Interpolated value from stage -storage
calculations
Required 1.0" Runoff Volume (Volume of 1-0"Runoff Volume=l inch'Rv'1 foobl2
Temporary Pool) 4,051 CF
inch'(Total Drainage Area)
Total Volume to be Controlled 4.051 CF Total Volume to be Controlled=(Volume Below
Permanent Pool + 1 r. 24hr. Runoff Volume
Storage Elevation at Required Volume 181.41 FT Value is interpolation based upon stage -storage
values. See stage -storage calculations
Step 3: Calculate fhe required /orebay volume (18-22% of total pond volume) and compare to the /orebay volume provided
Total Pond Volume 5.847 CF Value from stage -storage calculations
Required Forebay Volume 1.169 CF P—he"
Provided Forebay Volume:Total Pond Volume 20.6% (Provided Fore
. - Volume)'100%
Step 4: Ved(V that time required to drawdown the 1 04nch runoff volume is within 2 to 5 days.
Diameter of Proposed Low -flow Orifice 1.00 IN Value chosen by designer
Riser Elevation of Outlet Structure
182.00 FT
Value chosen by designer
Total Elevation Head Above Orifice
1.50
(Total Elevation Head Above Onfice)=(Riser
FT
Elevation) -(Elevation of Permanent Pool
Surface)
.
(Average Elevation Head Above
Average Elevation Head Above Orifice
0.50
Odfice)=[(Storage Elevation at Required
FT
Volume)+(Elevation of Permanent Pool
Surface)]r3-(Storage Elevation at Required
Cd, Coefficient of Discharge
0.60
Volume)
Value chosen by designer
Q, Flowrate Through Low -flow Orifice
0.019 CFS
Q=Cd'(Pl)'((Diameterof Orffice)'(1 W12
in ^2/4' '32.2' Ave a Head ^I2
Dmwdown Time for 1.0"Runoff
2.52 DAYS
(Drawdown Time)=(1.0" Runoff Volume)/Q'(1
1$\-'k1 o
11
1000 ` ky
0.
P:\Projecls\Atlanlic Brokerage\10137.PE 115 Airport Road\Documents\Design Calculations\Stormwater\Wel Pond -Airport Road

Lot 2, Airport Commerce Park, Fayetteville, NCB
determine the storage capacity
for Proposed Wet Detention
of the proposed wet detention
Pond side slope above Permanent Pool 3
Veg. shelf 6" above/below Perm. Pool 10 FT
Side Slope below planted shelf 3
incremental and cumulative storage of the wet detention pond per contour interval
Stage/Storage Above Permanent Pool (Including Forebay) -
Cumulative
Contour
Incremental
Volume, S
Contour
Area (SF)
Volume (CF)
(CF)
180.50
3,770
0
0 -Permanent Pool
181.00
5,176
2,237
2,237
182.00
6,096
5,636
7,873
183.00
7,072
6,584
14,457
184.00
8,105
7,589
22,045
Stage/Storage Total Pond
Contour
176.50
177.00
178.00
179.00
180.00
180.50
181.00
182.00
183.00
184.00
Contour
Incremental
Area (SF)
Volume (CF)
357
0
561
230
1,040
801
1,623
2,309
3,770
5,176
6,096
7,072
8,105
1,332
1,966
1,520
2,237
5,636
6,584
7,589
Cumulative
Volume, S
(CF)
0
230
1,030
2,362
4,328
5,847
8,084
13,720
20,304
27,892
Forebay Only (20 % of Total Pond)
Cumulative
Contour Incremental Volume, S
Contour Area (SF) Volume (CF) (CF)
177.00 95 0 0
178.00 198 147 147
179.00 334 266 413
180.00 501 418 830
180.50 988 372 1,202
--Pond Bottom
- Permanent Pool
-Bottom Elev.
- Forebay Volume
P:\ProjectsWtlantic BrokerageM137.PE 115 Airport Road\Documents\Design Calculations\Stormwater\Wet Pond -Airport Road

Project Name: Lot 2, Airport Commerce Pai Client: Atlantic Brokerage pA,RA.Mo a -jam
Project Number: 10137.PE _ _ 1 E
Prepared By: CWM . " '� "' `' ^'
Date: 6/10110
Basin: DA #1 [PRE] Drainage area= 2.32 acres = 0.004 mil
Use
of Basin
Open Space - Fair
2.32 100.0%
Sum: 2.32 100%

