SW8050301_UNKNOWN_20050309

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
❑ COMPLIANCE EVALUATION INSPECTION
DOC DATE
15Z2'�,30 2
YYYYMMDD

Permit No. 'W � 0 �-U3 D %
(to be provided by DWQ)
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
T his form may be photocopied for use as an original
DWO Stormwater Management Plan Review:
A complete stormwater management plan submittal includes a wet detention basin supplement for each basin,
design calculations, plans and specifications showing all basin and outlet structure details, and a signed and
notarized operation and maintenance agreement.
L PROJECT INFORMATION (please complete the following information):
Project Name: Willis Stora e
Contact Person: __Phillip Tripe Phone Number: 910 7635100
For projects with multiple basins, specify which basin this worksheet applies to: 1
elevations
Basin Bottom Elevation 19.0 ft.
Permanent Pool Elevation 25.0 ft
Temporary Pool Elevation 27.0 ft
areas
Permanent Pool Surface Area 14,027 sq.ft.
Drainage Area
Impervious Area
volumes
Permanent Pool Volume
Temporary Pool Volume
Forebay Volume
Other parameters
SA/DA'
Diameter of Orifice
Design Rainfall
Design TSS Removal2
5.4 ac.
3.38 ac.
(floor of the basin)
(elevation of the orifice)
(elevation of the discharge structure overflow)
(water surface area at the orifice elevation)
(on -site and of -site drainage to the basin)
(on -site and off -site drainage to the basin)
48,810 cu.ft. (combined volume of main basin and forebay)
33.026� cu.ft. (volume detained above the permanent poop
9_�____663 cu.ft. (approximately 20% of total volume)
3.97
1.25 in.
1.0 in.
90� T %
(surface area to drainage area ratio from DWQ table)
(2 to 5 day temporary pool draw -down required)
(minimum 85% required)

i

Footnotes:
I. When using the Division SAIDA tables, the correct SA/DA ratio for permanent pool sizing should be computed based upon the
actual impervious % and permanent pool depth. Linear interpolation should be employed to determine the correct value for non-
standard table entries.
2. In the 20 coastal counties, the requirement for a vegetative filter maybe waived if the wet detention basin is designed to provide
90% TSS removal. The NCDENR BMP manual provides design tables for both 85% TSS removal and 90% TSS removal.
II. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices Manual
(N.C. Department of Environment, Health and Natural Resources, February 1999) and Administrative Code
Section: 15 A NCAC 2H .1008.
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the agent may initial below. If a requirement has not been met, attach justification.
Applicants Initials
a. The permanent pool depth is between 3 and 6 feet (required minimum of 3 feet).
b. The forebay volume is approximately equal to 20% of the total basin volume.
c. The temporary pool controls runoff from the design storm event.
d. The temporary pool draws down in 2 to 5 days.
�- c. If required, a 30-foot vegetative filter is provided at the outlet (include non -erosive flow
calculations).
f. The basin length to width ratio is greater than 3:1.
g. The basin side slopes above the permanent pool are no steeper than 3: 1.
;;Eel ^ h. A submerged and vegetated perimeter shelf with a slope of 6:1 or less (show detail).
i. Vegetative cover above the permanent pool elevation is specified.
j. A trash rack or similar device is provided for both the overflow and orifice.
k. A recorded drainage easement is provided for each basin including access to nearest right-
of-way.
1. If the basin is used for sediment and erosion control during construction, clean out of the
basin is specified to be performed prior to use as a wet detention basin
llfl� M. A mechanism is specified which will drain the basin for maintenance or an emergency.
III. WET DETENTION BASIN OPERATION AND MAINTENANCE AGREEMENT
The wet detention basin system is defined as the wet detention basin, pretreatment including forebays and the
vegetated filter if one is provided.
This system (check one) ❑ does X does not incorporate a vegetated filter at the outlet.
This system (check one) 0 does X does not incorporate pretreatment other than a forebay.

