SW7081206_HISTORICAL FILE_20210712

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

wuro
ROY COOPER
Governor
ELIZABETH S. BISER
serretary
BRIAN WRENN
Director
NORTH CAROLINA
Environmental Quality
July 12, 2021
Albemarle Electric Membership Corporation
Attention: Gary Ray, General Manager
125 Cooperative Way
Hertford, NC 27944
Subject: Stormwater Permit Renewal
Stormwater Management Permit SV 7081206
South Mills Subdivision
Camden County
Dear Mr. Ray:
A Division of Energy, Mineral, and Land Resources file review has determined that
Stormwater Permit SV 7081206 for a stormwater treatment system consisting of a wet
detention basin serving the South Mills Substation located on NC Hwy 343 in South
Mills, 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/d ivisions/energy-m ineral-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
roger.thorpe a(incdenr.gov.
Sincerely,
Roger K Thorpe
✓�
Environmental Engineer
North Carolina Department of Environmental Quality 1 Division of Energy, Mineral and Land Resources
IWashington Regional Office 1 943 Washington Square Mall t Washington, North Carolina 27889
���' "•^°^^^^yin\ � 252.946,6481

'yIA &d
Energy, Mineral &
Land Resources
ENVIRONMENTAL (DUALITY
October 4, 2017
Albemarle Electric Membership Corporation
Attention: Mr. Bradley V. Furr
P.O. Box 69
Hertford, NC 27944
Dear Mr. Furr:
ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
TRACY DAVIS
Director
Subject: Stormwater Permit Inspection
Stormwater Management Permit SW7081206
South Mills Substation
Camden County
On September 28, 2017, a stormwater compliance inspection was conducted at the wet
detention pond serving the South Mills Substation located near South Mills, NC. State
Stormwater permit SW7081206 was issued on February 18, 2009 for the construction
and operation of a wet detention pond to treat stormwater runoff from impervious
surfaces on the site.
Section II 6. of permit SW7081206 requires that upon completion and prior to operation
of the permitted facility, a certification must be received from an appropriate designer for
the system installed certifying that the permitted facility has been installed in
accordance with the permit, the approved plans and specifications, and other supporting
documentation. Please submit the required certification within 60 days. Failure to
comply with a permit subjects the owner to assessment of civil penalties.
If you have questions, please feel free to contact me at [phone].
Sincerely,
Ro er K. Thorpe
Environmental Engineer
Nothing Compares._
Stale of North Carolina I Environmental Quality I Energy. Mineral and Land Resralrces
Washinntnn RenirnaalOf(iar 9M13 Wavhinnlnn Snun re Mall I Washinmmn. NC 278149

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HERTFORD. NORTH CAROLINA
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MORGANS CORNER TO SOUTH MILLS
115 kV TRANSMISSION LINE
USGS QUADRANGLE MAP
Booth&Associates Inc.
DWN. BDE�
DATE: 02/26/2013
DWG. N0.
CKD. BDM
APPD. BDM
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SCALE: 1' = 2000'
FILE: 6325_W
DATE REVISION
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USGS-1
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JOB NO. 477-6325
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ALBEMARLE ELECTRIC MMEMBERSHIP CORPORATION
HERTFORD, NORTH CAROLINA
STORMWATER MANAGEMENT PLAN
FOR
SOUTH MILLS
115 kV TO 15 x 25 kV SUBSTATION
.a- SEAL r_
033726
111100
Booth & Associates, Inc.
f 2 (0 2 Da 8 Consulting Engineers
1011 Schaub Drive
Raleigh, North Carolina 27606
©December 2008

ALBEMARLE ELECTRIC MEMBERSHIP CORPORATION
HERTFORD, NORTH CAROLINA
SOUTH MILLS
115 kV TO 15 x 25 kV SUBSTATION
STORMWATER MANAGEMENT PLAN
1.0 PURPOSE
The purpose of the Stormwater Management Plan is to establish stormwater management
requirements and controls to prevent surface water quality degradation to the extent practical
in the streams and other bodies of water located in the Pasquotank River Basin. This plan is
to protect and safeguard the general health, safety, and welfare of the local and neighboring
communities. Best Management Practices (BMPs) along with several other stormwater
management and erosion sediment control practices have been implemented in the design in
order to achieve this goal.
2.0 DEFINITIONS
Best Management Practices (BMPs) — A structural or non-structural management -based
practice used singularly or in combination to reduce non -point source input to receiving
waters in order to achieve water quality protection goals.
➢ Non-structural BMPs —Non-engineering methods to control the amount of non -point
source pollution. These may include land -use controls and vegetated buffers.
➢ Structural BMPs — Engineered structures that are designed to reduce the delivery of
pollutants from their source or to divert contaminants away from the waterbody.
Conveyance — The process of moving water from one place to another.
Curve Number — An index that represents the amount of runoff from the combined
hydrologic effect of soil, land use, agricultural land treatment class, hydrologic condition,
and antecedent soil moisture. Curve numbers have a range of 0 to 100.
Design Storm — A rainfall event of specific depth or intensity (i.e. 3.12 inches or 4.80
inches/hour) and return frequency (e.g., 1-year storm) that is used to calculate runoff volume
and peak discharge rate.
Detain — To store and slowly release storm water runoff following precipitation by means of
a surface depression or tank and an outlet structure. Detention structures are commonly used
for pollutant removal, water storage, and peak flow reduction.
06-6483-SC06/447 -I- Boodi
®December 2008 OC18tPS

