SW8050547_Historical File_20121129 (2)

ME
IAi, ENR
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Beverly Eaves Perdue Charles Wakild, P. E.
Governor Director
November 29, 2012
Mr. Jon W. Rosborough, Airport Director
New Hanover County Airport Authority
1740 Airport Boulevard
Wilmington, NC 28405
Subject: Stormwater Permit No. SW8 050547 Mod.
Wilmington International Airport
High Density Dry Detention Basin Project
New Hanover County
Dear Mr. Rosborough:
Dee Freeman
Secretary
The Wilmington Regional Office received a complete, modified Stormwater Management Permit
Application for Wilmington International Airport on November 29, 2012. Staff review of the
plans and specifications has determined that the project, as proposed, will comply with the
Stormwater Regulations set forth in Title 15A NCAC 2H.1000. We are forwarding modified
Permit No. SW8 050547 dated November 29, 2012, for the construction, operation and
maintenance of the permitted BMP's and BUA associated with the subject project.
This permit is for the treatment of stormwater runoff within a designated pocket of high density
consisting of 322.34 acres in accordance with Permit No. SW8 040836, the Airport Master
Stormwater Plan. This permit modification includes the following:
1. A portion of the existing airport previously included in the drainage area of the permitted dry
detention basin is being removed. This existing area will be submitted in the future, either for
a separate BM or to be "deemed permitted" under Session Law 2012-200.
2. The drainage area boundary of the "Overall" permitted dry basin is being shifted to exclude
a previously covered area (the existing area referenced above) and is slightly increased to
bring in new drainage area.
3. Two new grassed swales are being added to provide pre-treatment for the runoff from the
added drainage area for the "Overall" condition.
4. The grassed swale plans and new drainage area plans are added to the previously
approved plans.
5. The project name is changed to remove the Phase I, II and III designation. The phases refer
to the construction of the dry detention basin, not to any particular stage of BUA
development within the airport. This permit contains design information for the "Phase I and
II" dry detention basin serving a 287.63 acre drainage area and for the °Overall" built -out dry
detention basin serving a 322.34 acre drainage area.
On August 5, 2009, the Governor signed Session Law 2009-406. This law impacts any
development approval issued by the Division of Water Quality under Article 21 of Chapter 143 of
the General Statutes, which is current and valid at any point between January 1, 2008, and
December 31, 2010. The law extends the effective period of any stormwater permit that is set to
expire during this time frame to three (3) years from its current expiration date. On August 2,
2010, the Governor signed Session Law 20.10-177, which grants an extra year for a total of four
(4) years extension. Please note that the expiration date of this permit has been adjusted to
reflect this four year extension.
Wilmington Regional Office
127 Cardinal Drive Extension, Wilmington, North Carolina 28405
Phone: [phone] FAX [phone] DENR Assistance:1-877-623-6748
Internet www.ncwaterquality.org
N a Carolina
dund
An Fmial Onnnh mllu 1 Affirmntim Arlin Fmnlnvar

State Stormwater Managemrent Qystems
Permit No. SW8 050547Mod.
This permit shall be effective from the date of issuance until June 15, 2019, and shall be subject to
the conditions and limitations as specified therein. Please pay special attention to the conditions
listed in this permit regarding the Operation and Maintenance of the BMP(s), certification of the
BMP's, procedures for changing ownership, transferring the permit, and renewing the permit.
Failure to establish an adequate system for operation and maintenance of the stormwater
management system, to certify the BMP's, to transfer the permit, or to renew the permit, will result
in future compliance problems.
If any parts, requirements, or limitations contained in this permit are unacceptable, you have the
right to request an adjudicatory hearing by filing a written petition with the Office of Administrative
Hearings (OAH). Per NCGS 143-215(e), the written petition must conform to Chapter 150B of the
North Carolina General Statutes, and must be filed with the OAH within thirty (30) days of receipt of
this permit. You should contact the OAH with all questions regarding the filing fee (if a filing fee is
required) and/or the details of the filing process at 6714 Mail Service Center, Raleigh, NC 27699-
6714, or via telephone at 919-431-3000, or visit their website at www.ncoah.com. Unless such
demands are made this permit shall be final and binding.
If you have any questions, or need additional information concerning this matter, please contact
Linda Lewis at [phone].
Sincerely,
�7*s Charles Wakild, P.E., Director
Division of Water Quality
GDS/arl: S:\WQS\Stormwater\Permits & Projects\2005\050547 HD\2012 11 permit 050547
cc: Tim Clinkscales, P.E., Paramounte Engineering
New Hanover County Building Inspections
City of Wilmington Public Services
Beth Wetherill, New Hanover County Engineering
Wilmington Regional Office Stormwater File
Page 2 of 9

