SW7080503_HISTORICAL FILE_20210629

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO. SW
DOC TYPE ❑ CURRENT PERMIT
❑ APPROVED PLANS
HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE(
YYYYMMDD

ROY COOPER
Governor
JOHN NICHOLSON
Interim Secretary
BRIAN WRENN
Director .
WaAa
NORTH CAROLINA
Environmental Quality
June 29, 2021
Pasquotank County
Attention: Sparty Hammett, County Manager
206 E. Main Street
Elizabeth City, NC 27909
Dear Mr. Hammett:
Subject: Stormwater Permit Renewal
Stormwater Management Permit SV 7080503
Pasquotank County RO Water Treatment Plant, Ph II
Pasquotank County
A Division of Energy, Mineral, and Land Resources file review has determined that
Stormwater Permit SV 7080503 for a stormwater treatment system consisting of a wet
detention pond serving the RO Water Treatment Plant Ph, II located on Foreman Bundy
Road, Elizabeth City, NC expires on December 30, 2021. This is a reminder that permit
renewal applications are due 180 days prior to expiration. We do not have a record of
receiving a renewal application.
Please submit a completed permit renewal application along with a $505.00 fee for
permit renewal. Also, it was noted in the file review that a designer's certification that the
project was constructed in accordance with the approved plans as required by the
permit has not been submitted. Please include this with your application. Permit
application forms for renewal can be found on our website at:
https://deq.nc.gov/about/divisions/energy-mineral-and-land-
resources/stormwater/stormwater-program/post-construction-2. North Carolina General
Statutes and the Coastal Stormwater rules require that this property be covered under a
stormwater permit.
If you have questions, please feel free to contact me at [phone]. 1 will be glad to
discuss this by phone or meet with you. If you would like, I can e-mail you a copy of the
application forms. You can request a copy by e-mailing me at
roaer.thoroe a0ncdenr.aov.
Sincerely,
Roger K. Thorpe
Environmental Engineer
—Ej' North Carolina Department of Environmental Quality I Division of Energy. Mineral and Land Resources
�Washington Regional Office 1943 Washington Square ;Mall i Washington.North Carolina 21889
252.946.6431

r '1
AMMA-a
MCDENR
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Beverly Eaves Perdue Coleen H. Sullins Dee Freeman
Governor Director Secretary
February 16, 2009
Mr. Randy Keaton, Manager
Pasquotank County
P.O. Box 39
Elizabeth City NC 27909
Subject: Stormwater Review SW7090207
Pasquotank RO Effluent Force Main Project
Pasquotank County
Dear Mr. Keaton:
The Washington Regional Office received a copy of your Sedimentation and Erosion
Control application for the proposed RO Water Plant effluent force main project located in
Pasquotank County on February 5, 2009. Staff has determined that the project, as proposed,
consists of activities that will not pose new surface water quality threats from stormwater
runoff since no significant new impervious area is proposed. The Director has determined
that projects that are reviewed and approved by the Division as not posing water quality
threats from stormwater runoff should not be subject to the stormwater management
permitting requirements of 15A NCAC 2H.1000. For this reason, we are informing you by
way of this letter that your project will not require a stormwater management permit.
Please keep in mind that this determination does not affect your legal requirements to obtain
other permits which may be required by the Division of Water Quality, the Division of Land
Resources, Division of Coastal Management or any other Federal, State or Local
Government.. In addition, any future modifications to the project will require additional
review from this office to assure that stormwater impacts are not an issue.
North Carolina Division of Water Quality Internet: wu,w.nctvateroualitv.ore
943 Washington Square Mall Phone: [phone]
Washington, NC 27889 FAX [phone]
An Equal Opportunity/Affirmative Action Employer— 50%Recycled110% Post Consumer Paper
NorthCarolina
Naturally

Page 2
February 16,2009
If you have any questions or need additional information concerning this matter, .please
contact me or Roger Thorpe at [phone].
k4incerely,
Al Hodge—; Regional Supervisor
Surface Water Protection Section
Washington Regional Office
cc: Doug Huggett, DCM
Washington Regional Office
Central Files