Project Name: Lot 2, Airport Commerce Park
Client:
Atlantic Brokerage
Project Number:
10137.PE
Prepared By:
CWM
Date:
6/10/10
PARAMOUINTE
oaDRl: UA 7F1 LPKF=j Drainage area= 2.32 acres = 0.004 mil
of Basin
100.0
0.0
0.0
0.0s.,;.100.0
Land Use % of Basin
'Open Space - Fair
CN A
CN B
CN C
CND
Weighted CN
100.0
49
69
79
84
49M
Impervious 0.0
98
98
98
98
- 0.00
Sum: 100.0
Sum: 49.00
Curve numbers taken from:
TR-55
Use:. 49
= values input by user
= values calculated by spreadsheet

Project Name: Lot 2, Airport Commerce Park
Client: Atlantic Brokerage
Project Number: 10137.PE
Prepared By: CWM
Date: 6/10/10
Basin: DA #1 [PRE] Drainage area=
==Short
Concentration
w
ngth = 550 ft.
1.5 %
er = Short Grass.7) = 0.75 fps12.2 min.
TE — 12.2 min.
PARRNIOUIvTE
2.32 acres = 0.004 MI'
'Use 5 minutes min.

Project Name: Lot 2, Airport Commerce Pai
Client: Atlantic Brokerage JL f V 'TOUNE
Project Number: 10137.PE 1
Prepared By: CWM
Date: 6110/10
Basin: DA #1 [POST] Drainage area= 2.32 acres = 0.004 miz
Area Calculations
d Use
Area Ac.
%of Basin
ervious (Total) =
[Open
1.11
47,6%
Space - Good
1,21
52 2%
Sum:
2.32
100%

Project Name: Lot 2. Airport Commerce Park
Client: Atlantic Brokerage
Project Number: 10antic B
PA RA
M.OUNTE
Prepared By: CWM
Date: 6/10/10
Basin: DA #1 [POST] Drainage area=
2.32 acres =
0.004 miz
Curve Number
C
D Sum0
0.0
0.0100.0Land
Use
Impervious
THSG:A
B CN C
CN D Wei hted CN
8 98
9846.75
Open Space - Good
1 74
8p
20.40
Sum: - :100.0
Sum: 67.14
Curve numbers taken from: TR-55
Use: .-- 67.00
= values input by user
= values calculated by
spreadsheet

Project Name: Lot 2, Airport Commerce Park
Client:
Atlantic Brokerage .
Project Number:
10137.PE
Prepared By:
CWM
Date:
6/10/10
Basin: DA #1 [POST] Drainage area=
U
aw Nc = 1
Ground Cover = Grass / Pav
V (Figure 12.7) = 2 fps
T=.
T= = 5.0 min.
pARAMO UNTE
C N G 1- C C- - 1 N O. , N C.
2.32 acres = 0.004 miz

Hydrograph Summary Redo,Ft „ _.__ __ 1

Hydrograph Summary Rep„oft „ z

Hydrograph Summary Rey„or-t s

4
Hydrograph Summary Rebdraf 000t
yw Hydrographs Extension for AutoCAD®Civil 3DO 2008 by Autodesk Inc v6 052
Hyd.
No.
Hydrograph
type
(origin)
Peak
flow
(cfs)
Time
interval
(min)
Time to
_ peak
(min)
Hyd.
volume
(cuft)
Inflow
hyd(s)
Maximum
elevation
(ry)
Total
strge used
(tuft)
Hydrograph
description
1
SCS Runoff
3.816
1
730
16,137
------
___---
------
PRE
2
SCS Runoff
10.82
1
725
33,357
-----
----
—
POST
3
Reservoir
6.058
1
732
27,521
2
182.44
10,750
WETPOND
i
i
'i
Airport Road.gpw
Return Period: 50 Year
Thursday, Jun 10, 2010