Evaporation — The change by which any substance is converted from a liquid state and
carried off in vapor.
Floodplain — An area adjacent to a stream or river where water overflows its banks during
high flow events..
Ground Water — The supply of fresh water found beneath the earth's surface (usually in
aquifers) that provides base flow to streams and rivers and is often used for supplying wells
and springs. The inflow to a ground water reservoir is called ground water recharge.
Hydrograph — A graphic plot of changes in the flow of water or in the elevation of water
level plotted against time.
Hydrologic Cycle (Water Cycle) — The cycle of water movement from the atmosphere to
the earth and back to the atmosphere through various processes.
Hydrologic Soil Group (HSG) — See Soil Group definition.
Hydrology — The science dealing with the properties, distribution and circulation of water.
Impervious Surface — A surface that cannot be penetrated by water such as pavement or
rock and prevents infiltration, thus generating runoff.
Integrated Management Practices (IMP) — A LID practice or combination of practices that
are the most effective and practicable (including technology, economic, and institutional
considerations) means of controlling the pre -development site hydrology.
Low Impact Development (LID) — The integration of site ecology and environmental goals
and requirements into all phases of urban planning and design from the individual residential,
commercial, and industrial lot level to the entire watershed.
Infiltration - The passage of water through the soil surface into the soil.
Permeability — The property of a soil to transmit water under a gradient. It is measured by
the quantity of water passing through a unit cross section, in a unit time, under a hydraulic
gradient.
Receiving Waters — A river, ocean, stream, or other watercourse into which runoff from
precipitation is discharged.
Recharge — The addition of water into the ground water via the surface of the ground.
06-6483-SC06/447 -2- B90th
®December 2008 fr SO 18tPS

Retain — To capture and hold storm water runoff following precipitation by means of a
surface depression allowing the water to infiltrate into the soil, evaporate and possibly
transport thus reducing the hydrologic and pollution impacts downstream. Retention
structures are commonly used for pollutant removal, water storage, and peak flow reduction.
Riprap — A facing layer (protective cover) of stones placed to prevent erosion or the
sloughing off of a structure or embankment of a waterbody.
Runoff — Water from a precipitation event that flows across the ground surface. Runoff
carries non -point source pollutants to receiving streams.
Sediment — The layer of soil, sand and minerals at the bottom of surface water, such as
streams, lakes, and rivers that may absorb contaminants.
Sedimentation — The removal, transport, and deposition of detached soil particles by
flowing water or wind.
Siltation — The deposition of finely divided soil and rock particles upon the bottom of a
waterbody.
Site Fingerprinting — A development approach that places land disturbing activities away
from environmentally sensitive areas (wetlands, steep slopes, etc.), future open spaces, tree
save areas, future restoration areas, and temporary and permanent vegetative forest buffer
zones. Ground disturbance is confined to areas where structures, roads, and rights -of -ways
will exist after construction is completed.
Soil Group —Hydrologic Soil Groups (HSG) are used to estimate runoff from precipitation.
Soils not protected by vegetation are placed in one of four (4) groups on the basis of the
intake of water (infiltration) after the soils have been wetted and have received precipitation
from long duration storms. Group A soils have a high infiltration rate and usually include
course sand and gravel. Group B soils have a moderate infiltration rate and include soils
with moderately fine to coarse texture. Group C soils have a slow infiltration rate and
include soils that have a moderately fine to fine texture. Group D soils have a very slow
infiltration rate and include fine textured clays (Soil Conservation Service, 1986).
Soil Moisture — Water diffused in the soil. It is found in the upper part of the zone of
aeration where water is discharged by transpiration from plants or by soil evaporation.
Stormwater— Water that runs across the surface of the ground during and after precipitation
events.
Swale — An open depression or wide, shallow ditch that intermittently contains or conveys
runoff. Can be used as BMP to detain and filter runoff.
06-6483-SC06/447 -3- Booth
®December 2008 fy O 1 tCS

Time of Concentration (Tc) — The time required for runoff to travel from the hydraulically
most distant point (in time) in the watershed, to the point of interest in the watershed.
Total Suspended Solids (TSS) — Total suspended matter in water, which is commonly
expressed as a concentration in terms of milligrams per liter or parts per million.
Travel Time (Tt) — The time it takes water to travel from one location to another in a
watershed. It is a component of the time of concentration (Tc).
Treatment Train —A series of BMPs or natural features, each designated to treat runoff that
are implemented together to maximize pollutant removal effectiveness.
Water Table — The upper surface of a zone of saturation or ground water.
Watershed — The area of land that contributes surface runoff to a waterbody.
Wetlands — An area (including swamp, marsh, bog, prairie pothole, or similar area) that is
typically inundated or saturated by surface or groundwater at a frequency and duration
sufficient to support the growth and regeneration of vegetation requiring an abundant water
source.
3.0 PROJECT DESCRIPTION
3.1 The purpose of this project is to construct a 115 to 15 x 25 kV substation for
Albemarle Electric Membership Corporation to satisfy the electrical needs of the
surrounding area. The substation will consist of typical structures and equipment
associated with an electrical substation. The substation will be enclosed by a chain
link fence and the ground cover within the fence will be stone.
3.2 The total property area is 3.24 acres with an encumbrance of 0.30 acres for a
proposed forty foot (40'-0") private access easement that parallels the northern
property line. Of this area, 2.62 acres will be disturbed and once construction is
complete, 1.39 acres will be impervious. The site is located in South Mills, North
Carolina along N.C. Highway 343 approximately''A mile south of the intersection of
U.S. Highway 17 and N.C. Highway 343.
4.0 PRE -DEVELOPED SITE CONDITIONS
The proposed South Mills 115 kV to 15 x 25 kV Substation is located in Camden County and
the Pasquotank River Basin. The site is also located in the Tidewater Coastal Plains
physiographic region and consists of silt loam. The depth to water table lists average depths
of zero to six inches (0" — 6 ").
06-6483-SC06/447 -4- Booth
®December 2008 OC at2S