142a-Il-09/ bjelo
FINANCIAL RESPONSIBILITY/OWNERSHIP FORM
SEDIMENTATION POLLUTION CONTROL ACT FEB — 5 2009
No person may initiate any land -disturbing activity on one or more acres as covered by the Act before t fish `ri-t+t�fa.
form and an acceptable erosion and sedimentation control plan have been completed and approved by the
Land Quality Section, N.C. Department of Environment and Natural Resources. (Please type or print and, if
the question is not applicable or the e-mail and/or fax information unavailable, place N/A in the blank.)
Part A.
1. Project Name Pasquotank County Reverse Osmosis Water Treatment Plant - 12" Effluent Force Main
2. Location of land -disturbing activity: County . Pasquotank City or Township Elizabeth City
Highway/Street: See Attached 7 Latitude 36016'95"N Longitude 76021'64"
r
3. Approximate date land -disturbing activity will commence: June 09
4. Purpose of development (residential, commercial, industrial, institutional, etc.): Utility
5. Total acreage disturbed or uncovered (including off -site borrow and waste areas): 15
6. Amount of fee enclosed: $975.00 . The application fee of $65.00 per acre (rounded
up to the next acre) is assessed without a ceiling amount (Example: a 9-acre application fee is $585).
7. Has an erosion and sediment control plan been filed? Yes No Enclosed
8. Person to contact should erosion and sediment control issues arise during land -disturbing activity:
Name Ed Lawler
Telephone [phone] Cell #
E-mail Address elawlerld)hobbsuochurch.00m
9. Landowner(s) of Record (attach accompanied page to list additional owners):
Part B
Fax # [phone]
FEB 0,5 2nnq
LAND QUALITY SECTION
1. Person(s) or firm(s) who are financially responsible for the land -disturbing activity (Fft8 QTON REGIONAL OFFI^E
comprehensive list of all responsible parties on an attached sheet):
Pasquotank County
Name
P.O. Box 39
Current Mailing Address
Elizabeth City NC 27907
City State Zip
252-335-0865
Telephone
206 East Main Street
Current Street Address
252-335-0866
Fax Number
Elizabeth City NC 27909
City State Zip

T�®��Lqa
2. (a) If the Financially Responsible Party is not a resident of orth Carolina, give name and street address
I/ t :]'I
of the designated North Carolina Agent:
s -:,NIA RE.0 IV
NIA
Name E-mail Address
Current Mailing Address
City State Zip
Telephone
FEB 0;5 7004
Cunent Street Address LAND QUALITY SECTION
WASHINGTON REGIONAL OFFICE
City State Zip
Fax Number
(b) If the Financially Responsible Party is a Partnership or other person engaging in business under an
assumed name, attach a copy of theCertificateof Assumed Name. If the Financially Responsible
Party is a Corporation, give name and street address of the Registered Agent:
Randy Keaton
Name of Registered Agent
P.O. Box39
Current Mailing Address
Elizabeth City NC 27907
City State Zip
Telephone [phone]
keatonr(a).co.Dasauotank.nc.us.
E-mail Address
206 East Main Street
Current Street Address
Elizabeth City NC 27909
City State Zip
Fax Number 252-335.0866
The above information is true and correct to the best of my knowledge and belief and was provided
by me under oath (This form must be signed by the Financially Responsible Person if an individual
or his attomey-in-fact, or if not an individual, by an officer, director, partner, or registered agent with
the authority to execute instruments for the Financially Responsible Person). I agree to provide
corrected information should there by any change in the information provided herein.
Randy Keaton County Manager
Type or Print Name 9 Tile or Authority
Signature ! - - Date
I, a naki S. 3Cn n in Q S , a Notary1 Public of the
/County of etet_ Sgt-rt 1 TLLN 1
State of North Carolina, hereby certify that K.�.nd../ K �a,eh U appeared
personally before me this day and being duly swom acknowledged at the above form was
executed by him.
Witness my hand and notarial seal, this ,2a rd day of TcL20 /7 r
t, •.., :. tf,�,�+�'. _. �C,�27iAJ E� `�12N/l.lr/�-Pi0
°,-Seal Notary Kctl eh S, �r nrny
My commision Expires ,S '� p
i