Hydrograph Summary Re�o�rt 5
ydraf ow Hydrographs Extension for AutoCADO Civil 3D® 2008 by Autodesk, Inc, v6.052
!rt
Total Hydrograph
(cfs) min hyd(s) elevation strge used
(ff) description
(cuk)
1 SCS Runoff
5.221 1
730
21,171 ------
2 SCS Runoff
13.21 1
1
725
40,674 ------
3 Reservoir
9.818 1
729
34,837 2
------
------ PRE
—" ------ POST
182.58 11,675 WET POND
Airport Road.gpw I Return Period: 100 Year
Thursday, Jun 10, 2010

4= rs,
Do L
Pipe
Maw mc,
C6"esmay riot bo extrapolated,
Discharge (P/soc)
1ppendi,,c,

"7 Cr? Discharge(03/sec)
Cun•_5 may nn; he ertrapo)atea,
Flpmc 6.066 Dnci6n o; ua9a: probc:an 'uom a: v:ntl ;:., u IbP:t,9, mmnnu:n t;Cl.rvn cm;tl ,icn (T„? 0 5 tliar,lecr).

K
Project Name: Lot 2, Airport Commerce Park
Client:
Atlantic Brokerage
Project Number:
10137.PE
Prepared By:
CWM
Date:
6/4/2010
SEDIMENT BASIN CALCULATIONS
[Designed Per NCDENR Erosion Control Design Manual (6.61
Drainage Area (100 Ac. Max.) = 2.32 Ac.
Q,o, Calcs:
Impervious Area =
1.11 Ac.
Denuded Area =
1.21 Ac.
Impervious Area % of Basin =
47.70
Denuded Area % of Basin =
52.30
rve
Use % of Basin
Sum:
52.31 72
100.0
Curve numbers taken from: TR-55
Tc *= 6.00 min.
* (Pipe Flow from Hydraflow Storm Sewer Analysis)
Qioy.. (From Hydraflow) = 11 cfs
9
pARAMOUNTE
CN B CN C CN D
82 87 89 37.66
Sum:::84.40
Use: 8S

Requirements:
Min. Surface Area (435 sf/cfs) = 4,785 sf
Min. Volume (1,800 cf/Ac.) _ 4,176 cf
Provided:
Basin Volume:
umu a ive
Contour Area
Incremental
Volume
Contour
(SF)
Volume (CF)
(CF)
175.50
77
0
0
176.00
162
60
60
177.00
561
362
421
178.00
1,040
801
1,222
179.00
1,623
1 332
2 553
180.00
2,309
1,966
4,519
180.50
3,770
1520
6,039
181.00
5,176 -
2 237
8 276
182.00
6,096
5,636
13,912
182.25
5,956
1,507
15,418 1
183.00
7,072
4 886
20,304
184.00
8,105
7,589
27,892
Outlet Structure (See Hydraflow Data):
Riser EL. (Principal Spillway)= 182.00
Weir EL. (Emergency Spillway)= 182.25
Proposed Sediment Storage EL. = 181.00
Volume at Proposed EL. = - 8,276 cf
Surface Area at Proposed EL..= 5,176 sf
Pond Dimensions: (@ Principal Spillway
El.)
Length =
100 ft
Width =
38 ft
L to W Ratio =`
3:1
pARAMOUNTE
Skimmer Discharge Elevation
2ser Structure Elevation
mergency Spillway Elevation
Skimmer Design: (SEE ATTACHED FAIRCLOTH SKIMMER SELECTION CHART
*Outflow EL. = 180.50
* = Note that the calculated basin volume for dewatering is the difference in the volumes at
EL. 182.00 and EL. 180.50 and not from the bottom of the basin.
Drawdown Orifice Check
Dewater Vol. =
7,873 cf
Average Head =
0.50 ft ,
Ca =
0.6
D =
1 inches
Toewater =
5 days

Hydrograph Summary Re,�lot
ydoraf ow Hydrographs Extension for AutoCADiN Civil 3D0 2008 by Autodesk, Inc. v6.052
Hyd.
No.
Hydrograph
type
(origin)
Peak
flow
(cfs)
Time
interval
(min)
Time to
peak
(min)
Hyd.
volume
(cuft)
Inflow
hyd(s)
Maximum
elevation
(ft)
Total
strge used
(cuft)
Hydrograph
description
1
SCS Runoff
10.66
1
724
33.450
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SED BASIN
SED BASIN -Airport Road.gpw
Return Period: 10 Year
Friday, Jun 4, 2010

