SW8121017_COMPLIANCE_20121031

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW vA& r7
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
.2v/a`o3/
YYYYMMDD

WET DETENTION POND ANALYSIS - ALL RULES
FILE NAME: S:1WQSISTORMWATERIEXCELSPREADSHEETSIPOND1121017
PROJECT #: SW8 1121017 REVIEWER: jcsb- �-
Initial Run Date October 31, 20_
PROJECT NAME: Onslow County Government Center Last modified _ 31-Oct-12
Receiving Stream
Drainage Basin:
New River Class: r r
Ll&hite Oak Within 112 mile SA? Ln
Index No. fi
Site Area 7,63 acres
ODrainage Area 332363.00 square feet DA Area 7.63 acres
Rules- "2008" or "Ph2" _
IMPERVIOUS AREAS - BUA Runoff C
Buildings 56412.00 square feet 1
Parking 164493.00 square feet 0,98
SW 8193.00 square feet 0.95
Future square feet 0.95
Offsite square feet 0.95
Other 9512.00 square feet 0.95
'BUA at diff. D_ S(D square feet 0.95
TOTAL 238610.00 square feet
SURFACE AREA CALCULATION (with added DA and BUA at different design storm)
Overall % Impervious 71.79% SAIDA Ratio 8.33%
Average Design Depth 3 feet Req. SA 27696 sf
TSS, 85 or 90: 90 % Prov. SA 2BO13 sf
TEMPORARY POOL AND FOREBAY VOLUME CALCULATIONS
New BUA Old BUA
Drainage Area(D 332363.00 sf
BUA 238610.00 0.00 sf
Post development Rv= 0.696 #DIV/0! unitless
Old BUA Design Storm
inches
Old BUA Design Volume
0
1.5" New BUA Design Storm Volume
28921
1 yr. 24 hour precipitation depth (inches)
350
from NOAA chart
Predevelopment Rv value
0.05
Use 0.05 if no existing BUA
1 yr. 24 hr. Pre -development volume
4847
Icubic feet
1 yr. 24 hr. Post -development volume
67482
cubic feet
2008 Design Volume
28921
cubic feet
Phase 2 Design Volume
28921
cubic feet
Required Volume
Top of Sediment
Bottom of5helf
Permanent Pool
Top of Shelf
Temporary Pool
Volume met at elev
Vol. Prov. at TP
28921
26.00
28.50
29.00
29.50
30.00
30.73
31898.00
jcf
msl .........
msl..........
msl.........
msl..........
msl.........
msl
cf
Area, sf
Inc. volume
Acc. volume
22626.00
0.00
0.00
22626.00
56565.00
56565.00
28013.00
12659.75
69224.75
32711.00
15181.00
84405.75
34157.00
16717.00
101122.75
FORESAY
Perm. Pool Volume=
Req. Forebay Volume=
Provided Volume=
Percent=
Max Pump HP
69225
13845
0.0%
Calculated Average Depth, feet= 12.95
114
ORIFICE CALCULATION
Average Head
Flow 02, cfs
Flow 05, cfs
No. of Orifices
Diameter, inches
Drawdown =
I yr 24 hr intensity, in/hr
Runoff Coefficient
1 yr 24 hr peak Q
Orifice flow<1y24hr ?
feet
cfs
cfs
or weir H x W
days
NOAA chart @t
unitless
cfs
02 Area = 9,06
Q5 Area = 3.62
Orifice Area = 3.14
Av . Flow Q= 0,058
in x
'# of end contractions, N =
discharge coefficient, C =
Effective weir length, L
sq. inches
sq. inches
sq. inches
cfs
3.31
0.31
0.167
0.067
1
2.00
5.8
0.50
0.78
2.96
YES -OK