Maintenance activities shall be performed as follows:
After every significant runoff producing rainfall event and at least monthly:
a. Inspect the wet detention system for sediment accumulation, erosion, trash accumulation,
vegetated cover, and general condition.
b. Check and clear the orifice of any obstructions such that drawdown of the temporary pool occurs
within 2 to 5 days as designed.
2. Repair eroded areas immediately, re -seed as necessary to maintain good vegetative cover, mow vegetative
cover to maintain a maximum height of six inches, and remove trash as needed.
3. Inspect and repair the collection system (i.e. catch basins, piping, swales, riprap, etc.) quarterly to
maintain proper functioning.
4. Remove accumulated sediment from the wet detention basin system semi-annually or when depth is
reduced to 75% of the original design depth (see diagram below). Removed sediment shall be disposed
of in an appropriate manner and shall not be handled in a manner that will adversely impact water quality
(i.e. stockpiling near a wet detention basin or stream, etc.).
The measuring device used to determine the sediment elevation shall be such that it will give an accurate
depth reading and not readily penetrate into accumulated sediments.
When the permanent pool depth reads 4.5 feet in the main pond, the sediment shall be removed.
When the permanent pool depth reads 2.25 feet in the forebay, the sediment shall be removed.
BASIN DIAGRAM
ill in the blanks)
Permanent Pool Elevation 25.0
Sediment moval El. 22.75 75 0
_ - _ _ _ _ _ - - - . Sediment Removal Elevation 20.5 75%
Bottom evation22.0 %-------------------------------------------- ----
FOREBAY
Bottom Elevation 19.0
MAIN POND
Remove cattails and other indigenous wetland plants when they cover 50% of the basin surface. These
plants shall be encouraged to grow along the vegetated shelf and forebay berm.
6. If the basin must be drained for an emergency or to perform maintenance, the flushing of sediment
through the emergency drain shall be minimized to the maximum extent possible.

7. All components of the wet detention basin system shall be maintained in good working order.
I acknowledge and agree by my signature below that I am responsible for the performance of the seven
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to any
changes to the system or responsible party.
Print name: Al Willis
Title: President
Address: 5296 Main Street, Shallotte, NC 28459�
Phone:
Signatu
Date: 1�7 ` C1.9 - e .f!
Note: The legally responsible party should not be a homeowners association unless more than 50% of the lots have been sold and
a resident of the subdivision has been named the president.
I, ( a Notary Public for the State of North Carolina , County of
do hereby certify that -A] Willis personally
appeared before me this �� day of F r 2005 , and acknowledge the due execution of the
forgoing wet detention basin maintenance requirements. Witness my hand and official seal,
\\`ONti u t r r r rU!!!i/ �?
4
E`' PUBL�G
yoFq 'CO
`
!!llrlrr114ti��tiO
SEAL
My commission expires

2/2812005
MVL
Willis Storage
Stormwater Calculations
03116
Total Draina e Area
s . ft.
acres
235,159
5.40
Impervious Area
Land Use
sq. ft.
acres
building
50,475
1.16
asphalt
71,967
1,65
concrete
1,050
0.02
road
23,926
0.55
Total
147,418
3.38
Stormwater Calculations:
Time of Concentration:
Hydraulic Length (L) = 600 ft.
hange in Height (H) = 9 ft.
Tc = (L' /H).'"b / 128
- 5.42 min,
Flow for 10 year, 6 hour Storm (Q10)
QPRE - (CARE) x (110) x (Area)
= 8.50 cfs
QPOST - (CPOST) x (110) x (Area)
= 23.47 cfs
Detention Pond Design'.
Pond Size:
Elevation
ft.)
Surface Area
(sq. ft.)
Normal Pool
25.00
14,027
Flood Pool
27.00
18,999
Top of Bank
28.50
23,036
Bottom of Poof
19.00
2,243
Total Provided Storage Volume:
Vol. _ [(Normal pool SA + Flood Pool SA) / 2)
x (F.P. elev. - N.P. elev.)
= 33,026 cu. ft.
% impervious = 0.627
= 62.7%
say 63.0%
CPRE = 0,25
CPosT = (% imp.)(.95)+(1-% imp.)(.25)
0.69
110 = 6.30 in/hr
Ie0 = 7.79 in/hr
Flcw for 50 year, 6 hour Storm (Q50);
QPRE _ (CPRE) x (fi10) x (Area)
= 10.51 cfs
QPosT = (CQosr) x (110) x (Area)
29.02 cfs
z>mie aurace Hrea requirement at normal pool
Pond side slopes = 3 :1
Depth below N.P. = 6 ft.
SA/DA = 0.0397
(Chart for 90% TSS Removal for Wet Detention
Pond without Vegetative Filter)
Required SA = (SA/DA) x (Total Drainage Area)
9,336 sq. ft.
State Volume Reauirement for Storaae of first 1" runoff:
Rv = .05+.009(Percent Impervious)
= 0.6141976 in/in
,t%;`CA' _ (Des1g2n0 e cu.t)ftRv)(Drainage Area)
SEAL r w
r r
10
17374
ova
RE
03116_POND
1 of 2