S,,N)b ,�, 1
Z
Determining the Skimmer Size
and the Required_ Orifice
for the
Faircioth Skimmer®Surface Drain
November 2007
Important note: The orifice sizing chart in the Pennsylvania Erosion
Control Manual and reproduced in the North Carolina Design Manual
DOES NOT APPLY to our skimmers. It will give the wrong size orifice
and not specify which size skimmer is required. Please use the
information below to choose the size skimmer required for the basin
volume Provided and determine the orifice size required for the drawdown
time, typically 4-.7 days in Pennsylvania and 3 days in North Carolina.
The size of a Faircloth Skimmer®, for example a 4" skimmer, refers to the maximum diameter of
the skimmer inlet. The inlet on each of the 8 sizes offered can be reduced to adjust the flow rate
by cutting a hole or orifice in a plug using an adjustable cutter (both supplied).
Determining the skimmer size needed and the orifice for that skimmer required to drain the
sediment basin's volume in the required time involves two steps: First, determining the size
skimmer required based on the volume to be drained and the number of days to drain it; and
Second, calculate the orifice size to adjust the flow rate and "customize" the skimmer for the
basin's volume. The second step is not always necessary if the flow rate for the skimmer with
the inlet wide open equals or is close to the flow rate required. for the basin volume and the
drawdown time.
Both the skimmer size and the required orifice radius for the skimmer should be shown for each
basin on the erosion and sediment control plan. Make it clear that the dimension is either the
radius or the diameter. It is also helpful to give the basin volume in case there are questions.
During the skimmer installation the required orifice can be cut in the plastic plug using the
supplied adjustable cutter and installed in the skimmer using the instructions provided.
The plan review and enforcement authority may require the calculations showing that the
skimmer used can drain the basin in the required time.
Determining the Skimmer Size
Step 1. Below are approximate skimmer maximum flow capacities based on typical draw
down requirements, which can vary between States and jurisdictioris and watersheds. If one 6"
skimmer does not provide enough capacity, multiple skimmers can be used to drain the basin.
For drawdown times not shown, multiply the 24-hour figure by the number of days required.
Example: A basin's volume is 29,600 cubic feet and it must be drained in 3 days. A 3" skimmer
with the inlet wide open will work perfectly. (Actually, the chart below gives 29,322 cubic feet but
this is well within the accuracy of the calculations and the basin's constructed volume.)
Example: A basin's volume is 39,000 cubic feet and it must be drained in 3 days. The 3"
skimmer is too small; a 4" skimmer has enough capacity but it is too large, so the inlet will need
November 6, 2007 1