Hobbs, Upchurch & Associates, P.A. By: JefPThompson
rJ4Consulling Engineers Date: (� l ci y
14878 U8 Hwy 17, Hampstead, NC 28443 Page:
PROJECT: Po s qa , a O tP' `o _ { S W i"\
DESCRIPTION: A ±1 C

Stormwater Management Permit Narrative
Pasquotank County Reverse Osmosis Water Treatment Plant
Pasquotank County, NC ReEUE ,�V
May 2008 MAY - 5 2008
Project Description Di Lf Q-WARD
Pasquotank County currently owns and operates a 2.7 MGD water filtration plant located in
Weeksville. This plant serves the Pasquotank County water system (approximately 5,500
connections spread throughout the County) and currently operates at an average daily flow of 1.4
MGD, as per the Preliminary Engineering Report (PER) prepared by Hobbs, Upchurch &
Associates P.A., dated September 2007. The water treatment plant was constructed in 1981,
expanded in 1987, and utilizes groundwater from a series of wells in the Yorktown aquifer.
The proposed project, the Pasquotank County Reverse Osmosis Water Treatment Plant, will
supplement the water production from the existing Weeksville plant. The proposed reverse
osmosis plant is being designed to produce 5.0 NIGD but initially will be able to produce only
2.0 NIGD. This treatment facility will be constructed in the western portion of the County. Raw
water will be supplied through several deep aquifer production wells. The finished water will be
distributed through a 24-inch potable water main. Finished water also will be sold to Perquimans
County and Elizabeth City. The reverse osmosis (RO) concentrate ultimately will be discharged
to the Albemarle Sound through a 12-inch discharge main.
Phase I -of the initial-2-0-MGD RO WTP will feature the-drilling-of_Tour_(4)=deep wells:into the
Castle Hayne aquifer, a 24-inch raw water main, the rough earthwork for the plant site, and a
portion of -the 12-i-inch reverse osmosis concentrate discharge main (at Halls Creek near the
confluence with Little River). These items are being permitted and constructed prior to the rest
of the facility as a result of an agreement with NC DWQ over the discharge of development and
testing water from the four (4) proposed wells.
Phase 11, will construct the proposed water treatment plant which will utilize reverse osmosis
membrane technology to remove all pertinent contaminants from the raw water.
An Environmental Assessment for the proposed project was prepared by Hobbs, Upchurch &
Associates, P.A. and finalized in June 2006. A Finding of No Significant Impact (FONSI) for
the proposed project was issued on June 30, 2006. The NPDES Permit Number NCO088480 for
the permanent discharge location in the Albemarle Sound was issued on September 26, 2007 to
become effective November 1, 2007.
Site Description
The proposed project site is located in the western portion of Pasquotank County, approximately
6.5 miles west of Elizabeth City. The RO WTP will be located 1,000 feet west of the Foreman
Bundy Road (SR 1144) and Okisko Road intersection. Nearly the entire project area has been
heavily influenced by human impacts.
Per the pending future land use plan, the WTP, water main, and discharge areas will be
designated as "Rural Agricultural'. All aspects of this project will be consistent with the
designated land use classification, as stated in the EA.