N&WK
WDICKSON
community infrastructure consultants
October •z6; 2Q1.2
Mr. Chris Baker
NCDENR
Division of Water Quality — Wilmington Regional Office
127 Cardinal Drive Extension
Wilmington, North Carolina 28405
RE: NCDENR Stormwater Permit
Onslow County Government Center
Onslow County
WKD Project Number 20120084.00.WL
Dear Mr. Baker:
On behalf of Onslow County, we are pleased to submit for your review and approval through the Express
Review Program the following information for the subject project:
1 . Original and one copy of the Application Form SWU-101;
2. Original and one copy of the Stormwater Narrative;
3. Original and one copy of the Wet Detention Basin Supplement;
4. Original and one copy of the Wet Detention Basin O+M Agreement;
5. Original and one copy of the Deed Information;
6. Original and one copy of the Jurisdictional Determination;
7. Original and one copy of the USGS Map with Project Site;
8. Original and one copy of the Stormwater and Erosion Control Calculations;
9. Original and one copy of the Geotechnical Report with SHWT Determination;
10. Two sets of project plans.
11. Check for $4,000 made out to NCDENR for application fee.
Thank you for your attention to this matter. If you have any questions, please contact me at [phone]
or [e-mail].
Sincerely,
W. K. Dickson Co., Inc.
6tm
Denise Freund, PE
Project Manager
Enclosures
CC Jeffrey L. Hudson, Onslow County Manager
909 Market Street
Wilmington, NC 28401
Tel: 910,762.4200
Fax: [phone]
www.wkdickson.com
RIECF
OCT 2 6 Z01Z
BY:
Transportation . Water Resources . Urban Development . Geomatics

►..
STORMWATER NARRATIVE
Onslow County Government Center
for
Onslow County, North Carolina
October 2012
026597 =
W. K. Dickson & Co., Inc.
909 Market Street
Wilmington, North Carolina 28401
[phone]
E
201Z� Y.

The primary intent of the Onslow County Government Center project is the consolidation
of the Onslow County Government offices. Currently, Onslow County government offices
are distributed at numerous locations throughout both Onslow County and the City of
Jacksonville. The Onslow County Government Center is proposed to be constructed on Lot
15 in Burton Business and Industrial Park just north of Jacksonville, NC in Onslow County.
The total area of the project site is 13.48 acres. The total area for the project Limits of
Disturbance is 9.95 acres (443,051 SF).
The currently undeveloped project site is located in the White Oak River Basin and drains'
via sheet flow and channelized flow to the New River, Stream Index (19-1), which is
classified C; NSW. The project will be high density with proposed improvements to
include the Onslow County Government Center, a storage building, associated parking,
and related improvements.
There are two existing stormwater detention basins on the project site that were constructed
with the roadway network for Burton Business and Industrial Park. The stormwater
detention basins were permitted by NCDENR under Permit No. SW8 990854. The
impervious areas associated with this project are not conveyed to the existing stormwater
detention basins, but to a new wet detention basin designed for the impervious area
associated with the Onslow County Government Center. No modifications are proposed to
the existing stormwater detention basins.
The proposed wet detention basin has been sized to account for all of the proposed
impervious area associated with the project with a design rainfall depth of 1.5 inches. The
total drainage area to the stormwater pond is approximately 7.63 acres. The impervious
area that will be conveyed to the stormwater pond via the proposed underground
stormwater drainage system consists of 56,412 ft2 of buildings, 164,493 ft' of parking,
8,193 ft2 of sidewalks, and 9,512 ftz of other on -site for a total impervious area of 238,610
ft2. All roof drainage will be conveyed to the underground stormwater drainage system.
Due to site constraints, retaining walls are proposed at several locations around the
perimeter of the pond. Retaining walls are also proposed within the stormwater pond itself
in order to reduce the footprint of the proposed basin.
There are no wetland impacts associated with the project.
FI]D
OCT. 2 6 2012
:sY:

CO- salting Engineers - hand Surveyors - Land Planners
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onslow Cmnty
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OCT 2 6 2012
1BY:
BOUNDARY & DIVISION MAP
LOT
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UNNAMED TRIBUTARY
TO THE NEW RIVER
GRAPHIC SCALE 2
NEW RIVER
(,000 500 0 500 1,000 2,000 .-3 , I - . ,• v-C�1-3
(IN FEET) OCT 2 6 2012
-N-
SCALE- I " = 1 ,000' BY:
5C9 MARKET 5TRF.fr Date : 8l8/ 12
DWK WILMiNGTON, NC 28401
(9
i o) 7E2-4200 Scale: I • = I ,ODo' USGS TOPOGRAPHIC QUADRANGLE
DICKSON Office L° tlo°" Noro Card— Drawn: JRR ONS'LOW COUNTY GOVERNMENT CENTER
so.tn C.-hra Chk: DLF LOT 15 — BURTON INDUSTRIAL PARK
community infrastructure consultonts G1�9'a
NC LICFN5r NO. F-0374 Proj. No: 201 20084.00.M