to be reduced using step 2 to adjust the flow rate for the basin's volume. (It needs a 3.2"
diameter orifice.)
1Y:" skimmer: 1,728 cubic feet in 24 hours 6,912. cubic feet in 4 days
S y with a 1 %" head 3,456 cubic feet in 2 days 12,096 cubic feet in 7 days^'
\ 5,184 cubic feet in 3 days
n [2','skimmer:3,283 cubic feet in 24 hours 13,132 cubic feet in 4 days
f�L-� AT (- wth a 2" head � 6,566 cubic feet in 2 day 22,982 cubic feet in 7 days
vOWrnG
�yS9,849 cubic feet in 3 day
-7/$73GF 2%" skimmer: 6,234 cubic feet in 24 hours 24,936 cubic feet in 4 days
with a 2.5" head 12,468 cubic feet in 2 days 43,638 cubic feet in 7 days
Revised 11-6-07 18,702 cubic feet in 3 days
3" skimmer: 9,774 cubic feet in 24 hours 39,096 cubic feet in 4 days
with a 3" head 19,547 cubic feet in 2 days 68,415 cubic feet in 7 days
29,322 cubic feet in 3 days
4" skimmer: 20,109 cubic feet in 24 hours 80,436 cubic feet in 4 days
with a 4" head 40,218 cubic feet in 2 days 140,763 cubic feet in 7 days
Revised 11-6-07 60,327 cubic feet in 3 days
5" skimmer: 32,832 cubic feet in 24 hours 131,328 cubic feet in 4 days
with a 4" head 65,664 cubic feet in 2 days 229,824 cubic feet in 7 days
98,496 cubic feet in 3 days
6" skimmer: 51,840 cubic feet in 24 hours 207,360 cubic feet in 4 days
with a 5" head 103,680 cubic feet in 2 days 362,880 cubic feet in 7 days
155,520 cubic feet in 3 days
8" skimmer: 97,978 cubic feet in 24 hours 391,912 cubic feet in 4 days
with a 6" head 195,956 cubic feet in 2 days 685,846 cubic feet in 7 days
CUSTOM 293,934 cubic feet in 3 days
MADE BY ORDER CALL!
Determining the Orifice
Step 2. To determine the orifice required to reduce the flow rate for the basin's volume and the
number of days to drain the basin, simply use the formula volume factor (from the chart
below) for the same size skimmer. chosen in the first step and the same number of days. This
calculation will give the area of the required orifice. Then calculate the orifice radius using Area
= Tr rZ and solving for r, r = V(Area/3.14) .The supplied cutter can be adjusted to this radius to
cut the orifice in the plug. The instructions with the plug and cutter has a ruler divided into tenths
of inches. Again, this step is not alvvays necessary as explained above.
An alternative method is to use the orifice equation with the head for a particular skimmer
shown on the previous page and determine the orifice needed to give the required flow for the
volume and draw down time. C = 0.59 is used in this chart.
Example: A 4" skimmer is the smallest skimmer that will drain 39,000 cubic feet in 3 days but a
4" inlet will drain the basin too fast (in 1.9 days) To determine the orifice required use the factor
of 4;803 from the chart below for a 4" skimmer and a drawdown time of 3 days. 39,000 cubic
November 6, 2007

feet _ 4,803 = 8.12 square inches of orifice required. Calculate the orifice radius using Area = rz
rZ and solving for r, r = (8.12/3.14) and r = 1.61 ". As a practical matter 1.6" is about as close
as the cutter can be adjusted and the orifice cut..
Factors (in cubic feet of flow per square inch of opening through a round orifice with the head
for that skimmer and for the drawdown times shown) for determining the orifice radius for a
basin's volume to be drained. This quick method works because the orifice is centered and has
a constant head (given above in Step 1).
1'h" skimmer: 960
to drain in 24 hours
3,840
to drain in 4 days
1.920
to drain in 2 days
6,720
to drain in 7 days
2,880
to drain in 3 days
2" skimmer: 1,123
to drain in 24 hours
4,492
to drain in 4 days
2,246
to drain in 2 days
7,861
to drain in 7 days
3,369
to drain in 3 days
2Y:" skimmer:
1,270
to drain in 24 hours
5,080
to drain in 4 days
Revised 11-6-07..
2,540
to drain in 2 days
8,890
to drain in 7 days
3,810
to drain in 3 days
3" skimmer:
1,382
to drain in 24 hours
5,528
to drain in 4 days
2,765
to drain in 2 days
9,677
to drain in 7 days
4,146
to drain in 3 days
4" skimmer:
1,601
to drain in 24 hours
6,404
to drain in 4 days
Revised 11-6-07
3,202
to drain in 2 days
11,207
to drain in 7 days
4,803
to drain in 3 days
5" skimmer:
1,642
to drain in 24 hours
6,568
to drain in 4 days
3,283
to drain in 2 days
11,491
to drain in 7 days
4,926
to drain.in 3 days
6" skimmer: 1,814 to drain in 24 hours 7,256 to drain in 4 days
3,628 to drain in 2 days 12,701 to drain in 7 days
5,442 to drain in 3 days
8" skimmer: 1,987 to drain in 24 hours 7,948 to drain in 4 days.
3,974 to drain in 2 days 13.909 to drain in 7 days
5,961 to drain in 3 days
J. W. Faircloth & Son, Inc.
Post Office Box 757
412-A Buttonwood Drive
Hillsborough, North Carolina 27278
Telephone [phone] FAX [phone]
FairclothSkimmer.com [e-mail]
Orifice sizing Revised 2-2-01: 3-3-05, 2-1-07: 11-6-07
November 6, 2007