2
Adiacent Property
The unincorporated area of Pasquotank County is primarily cropland and forest, as stated in the
EA. All forested land has been disturbed in the past and loss of forest habitat is expected to
continue. Additionally, the natural flow regime and hydrology patterns have been altered and
natural habitats have been severely fragmented. Residential land uses are confined to individual
homes along primary and secondary roads and urban areas.
All work will be completed within the limits of the existing property as well as the stormwater
permit, when received.
Soils
As stated in the EA, all soils in Pasquotank County are classified as hydric soils. These soils
have limitations for urban uses due to wetness, low strength, and restricted permeability. It is
estimated that approximately 3% of the total Pasquotank land area contains soils that are
identified as prime farm soils. The largest concentrations of those classified soils are located in
the southern peninsula area, southeast of the Elizabeth City urban area.
Principal soil types occurring in the proposed WTP site are from the Roanoke series consisting
of poorly drained soils derived from marine and fluvial sediments. Slopes range from 0 to 2%.
Soils identified in the vicinity of the proposed WTP include Elkton (silt loam) and Bertie (fine
sandy loam). Principal soil types found in the vicinity of the proposed discharge site are
Chapanoke (prime farmland) and Elkton, which are silt loam in composition.
Stormwater Management
This Stormwater Management Permit Narrative has been prepared as part of the required
information supplied in the stormwater permit application process.
For Phase I of the proposed project (to include site preparations for the lands for the entire,
finished RO WTP project), approximately 1 I.1 acres of 100% pervious, previously disturbed
land will be disturbed again. Impervious areas upon the completion, Phase II, of the total RO
WTP project will be 107,979 square feet (to include building, tanks, pavement, pads and
walkways). Pervious areas will be 413,776 square feet.
Once the Stormwater Management Plan is approved and other applicable permits are received;
then, Pasquotank County will begin construction with the placement of all temporary erosion and
sedimentation control devices, and utilizing best management practices, as specified in the
project design. Soil excavated from the on -site borrow pit will be used to build up the adjacent,
proposed RO WTP site. Then, the borrow pit will be used temporarily to hold waters from the
testing of the test well site on Foreman Bundy Road. After site grading, a layer of topsoil from
the borrow pit will be used to cover the proposed RO WTP site to facilitate the establishment of
vegetation resulting from seeding and mulching, as part of the erosion and sedimentation control
planning measures. Also, a temporary sediment basins will be excavated to handle any runoff
during the settling period for the adjacent RO WTP site. Inspection of the site will be requested
as soon as construction areas have been stabilized.

3
Temporary erosion control measures will be left in place until the completion of Phase II at the
WTP site. Once the site is stabilized, erosion control measures will be removed. The permanent
stormwater detention pond then will be constructed and placed into use.
Calculations
The spreadsheets containing the calculations for the sediment basins, swales, and stormwater
pond already have been distributed. These calculations were based upon the entire existing
project area being considered impervious (prior to construction) and the existing drainage
patterns being utilized. The sizing of the swales for the proposed RO WTP site were done to the
25-year design event. Pond routing calculations already were provided with the erosion control
permit.

Hobbs, Upchurch & Associates, P.A.
VJ4 Consulting Engineers
300 S.W. Broad Street • Southern Pines, NC 28387
May 27, 2008
Mr. Ernest Odei-Larbi _
Environmental Engineer
I".EEG Z. a 9
Z.Fi n
N.C. Department of Environment and Natural Resources, Washington Regional Office
943 Washington Square Mall M�� 2 Z00B
Washington, NC 27889
Re: Pasquotank County Reverse Osmosis Water Treatment Plant DWQ-tlffARO
I-IUA No: PA0603
Stonnwater Review: SW7080503
Dear Mr. Odei-Larbi:
To ensure accountability for requested information ( letter dated May 13, 2008) each comment has been
individually answered below:
I . Your narrative clearly state that no impervious surface is proposed in Phase 1, however the stormwater
management permit application has proposed impervious area of 85,560 square feet in Phase 1 and Phase 11
according to the narrative has an impervious area of 107,979 square feet. Please address this inconsistency.
• Due to design changes the impervious area of the project has varied. It was an error for the
inconsistent numbers to be reported in the submittal.
2. Please stormwater management permit application had the Project name as Reverse Osmosis Water
Treatment Plant-Phasel but the plans submitted is showing Reverse Osmosis Water Treatment Plans —Phase
II on the title block of Sheet WTP-2, 3&7. Please the project name listed on permit application should
correspond to the project name listed on the title block of plan. If you intend to secure pennit for Phase I&ll
then the project name on the permit application should listed as Reverse Osmosis Water Treatment Plans -
Phase I&It and the impervious area in Phase 1 & 11 should be listed in the permit application
• The requested Stormwater Permit is for Phase If only. A stormwater permit for Phase I was
applied for but not required since no impervious area will be created.
Please clearly delineate drainage area for Phase I and Phse 2 on exiting site plan or clearly note on plan what
Phase 1 & 11 entails. Please submit only two copies of plans in case of any changes on plans.
• Sheets WTP-2 and W 1'P-7 have been updated to reflect what Phase 11 entails.
It appears wet detention pond has been designed to treat runoff from 107,797 square feet of impervious area
from Phase 11 and not from Phase I since Phase I has no impervious area. Please check wet detention
supplement form to ensure that impervious area listed corresponds to the Phase II impervious area; wet
detention pond will have to be redesign with the correct impervious area.
• The stornnvater detention pond was initially designed to treat 85,560 SF (47.5%) of impervious
area. However, recent design changes have reduced the impervious area to 80,000 SF (400%). 'rhe
application has been updated to reflect this amount. The pond design will not change since the
permitted amount is less than the design amount.
Southern Pines, NC • Telephone [phone] • Fax [phone] • email: [e-mail]
Myrtle Beach • Raleigh • Charlotte • Kill Devil Hills