2/28/2005
MVL
Pond Volume:
Willis Storage
Stormwater Calculations
Bottom SA = 2,243 sq. ft.
Normal Pool SA = 14,027 sq, ft.
Vol. = [(N.P. SA + Bottom SA) 12] x (N,P. el. - Bottom el.)
48,810 cu, ft.
Forebay:
Required Volume
Voi. = 20% of storage volume
- 9.762 cu. ft.
Provided Volume
Bottom SA = 21287 sq. ft,
Normal Pool SA = 4,155 sq. ft.
Vol. = [(N.P. SA + Bottom SA) 12] x (N.P. el. - Bottom ei.)
= 9,663 cu. ft.
depth = 3 ft.
Outlet Structure Design:
Flow for 2-day drawdown:
for 1st 1" of stormwater,
Q = Required Vol. 1 172,800 sec. (2-days)
= 0.070 cfs
ne uirea Hrea or ripe ror z-aay arawaown:
A= Q I [Cd x SQRT(2 x g x h)]
Cd = 0.6
g = 32.2 ft.ls2
h = (F.P. elev.- N,P. elev.) 12
A = 0.0145 sq. ft.
Diameter of Pipe for 2-dav drawdown;
DIA. = SQRT[(A x 4) 1 pi]
= 0.1357 ft.
1.63 in.
Use 1.25" orifice
Outlet Structure Check:
Using a 4' x 4' Basin,
Perimeter (L = 16 ft.
Q = CIA
C = (% imp.)(.95) + (1-% imp.)(.25)
0.69
1 = 6.30 in. for a 10 yr. Storm
A = 5.40 Acres
23.47 cfs
Flow for 5-day drawdown:
for 1st 1" of stormwater,
Q = Required Vol. / 432,000 sec. (5-days)
= &C28 cfs
Kegwea ,Area or ripe Tor o-aay arawaown:
A= 0I[CdxSQRT(2xgxh)]
Cd = 0 6
g = 32.2 ft./s2
h = (F.P. elev. - N.P elev.)12
A = 0,0058 sq. ft.
Diameter of Pipe for 5-day drawdown:
DIA. = SQRT[(A x 4) / pi}
0.0858 ft.
1.03 in.
Q= CwxLXH1
H = [Q 1 (Cw x L)]213
Cw = 3
0.62 ft.
Peak elevation = flood pool elevation + H
27.62 ft.
03116
03116_POND 2 of 2

02/24/05
Stormwater Narrative
Willis Storage
Brunswick County, NC
TE03116
Willis Storage is a 5.40-acre existing vacant tract proposed for commercial storage buildings.
Impervious areas include 50,475 sf of building, 1,050 sf of sidewalk and 95,893 sf of asphalt.
The total percent impervious is 63.0%.
The project will be treated by wet detention. The detention pond will be designed to meet the
State's 1" and the County's 10-year pre -post requirement. Outflow from the pond drains to the
Shallotte River, classification SC HQW.

.'>�, ... , .. ;''f• {}!, .. :!, ;,• it .�! . �. ' ,f. `��: .. .. � ..� .t.' .. ,...
,tl. .. �:..."y. .. .d! ... is f1 '3'. �i t �,. "lr'; .,'• I •�• `i;. � :i.. ... � .

DETENTION POND ANALYSIS FILE NAME: 050301-1
PROJECT SW8 050301 REVIEWER- P.Bartlett
PROJECT NAME: Willis Storage
DATE:
01-Mar-05
Receiving Stream:
Shallotte River
Class:
C;Sw, HQW
Drainage Basin:
Lumber River
Index No.
15-25-2-(1)
Site Area
5.40 acres
Drainage Area
:" 3 !
square feet
Area =
5.40 acres
IMPERVIOUS AREAS
Rational C
buildings
50475.00
square feet
0.95
streets
23926-00
square feet
0.95
parking
71967.00
square feet
0.95
sidewalks
1050.00
square feet
0.95
square feet
square feet
TOTAL
square feet
Rational Cc= 0.67
SURFACE AREA CALCULATION
% IMPERVIOUS 62.69%
Des. Depth 6
TSS: 90
SA/DA Ratio 3.53%
Req. SA 8312 sf
Prov. SA Q277: sf
VOLUME CALCULATION * place a "ll" in the box if Rational is used
Rational ?*
Des. Storm
iQt inches
Rv=
0.61
Bottom
19 msl
Perm. Pooli
MSI
Design Pool
27 msl
Design SA
18999 sf
Req. Volume
>13133 cf
Prov. Volume
3Q2 cf
ORIFICE CALCULATION
Avg. Head =
Flow Q2, cfs
Flow Q5, cfs
No. of Orifices
Diameter, inches
Drawdown =
FOREBAY
Perm. Pool Volume
Req. Forebay Volume=
Provided Volume=
Percent=
SA @
Elevation=
Q2 Area =
Q5 Area =
Orifice Area
Q=
in
COMMENTS
Surface Area , Volume and Orifice are within Design Guideline:
48810
9762
9663.00
2.30 sq. in.
0.92 sq. in.
1.23 sq. in.
0.040 cfs
x F777
r,
'A