State Stormwater Management Systems
Permit No. SW8 050547Mod.
STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES
DIVISION OF WATER QUALITY
STATE STORMWATER MANAGEMENT PERMIT
HIGH DENSITY DEVELOPMENT
In accordance with the provisions of Article 21 of Chapter 143, General Statutes of North
Carolina as amended, and other applicable Laws, Rules, and Regulations
PERMISSION IS HEREBY GRANTED TO
New Hanover County Airport Authority
Wilmington Intemational Airport
1740 Airport Boulevard, Wilmington, New Hanover County
FOR THE
construction, operation and maintenance of an extended dry detention basin in
compliance with the provisions of 15A NCAC 2H .1000 (hereafter collectively referred to
as the "stormwater rules') and the approved stormwater management plans and
specifications and other supporting data as attached and on file with and approved by the
Division of Water Quality and considered a part of this permit.
This permit shall be effective from the date of issuance until June 15, 2019, and shall be
subject to the following specified conditions and limitations:
I. DESIGN STANDARDS
1. This permit is effective only with respect to the nature and volume of stormwater
described in the application and other supporting data.
2. This stormwater system has been approved for the management of stormwater
runoff as described in Section 1.7 of this permit. The "Phase I and 11" stormwater
control is an extended dry detention basin that has been designed to handle the
runoff from 8,520,835 square feet of impervious area within a drainage area of
287.63 acres (12,529,107 square feet). The "Overall" condition of the dry detention
basin has been designed to handle the runoff from 9,751,185 square feet of
impervious area within a drainage area of 322.34 acres (14,041,075 so.
3. The tract will be limited to the amount of built -upon area indicated in Section 1.7 of
this permit, and per the application, the approved plans, calculations and other
supporting documentation.
4. Where an individual project within the drainage area is being leased or sold, the
stormwater collection system for that project must be located in either dedicated
common areas or easements and the final plats will be recorded showing all such
required easements.
5. The runoff from all built -upon area within the permitted drainage area of this project
must be directed into the permitted stormwater control system.
Page 3of9

State Stormwater Management Systems
Permit No. SW8 050547Mod.
6. All development projects within the permitted contributing drainage area of the
extended dry detention basin BMP must submit plans to the Division for review and
approval prior to construction. Depending on ownership, a permit modification may
or may not be required.
7. That portion of the existing airport previously included in the drainage area of the
permitted dry detention basin that is being removed, must be submitted in a future
permit application as a modification or under Session Law 2012-200.
8. The following design criteria have been provided and must be maintained in the
"Phase I and II" extended dry detention basin and in the "Overall" extended dry
detention basin.
Phase I & II Overall
a. Drainage Area, acres:
Onsite, ft2:
Offsite, ft2:
b. Total Imperious Surfaces, ft2:
C. Design Storm, inches:
d. Basin Bottom Elevation, feet:
e. TSS removal efficiency:
f. Storage Elevation, FMSL:
g. Storage Surface Area, ft2:
h. Permitted Detention Volume, ft3:
i. Seasonal High Water Table, FMSL:
j. Controlling Orifice:
k. Drawdown Time for 12.0"0 orifice, hours:
I. Receiving Stream/River Basin:
M. Stream Index Number:
n. Classification of Water Body:
287.63
322.38
12, 529,107
14,041, 075
0
0
8,520,835
9,751,185
4,552,087 @1"
4,552,087 @1"
3,968,748 @1.5"
5,199,098 @1.5"
7.0
7.0
50%
50%
13.0
13.3
506,082
602,325
1,058,112
1,274,829
6.0
6.0
12.0" 0
12.0"0
57
64
Smith Creek / Cape Fear
18-74-63
"C; Sw"
9. Tributary projects outside of the drainage area of the 2 "for -credit" grassed swales,
but inside the drainage area of the dry detention basin, must provide an additional
BMP with a sufficient TSS removal efficiency such that the total TSS removal,
including the extended dry detention basin, is at least 85%.
10. FAA requirements prohibit standing water (i.e., permanent pools) and stipulate that
the design storm must be fully drained within 48 hours. The approved BMP design
includes a low flow device but does not include a permanent pool at the low flow
outlet or sediment storage below the low flow outlet.
11. The "Phase I and II" condition will be the "permitted condition" until such time as a
project within the drainage area is proposed which shall cause the permitted
maximum amounts of drainage area and/or BUA for the Phase I & II condition to be
exceeded. Prior to construction of that project, the "Overall" condition must be
constructed and will become the permittecondition.
II. SCHEDULE OF COMPLIANCE
1. The stormwater management system shall be constructed in its entirety, vegetated
and operational for its intended use prior to the construction of any built -upon
surface. The Phase I & II condition
2. During construction, erosion shall be kept to a minimum and any eroded areas of
the system will be repaired immediately.
3. The facilities shall be constructed accordance with the conditions of this permit, the
approved plans and specifications, and other supporting data.
Page 4 of 9