Stormwater Review SW7080503
Page 2/2
5. Please check the scale listed for the plan view of wet detention pond on Sheet WTP-8; it is 1:30 scale not
1:50.
• Correct, the scale is 1:30. 'rhe scale drawn on the plans is true to scale.
On behalf of Pasquotank County, we appreciate your assistance with this important project. If you have
any questions or need any additional information, please feel free to call.
Sincerely,
HOBB, UPCHURCH & ASSOCIATES, P.A.
es D. Freeman, E.I.
Project Engineer
Southern Pines, NC . Telephone [phone] . Fax [phone] . email: [e-mail]
Myrtle Beach . Raleigh . Charlotte . Kill Devil Hills

Pasquotank WTP SWM - Pond Routing Report 10/11/2007
P -
0
o
to
f
d
�
Q
Pond Routing Report
Normal Pool Ele (ft):
6.00
Storm Routed;
1-vr
10-pr .-
- 100-vr
\\SSE (feet):
6.91
7.62
8.50
Max. Outflow from Pond(all outlets):
0
7
9
OUTLET DATA:
Max. Flow
Dlax. flow
Max. Flow
(cfs)
(cfs)
(cfs)
Rectangular
Riser
Riser
Rim Ele (ft):
1000.00
0
0
0
Open (ft): _
4.0 x 4.0
Barrel
Inv. Ele (ft):
1000-00
Dia (in):
15.00
Circular
Riser
Riser
Run Ele (ft):
7.00
0
7
9
Dia (m):
24
Barrel
Inv. Ele (ft):
550
Dia (in):
15
3-Stage
Weir
Aluminum (1)
Ele (ft)
1000.00
0
0
0
Length (ft)
8
Conc. 2 O
Ele (ft)
1000.00
(ft)
36
Earth (3)
Ele (ft)
I000.00
Length (ft)
0
Separate
Weirparate
Se
Ele (ft)
1000.00
0
0
0
Length ft
12
Note: While this theoretical pond routing includes the 100 year event, the hydraulic calculations do not
consider the backwater effects during the 100-year event. This pond is located in the 100-year
floodplain, hence the pond will not function during such extreme events.
Prepared by jthompson Page 1 of 12