The landscape consists of a fallowed farm field with drainage ditches on three (3) sides of
the proposed site. The site's slope is minimal ranging from 0.5 to 1.5% in the northwest
direction.
5.0 POST DEVELOPMENT SITE CONDITIONS
The post developed site will consist of approximately 2.62 t acres of disturbed area. Two
gravel access drives will connect the South Mills 115 kV to 15 x 25 kV Substation to NC
343. The drive will be a minimum of twenty feet (20'-0") wide and consist of twelve inches
(12") of compacted crusher run. The substation surface will contain a ground cover of three
inches (3") of one and one-half inch (1 %') washed stone with a base of three inches (3") of
crusher -run. The site.will be graded with a one percent (1%) slope to force stormwater
runoff in sheet flow into a grass -lined channel. The grass -lined channel will then divert the
stormwater into a wet detention basin that will have a three foot (T-0") deep permanent pool
and release the one and one-half inch (I %z") storm over a course of two (2) to five (5) days
through a twelve inch (12") PVC pipe. The basin has been sized to handle all storms ranging
from the one and one-half inch (1 %") storm through the 100 —Year Storm. The stored water
will be released through a concrete riser -barrel and an emergency spillway weir system with
Riprap Outlet Protection. Reinforced concrete pipe culverts will be installed under the
driveways and have both inlet and outlet protection. All disturbed areas on the site will be
permanently stabilized with grass.
6.0 SOIL DESCRIPTION
The site consists of two (2) basic soil types. The majority of the soil is the Roanoke silt loam
(RoA), which has zero to two percent (0-2%) slopes and a hydrologic rating of "D." The
other soil type is the Cape Fear silt loam (CfA). It also consists of a zero to two percent
(0-2%) slope, but has a slightly better hydrologic rating of "C/D." The water table on the
proposed sites varies from zero (0") to six inches (6") below grade. For additional
information, reference the Soils Report found in Exhibit No. 8.
7.0 DESIGN APPROACH
The North Carolina Erosion and Sediment Control Planning and Design Manual along with
the Stormwater Best Management Practices Manual were referenced for design requirements,
regulations and standards for this project. To adhere to these manuals, the USDA TR-20
Method, Urban Hydrology for small watersheds, was followed by using Hydro CAD®
Version 7.10. Hydro CAD® is a Computer Aided Design program for modeling the
hydrology and hydraulics of stormwater runoff. Additional calculations were performed
using Microsoft® Excel.
06-6483-SC06/447 5- Booth
®December 2008 �`r�i�.SSOC18.tPS

8.0 APPLIED PRACTICES
During the design procedure, careful attention was placed on the site location and
minimizing the effects of disturbance on the pre -developed area. The project's impervious
area is approximately forty-three percent (43%) of the total area of the property classifying
it a High Density project. Our design incorporates a grass -lined channel diverting flow into
a wet detention basin to collect the substation's stormwater runoff. The substation site is not
contributing to SA waters and therefore is only required to control a one and one-half inch
(1 %2") rainfall event. The basin has a riser -barrel and emergency spillway weir that release
the 2, 10, and 100 — Year Storms at a controlled rate into a grass -lined channel that buffers
the stormwater before it reaches the existing ditch. The existing ditches were modeled as full
in the calculations.
An eighteen inch (18") Class V (RCP) culvert will be installed under the access drives. Both
inlet and outlet protection will be placed at each culvert.
All portions of the disturbed site will be permanently stabilized with grass. The final design
provides an electrical substation design that not only protects the equipment, but more
importantly protects the environment and general public from harm.
06-6483-SC06/447 -6- Booth
®December 2008 fy S C18tPS

Albemarle EMC Date: 11/26/2008
South Mills Substation Run By: BDM
Erosion and Sediment Control Page : 1 of 1
Wet Detention Basin Calculation
Total Property Area (TPA) = 3.24 Acres
Drainage Area (DA) : 1.96 Acres Impervious Area (IA) : 1.39 Acres
Percent Impervious, (1) = 43 %
Pond Desian Criteria:
Permanent Pool Elevation : 9.0 Ft. Design Storm (DS) : 1.5 In.
Permanent Pool Length (L) : 63 to 142 Ft. Total Suspended Solids (TSS) : .85 %
Permanent Pool Width (W) : 86 Ft. Note : If TSS = 90%, No Vegetated r er s equired
Permanent Pool Depth.(D) : 3 Ft.
Minimum Reauired Surface Area At Permanent Pool:
(Refer to Surface Area to Drainage Area Ratio Table 10-2)
Surface Area to Drainage Area Ratio : SA/DA = 3.58 %
Required Permanent Pool Surface Area (RPPSA) : SAIDA x DA = ! 3057 Sq. Ft
Actual Permanent Pool Surface Area (PPSA) ` 9104 Sq. Ft. (PPSA > RPPSA)
Actual Permanent Pool Volume (PPV) : 11976 Cu. Ft.
Minimum Required Temporary Pool Area & Volume (Simple Method by Tom Schuler)
Runoff Coefficient (Rv) : 0.05 + 0.009 x I = 0.44
r
Required Temporary Pool Volume (RTPV) : DS x Rv x DA = 4654 Cu. Ft.
Curve Number (CN) : 91
Potential Maximum Retention (S) : 1000/CN - 10 = 0.99 In.
Runoff Depth (Q') : (P - 0.2S)2/(P + 0.8S) = 0.74 In.
Minimum Depth of Temporary Pool : 0.51 Ft.
Actual Depth of Temporary Pool : 1.0 Ft.
Temporary Pool Elevation : 10.0
Actual Temporary Pool Surface Area (TPSA) : 13171 Sq. Ft.
Actual Temporary Pool Volume (TPV) : 11138 Cu. Ft.
Minimum Reauired Forebay Area & Volume:
Required Forebay Volume (RFV) : 20%.x PPV = 2395 Cu. Ft.
Acutal Forebay Length : 30.00 Ft.
Actual Forebay Surface Area (FSA) : 3000 Sq. Ft.
Actual Forebay Volume (FV) : 2408 Cu. Ft.
(TPV > RTPV)
(FV > RFV)
Orifice Sizing :
Required Flowrate for a 2 Day Drawdown (RF2) : TPV / 172800 seconds = 0.0645 Cfs
Required Flowrate for a 5 Day Drawdown (kF5) : TPV / 432000 seconds = 0.0258 Cfs
Orifice Diameter: 1.5 In. - Average Head (h) = 0.47 Ft.
Actual Flowrate (AF) : Co'A'SQRT[2'g`h] = 0.0405 Cfs (RF2 < AF < RF5)
Copyright 2008 Booth & Associates, Inc.

STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form must be filled out, printed and submitted.
)quired Items Checklist (Part III) must be printed, filled out and submitted along with all of the required inforr
Project name Albemarle EMC - South Mills Substation
Contact person Bryan D. Maness, PE
Phone number [phone]
Date 11/26/2008
Drainage area number
1,2and 3
Site Characteristics
Drainage area
1.96
ft2
Impervious area
1.39
ft2
% impervious
43
%
Design rainfall depth
1.50
in
Storage Volume: Non -SR Waters
Minimum volume required
4,654
ft3
Volume provided
11,138
ft3
Storage Volume: SR Waters
1-yr, 24-hr runoff depth
N/A
in
Pre -development 1-yr, 24-hr runoff
N/A
ft3
Post -development 1-yr, 24-hr runoff
N/A
ft3
Minimum volume required
N/A
ft3
Volume provided
N/A
ft3
Peak Flow Calculations
1-yr, 24-hr rainfall depth
2.75
in
Rational C, pre -development
0.15
(unitless)
Rational C, post -development
0.80
(unitless)
Rainfall intensity: 1-yr, 24-hrstorm
0.30
in/hr
Pre -development 1-yr, 24-hr peak flow
1.86
ft3/sec
Post -development 1-yr, 24-hr peak flow
0.00
ft3/sec
Pre/Post 1-yr, 24-hr peak flow control
-1.86
ft3/sec

Basin Elevations
Basin bottom elevation
6.00
ft
Sediment cleanout elevation
6.50
ft
Bottom of shelf elevation
8.00
ft
Permanent pool elevation
9.00
ft
SHWT elevation
9.00
ft
Top of shelf elevation
9.50
ft
Temporary pool elevation
10.00
ft
Volume and Surface Area Calculations
SA/DA ratio
3.58
(unitless)
Surface area at the bottom of shelf
3,485
ft2
Volume at the bottom of shelf
5,682
ft3
Permanent pool, surface area required
3,057
ft2
Permanent pool, surface area provided
9,104
ft2
Permanent pool volume
11,976
ft3
Average depth for SA/DA tables
3.00
ft
Surface area at the top of shelf
9,759
It
Volume at the top of shelf
16,692
ff3
Forebay volume
2408
ft'
Forebay % of permanent pool volume
20
%
Temporary pool, surface area provided
13171
ft2
Drawdown Calculations
Treatment volume drawdown time
3.86
days
Treatment volume discharge rate
0.04
ft3/s
Pre -development 1-yr, 24-hr discharge
1.86
ft3/s
Post -development 1-yr, 24-hr discharge
0.00
ft3/s
Additional Information
Diameter of orifice
1.5
in
Design TSS removal
85
%
Basin side slopes
3.00
:1
Vegetated shelf slope
6.5 to 20
:1
Vegetated shelf width
23.25
It
Length of flowpath to width ratio
2.50
:1
Length to width ratio
2.50
:1
Trash rack for overflow & orifice?
Y
(Y or N)
Freeboard provided
1.00
It
Vegetated filter provided?
Y
(Y or N)
Recorded drainage easement provided?
N
(Y or N)
Capures all runoff at ultimate build -out?
Y
(Y or N)
Drain mechanism for maintenance or
Gravity Drain Not Possible; Use A Pump
emergencies

III.?REt1UIRED ITER%CHECKLIST.
Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will
result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to
indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a
requirement has not been met, attach justification.
Pagel Plan
Initials
Sheet No.
BDM
SMt
1. Plans (V - 50' or larger) of the entire site showing:
BDn
- Design at ultimate build -out,
- Off -site drainage (if applicable),
- Delineated drainage basins (include Rational C coefficient per basin),
- Basin dimensions,
- Pretreatment system,
- High flow bypass system,
- Maintenance access,
- Proposed drainage easement and public right of way (ROVE,
- Overflow device, and
- Boundaries of drainage easement.
BDM
GR3
2. Partial plan (1" = 30' or larger) and details for the wet detention basin shouting:
8uM
Outlet structure with trash rack or similar,
Maintenance access,
Permanent pool dimensions,
Forebay and main pond with hardened emergency spillway,
Basin cross-section,
- Vegetation specification for planting shelf, and
- Filter strip.
N/A
NIA
3. Section view of the dry detention basin (1" = 20' or larger) showing:
BDM
Side slopes, 3:1 or lower,
Pretreatment and treatment areas, and
Inlet and outlet structures.
BDM
GR1
4. If the basin is used for sediment and erosion control during construction, clean out of the basin is specified
&DM
on the plans prior to use as a wet detention basin.
BDM
Calculations
5. A table of elevations, areas, incremental volumes & accumulated volumes for overall pond and for Forebay,
BDM
to verify volume provided.
BDM
GR1
6. A construction sequence that shows how the wet detention basin will be protected from sediment until the
EWA
entire drainage area is stabilized.
BDM
Book
7. The supporting calculations.
UJ4
BDM
Enclosed
8. A copy of the signed and notarized operation and maintenance (0&M) agreement.
BDM
BDM
UH
NIA
9. A copy of the deed restrictions (if required).
BDM
To Be
10. A soils report that is based upon an actual field investigation, soil borings, and infiltration tests. County
DDNt
Provided
soil maps are not an acceptable source of soils information.