SEASONAL HIGH WATER TABLE DETERMINATION
Onslow County Government Center
Onslow County, North Carolina
Catena Job # 7508
Prepared For:
Daniel K. Schaefer, P.E.
Froehling & Robertson, Inc.
310 Hubert Street
Raleigh, NC 27603
Prepared By:
The;
1WRIN11h. Catena
� . v Graup
s Z06
410-B Millstone Drive
Hillsborough, NC 27278
Tel [phone] Fax [phone]
August 20, 2012
John C. Robe
A

INTRODUCTION
Froehling & Robertson, Inc. (F&R) is investigating the construction of a stormwater best
management. practice (BMP) device within the proposed Onslow County Government Center site
located along Northwest Corridor Boulevard, Jacksonville, North Carolina. Stormwater BMPs
are being considered to collect and treat runoff From adjacent impervious surfaces. As part of the
application process, a soils investigation detailing soil type and depth to seasonal high water
table (SHWT) is required. The Catena Group, Inc (Catena) has been retained to perform the
soils investigation.
INVESTIGATION METHODOLOGY
Prior to the field investigation, the Onslow County Soil Survey was referenced to get an
overview of the possible soil series located within the project study area. Two soil series were
identified in proximity of the proposed BMP. Table l presents the two soil series mapped at the
two boring locations.
Table 1. Mao Unit Svmbol and Soil Series
Map Unit Soil Series Taxonomic Class
_�mbol
AuB Autryville loamy fine sand Loamy, siliceous, thermic Arenic Paleudults
BaB Baymeade fine sand Loamy, siliceous, thermic Arenic Hapludults
The field investigation was performed on August 10, 2012. Two soil borings were advanced via
a hand auger at predetermined locations and located with a GPS unit (Figure 1). Observations of
the landscape (slope, drainage patterns, past use, etc.) as well as soil properties (depth, texture,
structure, seasonal wetness, restrictive horizons, etc.) were recorded. Soil color was determined
with a Munsell Soil Color Chart. A field verification meeting was performed on August 20,
2012, with Mr. Vincent Lewis, a representative of the NC Department of Environmental and
Natural Resources (NCDENR).
RESULTS
Soil Type and Depth to SHWT
Table 2 presents each boring with a soil series determination and the SHWT determination as
agreed upon by Catena and Mr. Lewis. The soil series determination was made by comparing
Catena soil boring descriptions to the NRCS Official Series Description (OSD). The depth to the
SHWT was noted at each boring based on a combination of redoximorphic features, presence of
saturated soil, organic staining, and best professional judgment. Full soil profile descriptions are
attached.
Onslow County Government Center-SHWT August 20, 2012
Calena Job ##7508 1

Table 2. Deoth to Seasonal High Water Table
Soil Boring Soil Series Determination SHWT Determination
# (inches helow existing surface)
SHWT#1 Baymeade 37
SHWT#2 Baymeade 41
CONCLUSIONS
The findings presented herein represent Catena's professional opinion based on our site and soils
evaluation. Our soil evaluation revealed a SHWT depth for soil borings SHWT#1 and SHWT#2
of 37 and 41 inches, respectively. These depths were further verified by a representative of
NCDENR. This report is provided to assist in the application for stormwater BMPs by providing
the supplemental soil information only. Approval for construction of the BMP must be
authorized by the NCDENR.
Onslow County Government Center-SHWT August 20, 2012
Catena Job #7508 2

The
Catena
Group
Client:
•r
OnIsow County
Government Center
SHWT Determination
Onslow County, North Carolina
Date:
August 2012
Scale.
0 2550 100 Feet
I I t II
Job No.:
7508
Figure

The Catena Group, Inc
410-B Millstone Drive
Hillsborough, NC 27278
919.732.1300
SOIL EVALUATION FORM
Property
Date of Evaluation: 8'/0-0o14
County: On.S ln� i
Sheet: i of
b
structure /
Texture
Consistence/
Mineralogy
Matrix
Color
Mottle Colors
(Quantity, Size, Contrast, Color)
is
V
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7. ..Y
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1
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4
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Evaluated by: :;'-c Z _„