Pasquotank WTP SWM - Pond Routing
Drainage Area (so: 180,134
Drainage Area (ac): 4.14
Impetuous Area (so: 85,5607'
Impervious W 47.5%
W,IP Design Rainfall:
1 —5-1 in
_ Runoff Volu_m_e Esrimate (SCS Curve Number Method)
CN —1 85 ISCS Curve Number
C=1 0.7 Rat'I Coeff. (0.02'1CN-1)
S = 1000 _10 S =
1.76
CN
R.O. (in) _ (P - 0.2'S)^2
(P + 0.8=5)
_ _ - ---10-yr
1 r
100-yr
R.O. (in) = 1.00
R.O. (in) = 2.73
R.O. (in) = 4.68
R.O. (, = 14,984
R.O. (cf) = 40,944
JR.O. (cf) = 70,267
BMP Design Rmnfall: 15
in
R.O. (in) = 0.45 R.O. (co =
6,783
Runoff Volume Estimate (Simple Method)-
_ - _ _
Rv = 0.05 -' 0.9 + In la = Imperious Friction
_ Rv= 052 Rv = Runoff Coefficient
_
V=3630 ' Rd " Rv't A V = Volume of Runoff (co
Rd = Rainfall Depth (in)
A = Drainage Area (ac)
___... -
1 �r
10-vr
100-vr'
R.O. (in) = 1.18
R.O. (in) = 2.24
JR.O. (in) = 3.33
R.O. (c t) _ ]7,718
R.O. (co = 33,564
JR.O. (cO = 49,955
Bf\II' Design Rainfall: 1.5 in
K.O. (in) = 0.78 R.O. (cf) = 11,708
Time of Concentration and Intensity Derivations:
Kirpicli s Equation: Tc = - K' (L^__3/H)^0.385
128
L = 400 �Hydrau[ic Length of watershed (h)
H = 45 !Elevation cliff. along "L" (ft)
K = I 1%lultiplier for flow path conditions
(see FIRM supp. p2-4)
Tc = 5.00 nun.
✓ coeff I = 9 (from H&\I p. 2-6)
listed in FIRM h + T
supplement p. 5-3 T = Tc
1- r
10-yr
100-yr '
P (in) = 2.27
P (in) =1 4.3
P (m) = G.4
g=! 111
g=i 213
g= 318
h — 19
It
h = 28
I.(in/hr) = 4.63
—25
1 (in/h,) = 7.10
I (in/hr) __ 9.64
Peak Flow (Rational Method)
- _ _ Q (cfs) = CL'1
Q (cfs) = 13 Q (cfs) = 21 Q (cfs) = 28
Tp (nun) 13.4 1 T (min) 23.9 T. (min) 30.2
10/11/2007
Prepared by jthompson Page 2 of 12

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Pasquotank KIP SWM - Pond Routing Routing Plot (1) 10/1112007
16
14
12
10
W
8
a
6
4
2
20
40
60 80
Time (inin)
-0 Direct Inflow
—a— Outflow
A Other Inflow
-6 Total Inflow
100
120
140
Prepared by jthompson Page 7 of 12

Pasquotank WTP SWM - Pond Routing Routing Plot (10) 10/11/2007
25
20
15
10
0 50 100 150 200 250 300
Time (min)
Prepared by jthompson Page 8 of 12

Pasquotank WTP SWM - Pond Routing Routing Plot (100) 10/11/2007
30
25
20
10
5
0
100-yc
—0— Direct Inflow
Outflow
Other Inflow
—� Total Inflow
LL
r,
50 100 I50 200 250
Tune (inin)
300 350 400
Prepared by jthompson Page 9 of 12