Permit Number:
(to be provided by DWQ)
Drainage Area Number:
Wet Detention Basin Operation and Maintenance Agreement
I will keep a maintenance record on this BMP. This maintenance record will be kept in a
log in a known set location. Any deficient BMP elements noted in the inspection will be
corrected, repaired or replaced immediately. These deficiencies can affect the integrity
of structures, safety of the public, and the removal efficiency of the BMP.
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):
® doesF1 does not incorporate a vegetated filter at the outlet.
This system (check one):
❑ does E does not .. incorporate pretreatment other than a forebay.
Important maintenance procedures:
— Immediately after the wet detention basin is established, the plants on the
vegetated shelf and perimeter of the basin should be watered twice weekly if
needed, until the plants become established (commonly six weeks).
— No portion of the wet detention pond should be fertilized after the first initial
fertilization that is required to establish the plants on the vegetated shelf.
— Stable groundcover should be maintained in the drainage area to reduce the
sediment load to the wet detention basin.
— If the basin must be drained for an emergency or to perform maintenance, the
flushing of sediment through the emergency drain should be minimized to the
maximum extent practical.
After the wet detention pond is established, it should be inspected once a month and
within 24 hours after every storm event greater than 1.0 inches (or 1.5 inches if in a
Coastal County). Records of operation and maintenance should be kept in a known set
location and must be available upon request.
Inspection activities shall be performed as follows. Any problems that are found shall
be repaired immediately.
BMP element:
Potentialproblem:
How I will remediate the roblem:
The entire BMP
Trash/debris is present.
Remove the trash/debris.
The perimeter of the wet
detention basin
Areas of bare soil and/or
erosive gullies have formed.
Regrade the soil if necessary to
remove the gully, and then plant a
ground cover and water until it is
established. Provide lime and a
one-time fertilizer application.
Vegetation is too short or too
long.
Maintain vegetation at a height of
approximatel six inches.
Form SW401-Wet Detention Basin O&M-Rev.4 Page I of 4

Permit Number:
(to be provided by DWQ)
Drainage Area Number:
BMP element:
Potentialproblem:
How I will remediate theproblem:
The inlet device: pipe or
swale
The pipe is clogged.
Unclog the pipe. Dispose of the
sediment off -site.
The pipe is cracked or
Replace the pipe.
otherwise damaged.
Erosion is occurring in the
swale.
Regrade the swale if necessary to
smooth it over and provide erosion
control devices such as reinforced
turf matting or riprap to avoid
future problems with erosion.
The forebay
Sediment has accumulated to
Search for the source of the
a depth greater than the
original design depth for
sediment and remedy the problem if
possible. Remove the sediment and
sediment storage.
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Erosion has occurred.
Provide additional erosion
protection such as reinforced turf
matting or riprap if needed to
prevent future erosion problems.
Weeds are present.
Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the plants rather than spraying.
The vegetated shelf
Best professional practices
Prune according to best professional
show that pruning is needed
practices
to maintain optimal plant
health.
Plants are dead, diseased or
Determine the source of the
dying.
problem: soils, hydrology, disease,
etc. Remedy the problem and
replace plants. Provide a one-time
fertilizer application to establish the
ground cover if a soil test indicates
it is necessary.
Weeds are present.
Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the plants rather than spraying.
The main treatment area
Sediment has accumulated to
Search for the source of the
a depth greater than the
original design sediment
sediment and remedy the problem if
possible. Remove the sediment and
storage depth.
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Algal growth covers over
Consult a professional to remove
50% of the area.
and control the algal Eowth.
Cattails, phragmites or other
Remove the plants by wiping them
invasive plants cover 50% of
the basin surface.
with pesticide (do not spray).
Form SW401-Wet Detention Basin O&M-Rev.4 Page 2 of 4

Permit Number:
(to be provided by DWQ)
Drainage Area Number:
BMP element:
Potentialproblem:
How I will remediate theproblem:
The embankment
Shrubs have started to grow
Remove shrubs immediately.
on the embankment.
Evidence of muskrat or
Use traps to remove muskrats and
beaver activity is present.
consult a professional to remove
beavers.
A tree has started to grow on
Consult a dam safety specialist to
the embankment.
remove the tree.
An annual inspection by an
Make all needed repairs.
appropriate professional
.shows that the embankment
needs repair. if applicable)
The outlet device
Clogging has occurred.
Clean out the outlet device. Dispose
of the sediment off -site.
The outlet device is damaged
Repair or replace the outlet device.
The receiving water
Erosion or other signs of
Contact the local NC Division of
damage have occurred at the
Water Quality Regional Office, or
outlet.
the 401 Oversight Unit at 919-733-
1786.
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 9__5 feet in the main pond, the sediment
shall be removed.
When the permanent pool depth reads 9__5 feet in the forebay, the sediment
shall be removed.
Sediment Removal
Bottom
BASIN DIAGRAM
ill in the blanks)
Permanent Pool Elevation 9'
6_5' I PeM anen Pool
+ Volume Sediment Removal Elevation 6.5'
6' -ft Min.
- ----------------------------------------
Sediment Bottom Elevation 6'
Storage
FOREBAY MAIN POND
1-ft
Storage
Form SW401-Wet Detention Basin O&M-Rev.4 Page 3 of 4

Permit Number:
be provided by DWQ)
acknowledge and agree by my signature below that I am responsible for the
performance of the 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.
Project name:Albemarle Electric Membership Corporation - South Mills 115 to 15 x 25
kV Substation
BMP drainage area number: 1 (Includes DA-1, DA-2 and DA-3 from Dwg DA2 of 2
Print name: Mr. Bradley V. Furr
Title: Executive VP and General Manager
Address: P.O. Box 69, 159 Creek Drive, Hertford NC 27944
Phone: [phone]
Signature:
Date:
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.
a Notary Public for the State of
County of , do hereby certify that
personally appeared before me this
day of , and acknowledge the due execution of the
forgoing wet detention basin maintenance requirements. Witness my hand and official
seal,
SEAL
My commission
Form SW401-Wet Detention Basin O&M-Rev.4 Page 4 of 4