Pasquotank WTP SWM - Pond Routing WQ Riser 10/11/2007
Water Quality (WQ) Riser:
1) Determine temp. pool level and volume.
2) Set elevation of Temp. Pool.
3) Interpolate the average surface area of the temp. pool volume.
Temporan, Pool Volume: 18,087 c.f
Desired Drawdown time: 1 3.3 days
Number
of Holes:
1
Diameter of I-Iolcs:j
2 in
Area of hole:
Orifice Coeff.:I
3.14 in^2
0.60
=
0.02
ft^2
WQ Pool Depth:i 1 ft
WQ
Pool Area:
15463
Pool)
(Consider the side slopes and use the average area between WQ Pool and Norm.
Desired Drawdown time (min):
4752
1 Outflow value at Tdesired (cfs): 10.000
Drawdown Curve Data
Height over
Change in
Change in
Time
Time
C/L of hole:
Outflow
Volume
Height
New Height
(days)
(min)
(ft)
(cIs)
(co
(ft)
(ft)
0.00
0
1
0.105
95
0.006
0.994
0.01
15
0.994
0.105
94
0.006
0.988
0.02
30
0.988
0.104
94
0.066
0.982
0.03
45
0.982
0.104
94
0.006
0.976
0.04
60
0.976
0.104
93
0.006
0.970
0.05
75
0.970
0.103
93
0.006
0.964
0.06
90
0.964
0.103
93
0.006
0.958
0.07
105
0.958
0.103
93
0.006
0.952
0.08
120
0.952
0.102
92
0.006
0.946
0.09
135
0.946
0.102
92
0.006
0.940
0.10
150
0.940
0.102
92
0.006
0.934
0.11
165
0.934
0.102
91
0.006
0.928
0.13
180
0.928
0.101
91
0.006
0.922
0.14
195
0.922
0.101
91
0.006
0.916
0.15
210
0.916
0.101
90
0.006
0.910
0.16
225
0.910
0.100
90
0.006
0.904
0.17
240
0.904
0.100
90
0.006
0.899
0.18
255
0.899
0.100
90
0.006
0.893
0.19
270
0.893
0.099
89
0.006
0.887
0.20
285
0.887
0.099
89
0.006
0.881
0.21
300
0.881
0.099
89
0.006
0.876
0.22
315
0.876
0.098
88
0.006
0.870
0.23
330
0.870
0.098
88
0.006
0.864
Prepared by jthompson Page 10 of 12

Pasquotank WTP SWM - Pond Routing WQ Drawdown Curve 10/11/2007
L zuu
1.00
0.80
w
v 0.60
ro
W
Q
°b9 0.40
v
x
0.20
0.00
-0.200
Water Quality Drawdown Curve
0
0
0
o
0. 0 1.00 2.00 3.00 4.00 3.00 6.)0
Time (days)
Prepared by jthompson Page 11 of 12

Pasquotank WTP SWM - Pond Routing Drain 10/11/2007
Drain Valve Sizing:
1) Determine the lowest possible elevation for a drain valve.
2) Determine the average pool area between riser top and drain invert.
3) Determine the Volume and Height of water above the drain valve.
Drain Volume: cf
Desired Drawdown time: 1.0 days
Number of Holes:
1
Diameter
of I -toles:
4 in
Area of hole:
Orifice Coeff:
12.57 in^2 =
0.60
0.09
ft^2
Max. Pool Depth: 1.5 ft
Avg.
Pool Area:
1 __ 16500
pool)
(Consider the side slopes and use the average area between WQ Pool and Norm.
Desired Drawdown time (min): 1440
1 Outflow value at Tdesired (cfs): 10.010
Drawdown Curve Data
Height over
Change in
Change in
Time
Time
C/L of hole: Outflow
Volume
Height
New Height
(days)
(min)
(ft) (cfs)
(co
(ft)
(ft)
0.00
0
1.5 0.515
463
0.028
1.472
0.01
15
1.472 0.510
459
0.028
1.444
0.02
30
1.444 0.505
454
0.028
1.417
0.03
45
1.417 0.500
450
0.027
1.389
0.04
60
1.389 0.495
446
0.027
1.362
0.05
75
1.362 0.490
441
0.027
1.336
0.06
90
1.336 0.486
437
0.026
1.309
0.07
105
1.309 0.481
433
0.026
1.283
0.08
120
1.283 0.476
428
0.026
1257
0.09
135
1.257 0.471
424
0.026
1.231
0.10
150
1.231 0.466
420
0.025
1.206
0.11
165
1.206 0.461
415
0.025
1.181
0.13
180
1.181 0.457
411
0.025
1.156
0.14
195
1.156 0.452
407
0.025
1.131
0.15
210
1.131 0.447
402
0.024
1.107
0.16
225
1.107 0.442
398
0.024
1.083
0.17
240
1.083 0.437
393
0.024
1.059
0.18
255
1.059 0.432
389
0.024
1.035
0.19
270
1.035 0.428
385
0.023
1.012
0.20
285
1.012 0.423
380
0.023
0.989
0.21
300
0.989 0.418
376
0.023
0.966
0.22
315
0.966 0.413
372
0.023
0.943
0.23
330
0.943 0.408
367
0.022
0.921
Prepared byjthompson Page 12 of 12

PASQUOTANK REVERSE OSMOSIS WATER TREATMENT PLANT
Hrdrograph formulation
Drainage Subarea: SD -I Phase 11
Time of Concentration and Intensity Derivations:
1 xs
Kirpich's Equation:
"I'c = 1 8 J H
_ L= 50
Hydraulic Length of watershed (ft)
Acres _ _ C Wen94
H = 0.5
Elevation diff. along "L" (ft)
Impervious Area (ac) _� 1.1 0.85
K= 1.0
Previous Area (ac) = 0.67 0.25
(IiRM supp.p2-4)
1.77
Tc=
5.0 min.
g d h are regression
coeff I — g
listed in IIRM h+T Total C= Impervious Weighted + Pervious Weighted
supplement p.5-3 T=Tc Total Area
213 (HRM supp. p24)
h = 25 ITotal C = 0.62
(in/fir) = 7.10
Peak Flow (Rational Method)
nrrrcl=CiA
Design Q (cfs): 7.83 Start Sta. (ft): 0+00 End Sta. (ft): 3+93
Start FL (ele): 7.40 End FL (ele): 6.50
Channel Flow (Manning's Equation):
Manning's n =
Long. Slope S =
Side Slopes Z =
Depth d =
Base B =
0.030
0.0023
3
1.25
0
r//t
: !
ft
ft
Area A =
4.69
FT'
Wetted. Perim. P =
7.91
FT
Ilvd. Radius R =
0.59
Max. Flow Rate Q =
7.88
CFS
Velocity (Qa max flow) V=
1.68
FPS
Top Width W =
7.50
FT
Q = 1.49 AR,7,4
.,
Swale calcs PA0603 REV 3-25-08 JD Freeman 1/1

PASQUOTANK REVERSE OSMOSIS
WATER TREATMENT PLAN
Hvdrograph jbmndation
Drainage Subarea: SD-2
Phase II
Time of Concentration and Intensity Derivations:
K 1
'
385
Kirpich's Equation:
Tc=
[128 J
H
L = 250
Hydraulic Length of watershed (ft)
_Acres C Wei Filed
H = 0.5
Elevation diff. along "L" (ft)
Impervious Area (ac) =
1.56 0.85
1.33
K= 1.0
Previous Area (ac) =
2.82 0.25
0.71
(FIRM supp. p2-4)
4.38
Tc = 6.0 min.
g & h are regression
coeff I = g
listed in FIRM h+T Total C = Impervious Weighted+ Pervious Weighted
Supplement p. 5-3 T= Tc Total Area
213 (FIRM supp. p2-4)
h = 25 Total C = 0.46
I (in/hr) = 6.87
Peak Flow (Rational Method)
Q (cfs) = CiA
Q(cf,)= 13.95
Design Q (cfs): 13.95 Stan Sta. (ft): 0+00 End Sta. (ft): 7+30
Start FL (ele): 7.40 End FL (ele) 6.52
Channel Flow (Manning's F uation):
Manning s n =
Long. Slope S =
Side Slopes Z =
Depth d =
Base B =
0.030
0.0013
3
1.25
4
(t//1
:1
ft
ft
Area A =
9.69
F'rZ
Wetted Perim. P =
11.91
FT
Hyd. Radius R =
0.81
Max. Flow Rate Q =
14.53 '
CFS
Velocity (Q max flow) V=
1.50
FPS
Top Width W =
11.50
F'r
= 1.4j AK'-.
Swale talcs PA0603 REV 3-25-08 JD Freeman 1/1