NCDENR Stormwater BMP Manual
1
10. Wet Detention Basin
Revised 09-28-07
3:T3iVz"
.19Deseserlphon
A` we detention brim i8 a stoimwater management'facility thatincludes a permanent pool of
water.:for reuioding`pollutan__tsand additional capacity'above°thepermarieiit'pooi4rir ,etauung.
, ,
stormwater,runoff.
Regulatory'Gredits
Feast6ility
Constderatton5 '
Ao/lutkntRemaupl:;� ,
85% Totalkuspended Solids
Med Large
Land Requirement,'
25% TotabNitrogen
Med,,
CostofConstruction
A0/ Total`Phosphorus .,
Med.:
MaintenanceBurden,.
Water Quantity
Med Lazge`
TreatableDrainage BasinSize
yes
P eak•Runoff Attenuation
Med
Possi61e Site Constraints
no
Runoff 'WiLm,e Rediiction
Med
,Community Acceptafice .
Advantages
Dis1. advantages
— Can be aesthetically pleasing and caribe
- Sgmetirnes create probleaks such as
sited in both low- and.high visibility areas.
n isance odors, algae blooms, and
- Can provide: wildlife habitat and a. focal ..
robing debns:when not properly
point for recreation
Provides good: -water quantity control ior
maintained
—. Local regulations may impose
;educing the frequency of flooding events" '
unappealing f.eatures;such as fencing
kl}at cause,bank erosign:
- around basins to'reddce safety hazards '
My a[tact e'lCcessroe�waterfowl ;which'
_
can be a tiuisance and can increase fecal
coliform4 eveL9
May coptiibute toithermal pollutioii so
may not.be apprppriate inaareas where
:. - .._.., , .... ..,_.•.. _. _:.,
..,.. sepslflv,e uatj---c species live.
Wet Detention Basin 10-1 July 2007

NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
t
10.1. General Characteristics and Purpose
In wet detention basins, a permanent pool of standing water is maintained by the riser —
the elevated outlet of the wet detention basin (see Figure 10-1). Water in the permanent
pool mixes with and dilutes the initial runoff from storm events. Wet detention basins
fill with stormwater and release most of the mixed flow over a period of a few days,
slow]), returning the basin to its normal depth.
Runoff generated during the early phases of a storm usually has the highest
concentrations of sediment and dissolved pollutants. Because a wet detention basin
dilutes and settles pollutants in the initial runoff, the concentration of pollutants in the
runoff released downstream is reduced. Following storm events, pollutants are removed
from water retained in the wet detention basin. Two mechanisms that remove pollutants
in wet detention basins include settling of suspended particulates and biological uptake,
or consumption of pollutants by plants, algae, and bacteria in the water. However, if the
basin is not adequately maintained (e.g., by periodic excavation of the captured
sediment), storm flows may re -suspend sediments and deliver them to the stream.
Figure 10-1
Permanent Pool of Water in Wet Detention Basin
Wet Detention Basin 10-3 July 2007

NCDENR Stormwater BMP Manual Chapter Revised 09-25-07
Figure 10-2b
Basic Wet Detention Basin Elements: Cross -Section
Outlet above
10.2. Meeting Regulatory Requirements
vegetated'
Side slope
North Carolina rules require that a wet detention basin must be designed by a licensed
professional. Further, the designer must subsequently.certify that he inspected the
facility during construction, that the BMP was built in accordance with the approved .
plans, and that the system complies with the requirements of the rules.
To obtain a permit to construct a wet detention basin in North Carolina, the wet
detention basin must meet all of the regulation -based Major Design Elements listed in
the beginning of this section.
To receive the pollutant removal rates listed in the front of this section, the wet detention
basin engineering design must, at a minimum, meet all of the Major Design Elements
listed in the beginning of this section. Additional regulation -based requirements, and
additional good engineering practice requirements, may be required by DWQ:
Pollutant Removal Rates
Standard pollutant rates are provided in Table 4-2 in Section 4.0. Construction of a wet
detention basin also passively lowers nutrient loading since it is counted as pervious
surface when calculating nutrient loading. Further enhancing the passive reduction of
Wet Detention Basin 10-5 July 2007

NCDRNR Stormvvater BMP Manual Chapter Revised 09-29-07
10.3.2. Siting Issues
Because large storage volumes are needed to achieve extended detention times, wet
detention basins require larger land areas than many other BMPs. Wet detention basins
may not be suitable for projects with very limited available land. Permanent retaining
walls may be used to obtain the required design volumes while reducing the footprint
that would otherwise be required for earthen construction. Retaining walls utilized to
contain the permanent pool must not reduce the required 10' width of the vegetated
shelf, and must not extend to a top elevation above the lowest point of the vegetated
shelf. Retaining walls utilized to contain the temporary pool must not reduce the
required 10' width of the vegetated shelf, and must not be in contact with the
stormwater stored up to the temporary pool elevation. Two retaining walls may be
used, as shown in Figure 10-3. Or, the design may be altered to contain only one of the
two shown.
Wet detention basins may not be constructed on intermittent streams, on perennial
streams, or in jurisdictional wetlands. Large wet detention basins that include a wetland
fringe and are abandoned in place without first being drained and regraded may be
regulated as wetlands under the provisions of Sections 401 and 404 of the Clean Water
Act.
Further, DWQ will require an engineering demonstration that the installation of a wet
detention basin adjacent to wetlands will not produce adverse affects on the wetlands
water level.
The use of stormwater wet detention basins discharging to cold -water streams capable
of supporting trout may be prohibited. Stormwater wet detention basins located in such
watersheds should be augmented with engineering measures to significantly reduce or
eliminate thermal impacts.
Figure 10-3
Alternative Wet Pond Design: Retaining Wall Option
Wet Detention Basin 10-7 July 2007

NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
Table 10-1
Surface Area to Drainage Area Ratio for Permanent Pool Sizing to Achieve 85 Percent TSS
Pollutant Removal Efficiency in the Mountain and Piedmont Regions, Adapted from Driscoll,1986
Percent
Impervious
Cover
3.0
4.0
Permanent Pool Average Depth (ft)
5.0 6.0 7.0
8.0
9.0
10%
0.59
0.49
0.43
0.35
0.31
0.29
0.26
20%
0.97
0.79
0.70
0.59
0.51
0.46
0.44
30%
1.34
1.08
0.97
0.83
0.70
0.64
0.62
40 %
1.73
1.43
1.25
1.05
0.90
0.82
0.77
50%
2.06
1.73
1.50
1.30
1.09
1.00
0.92
60%
2.40
2.03
1.71
1.51
1.29
1.18
1.10
70%
2.88
2.40
2.07
1.79
1.54
1.35
1.26
80%
3.36
2.78
2.38
2.10
1.86
1.60
1.42
90%
3.74
3.10
2.66
2.34
211
1.83
1.67
Table 10-2
Surface Area to Drainage Area Ratio for Permanent Pool Sizing to Achieve 85 Percent TSS
. Pollutant Removal
Efficiency
in the Coastal Re
'on, Adapted
from Driscoll,1986
Percent
Permanent Pool Average Depth (ft)
Impervious
Cover
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5'
10%
0.9
0.8
0.7
0.6
0.5
0
0
0
0
0
20%
1.7
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
30%
2.5
2.2
1.9
1.8
1.6
1.5
1.3
1.2
1.0
0.9
40%
3.4
3.0
26
2.4
2.1
1.9
1.6
1.4
1.1
1.0
.50%
4.2
3.7
3.3
3.0
2.7
2.4
2.1
1.8
1.5
1.3
60%
5.0
4.5
3.8
3.5
3.2
2.9
2.6
2.3
2.0
1.6
70%
6.0
5.2
4.5
4.1
3.7
3.3-
2.9
2.5
2.1
1.8
80%
6.8
6.0
5.2
4.7
4.2
3.7
3.2
2.7
2.2
2.0
90%
7.5
6.5
5.8
5.3
4.8
4.3
3.8
3.3
2.8
1.3
100%
8.2
7.4
6.8
6.2
5.6
5.0
4.4
3.8
3.2
2.6
Table 10-3
Surface Area to Drainage Area Ratio for Permanent Pool Sizing to Achieve 90 Percent TSS
Pollutant Removal F.fficienry in tha Mnantain and Piedmont Raoinnc_ AdnntPd frnm Drkor ll 19Rr
Percent
Impervious
Cover
3.0
3.5
4.0
Permanent Pool Average Depth (ft)
4.5 5.0 5.5- 6.0 6.5 7.0
7.5
8.0
8.5
9.0
10%
0.9
0.8
0.8
0.7
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
20%
1.5
1.3
1.1
1.0
1.0
0.9
0.9
0.9
0.8
0.8
0.8
0.7
0.7
30%
1.9
1.8
1.7
1.5
1.4
1.4
1.3
1.1
1.0
1.0
1.0
0.9
0.9
40%
2.5
2.3
2.0
1.9
1.8
1.7
1.6
1.6
1.5
1.4
1.3
1.2
1.1
50%
3.0
2.8
2.5
2.3
2.0
1.9
1.9
1.8
1.7
1.6
1.6
1.5
1.5
60%
3.5
3.2
2.8
2.7
2.5
2.4
2.2
2.1
1.9
1.9
1.8
1.8
1.7
70%
4.0
3.7
3.3
3.1
2.8
2.7
2.5
2.4
2.2
2.1
2.0
2.0
1.9
80%
4.5
4.1
3.8
3.5
3.3
3.0
2.8
2.7
2.6
2.4
2.3
2.1
2.0
90%
5.0
4.5
4.0
3.8
3.5
3.3
3.0
2.9
2.8
2.7
2.6
2.5
2.4
Wet Detention Basin 10-9 July 2007

y NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
l
10.3.5. Temporary Storage Volume
In addition to the permanent pool volume, the basin must also have temporary pool
storage to provide volume control during storm events. This temporary pool storage
volume is located above the permanent pool, and below the 1-foot minimum freeboard
requirement. The required temporary pool volume must be calculated as specified in
Section 3.3.1.
10.3.6. Sediment Accumulation
North Carolina rules require that the wet detention basin shall be sized with an
additional volume to account for sediment deposition between clean -out intervals
(typically 5 to 15 years). DWQ requires that engineering designs for wet detention
basins include at least one additional foot of depth for sediment storage in addition to
the permanent pool volume. It is important that operation and maintenance agreements
specify that the forebay and the wet pond be cleaned out as soon as the extra sediment
storage depth is exhausted. A benchmark for sediment removal should be established
to assure timely maintenance. Calculations for volumes and sediment accumulation are
provided in Section 3.0.
10.3.7. Plant and Landscape Requirements
The design of a wet detention basin is not complete without a detailed landscaping plan.
The planting plan must be prepared by a qualified design professional licensed in North
-. Carolina (see Chapter 6 for landscape plan requirements). The landscaping plan for a
stormwater wet detention basin should provide specifications for the selection of
vegetation, its installation, and the post -installation care for the vegetated shelf, the 3:1
side slopes, the vegetative filter strip, and the immediately surrounding areas.
Wet detention basins should incorporate several diverse species of shallow water and
shallow land [wetland] vegetation on the vegetated shelf. Sections 6.2.2 and 6.2.3
discuss the planting requirements for shallow water and shallow land areas. Table 9-1
contains a list of appropriate plant species. Diversity in species increases the robustness
of the vegetated shelf by increasing the chances that some species will survive minor
changes in the permanent pool water level. This vegetation enhances pollutant removal,
protects the shoreline from erosion, and increases safety by discouraging people from
entering the basin. A wide range of potential plant species is available for this purpose.
On the tops of berms and on the exterior slopes of containment berms, maintain turf
grass in access areas; Centipede grass is recommended. Well -maintained grass stabilizes
the embankment, enhances access to the facility, and makes inspection and other
maintenance much easier. Because many plants release phosphorus in the winter when
they die off, wet detention ponds used for phosphorous control should be planted with
broad -leaf evergreen trees and shrubs.
Where trees and shrubs are part of the planting plan, they should be selected to
maximize shading, primarily along the south, east, and west sides of the basin. This has
i
Wet Detention Basin 10-11 July 2007

NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
Figure 104
Typical Submerged Orifice Outlet Configuration
iu� nrrn
Durable materials, such as reinforced concrete, are preferable to corrugated metal in
most instances. The riser should be placed in or at the face of the embankment. By
placing the riser close to the embankment, maintenance access is facilitated and flotation
forces are reduced. The design engineer must present flotation force calculations for any
outlet design subject to flotation forces. Outlets are described in greater detail in Section
5.0, Common BMP Design Elements.
Emergency overflow spillways must be designed with hardened materials at the points
where extreme conditions might compromise the integrity of the structure.
Under most circumstances North Carolina rules require a vegetative filter strip on the
discharge from a wet detention basin, along with a level spreader or other engineered
device to ensure even, non -erosive distribution of the flow. Wet detention ponds
designed for 85% TSS removal are required to discharge through a 30 foot vegetated
filter to minimize erosion and to provide additional pollutant removal. There may be
projects where it is difficult to construct a functional vegetated filter, and the outflow
must discharge to the watercourse. In these instances, additional storage should be
Wet Detention Basin 10-13 July 2007

ll NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
t� l
above. Riser openings must not permit unauthorized access. End walls above pipe
outfalls greater than 48 inches in diameter should be fenced to prevent falls.
10.4 Construction
Even moderate rainfall events during the construction of a wet detention basin can cause
extensive damage to it. Protective measures should be employed both in the
contributing drainage area, and at the wet detention basin itself. Temporary drainage or
erosion control measures should be used to reduce the potential for damage to the wet
detention basin before the site is stabilized. The control measures may include
stabilizing the surface with erosion mats, sediment traps, and diversions. Vegetative
cover and the emergency spillway also should be completed as quickly as possible
during construction.
The designer should address the potential for bedding erosion and catastrophic failure
of any buried outlet conduit. A filter diaphragm and drain system should be provided
along the barrel of the principal spillway to prevent piping. DWQ is aware of an
evolution in standard practice, and of accumulated evidence suggesting that in most
circumstances filter diaphragms are much superior to anti -seep collars in preventing
piping. DWQ strongly prefers filter diaphragms to the older design anti -seep collar.
If reinforced concrete pipe is used for the principal spillway, "O-ring' gaskets (ASTM
C361) should be used to create watertight joints and should be inspected during
- installation.
10.5. Maintenance
10.5.1 Common Maintenance Issues
Please refer to Section 7.0, General BMP Maintenance; for information on types of
maintenance, typical frequency, and specific maintenance tasks that are common to all
BMPs. The following information is maintenance that is specific to wet detention basins.
Specific items that require careful inspection for a wet detention basin include:
evaluation of the aquatic environment, vegetation, and sediment build-up.
A program of monitoring the aquatic environment of a permanent wet detention basin
should be established. Items such as water clarity and algal growth should be monitored
regularly.
The vegetation located on the vegetated shelf must be properly maintained in order to
achieve additional pollutant removal and in order to prevent bank erosion. Bare spots,
weeds, and invasive species should be noted and remedied as soon as possible to
prevent larger. problems. Although a regular grass maintenance program for the upland
locations around the BMP will reduce weed intrusion, some weeds invariably will
appear. Periodic weeding will therefore be necessary. Chemical application to control
weeds should be carefully considered and monitored. Frequent maintenance activities
such as removing debris and cutting grass will result in a facility that is both functional
and attractive.
Wet Detention Basin 10-15 July 2007

NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
i
Table 10-6
Sample Inspection and Maintenance Provisions for Wet Detention Basins
BMP element:
Potentialproblems:
How to remediate theproblem:
The entire BMP
Trash/debris is present.
Remove the trash/debris. .
The perimeter of the wet
detention basin
Areas of bare soil and/or
erosive gullies have formed.
Regrade the soil if necessary to
remove the gully, and then plant a
ground cover and water until it is
established. Provide lime and a
one-time fertilizer applicadon.
Vegetation is too short or too
Maintain vegetation at a height of
long.
ap2roximately six inches.
The inlet device: pipe or
The pipe is clogged.
Unclog the pipe. Dispose of the
swale
sediment off -site.
The pipe is cracked or
Replace the pipe.
otherwise damaged.
Erosion is occurring in the
Regrade the swale if necessary to
swale.
smooth it over and provide erosion
control devices such as reinforced
turf matting or riprap to avoid
future problems with erosion -
The forebay
Sediment has accumulated to
Search for the source of the
a depth greater than the
sediment and remedy the problem if
original design depth for
possible. Remove the sediment and
sediment storage.
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Erosion has occurred.
Provide additional erosion
protection such as reinforced turf
matting or riprap if needed to
prevent future erosion problems.
Weeds are present.
Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the lants rather than s ra in .
Wet Detention Basin 10-17 July 2007

NCDENR Stormwater BMP Manual Chapter Revised 09-28-07
Figure 10-5: Example Clean Out Diagram
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 9.5 feet in the main pond, the sediment shall
be removed.
When the permanent pool depth reads 9.5 feet in the forebay, the sediment shall be
removed.
BASIN DIAGRAM
oil in the blanks)
V Permanent Pool Elevation 9'
Sediment Removal El. 6. 5Pe manen Pool
------- ------ Volume Sediment Removal Elevation 6.5' Volume
Bottom Elevation ' ft Min .
----------- ------------ -------
Sediment Bottom Elevation 6 ,t,1-ft at
Storage - Sedimei
Storage
FOREBAY. AMAIN POND
Wet Detention Basin 10-19 July 2007

USDA United States
Department of
Agriculture
N RCS
Natural
Resources
Conservation
Service
A product of the National
Cooperative Soil Survey,
a joint effort of the United
States Department of
Agriculture and other
.Federal agencies, State
agencies including the
Agricultural Experiment
Stations, and local
participants
Custom Soil Resource
Report for
Camden County,
North Carolina
Albemarle - South Mills

Custom Soil Resource Report
Soil Map
N Meters
A 0 25 W 100 150
Feet
0 _ 100 200 400 600