State Stormwater Management Systems
Permit No. SW8 050547Mod.
Upon completion of construction, prior to issuance of a Certificate of Occupancy,
and prior to operation of this 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 this permit, the approved plans and
specifications, and other supporting documentation. Any deviations from the
approved plans and specifications must be noted on the Certification. A
modification may be required for those deviations.
The permittee shall at all times provide the operation and maintenance necessary
to assure the permitted stormwater system functions at optimum efficiency. The
approved Operation and Maintenance Plan must be followed in its entirety and
maintenance must occur at the scheduled intervals including, but not limited to:
a. Semiannual scheduled inspections (every 6 months).
b. Sediment removal.
C. Mowing and revegetation of slopes and the vegetated filter.
d. Immediate repair of eroded areas.
e. Maintenance of all slopes in accordance with approved plans and
specifications.
f. Debris removal and unclogging of outlet structure, orifice device, flow
spreader, catch basins and piping.
g. Access to the outlet structure must be available at all times.
6. Records of maintenance activities must be kept and made available upon request
to authorized personnel of DWQ. The records will indicate the date, activity, name
of person performing the work and what actions were taken.
7. If the stormwater system was used as an Erosion Control device, it must be
restored to design condition prior to operation as a stormwater treatment device,
and prior to occupancy of the facility.
8. Access to the pemitted stormwater facilities shall be maintained via appropriate
easements (as required) at all times.
9. The permittee shall submit to the Director and shall have received approval for
revised plans, specifications, and calculations prior to construction, for any
modification to the approved plans, including, but not limited to, those listed below:
a. Any revision to any item shown on the approved plans, including the
stormwater management measures, built -upon area, details, etc.
b. Redesign or addition to the approved amount of built -upon area or to the
drainage area.
C. Further subdivision, acquisition, lease or sale of all or part of the project
area.
d. Construction of any future built -upon area within the drainage area.
e. Filling in, altering, or piping of any vegetative conveyance shown on the
approved plan.
10. The Director may notify the permittee when the permitted site does not meet one or
more of the minimum requirements of the permit. Within the time frame specified in
the notice, the permittee shall submit a written time schedule to the Director for
modifying the site to meet minimum requirements. The permittee shall provide
=een
of revised plans and certification in writing to the Director that the changes
made.
III. GENERAL CONDITIONS
1. The issuance of this permit does not preclude the Permittee from complying with
any and all statutes, rules, regulations, or ordinances, which may be imposed by
other government agencies (local, state, and federal) having jurisdiction.
Page 5 of 9

State Stormwater Management Systems
Permit No. SW8 050547Mod.
2. This permit is not transferable to any person or entity except after notice to and
approval by the Director. At least 60 days prior to a change of ownership, or a
name change of the owner or of the project, or a mailing address change, the
permittee must submit a completed and signed Name/Ownership Change Form to
the Division of Water Quality, accompanied by the documentation listed on the
form. The approval of this request will be considered on its merits and may or may
not be approved. The project must be inspected by the Division and must be
determined to be in compliance with the permit conditions prior to the Division
approving the transfer request.
3. Failure to abide by the conditions and limitations contained in this permit may
subject the Permittee to enforcement action by the Division of Water Quality, in
accordance with North Carolina General Statute 143-215.6A to 143-215.6C.
4. In the event that the facilities fail to perform satisfactorily the Permittee shall take
immediate corrective action, including those as may be required by this Division,
such as the construction of additional or replacement stormwater management
systems.
5. The permittee grants DENR Staff permission to enter the property during normal
business hours for the purpose of inspecting all components of the permitted
stormwater management facility.
6. The permit may be modified, revoked and reissued or terminated for cause. The
filing of a request for a permit modification, revocation and reissuance or
termination does not stay any permit condition.
7. Unless specified elsewhere, permanent seeding requirements for the stormwater
control must follow the guidelines established in the North Carolina Erosion and
Sediment Control Planning and Design Manual.
8. Approved plans and specifications for this project are incorporated by reference
and are enforceable parts of the permit. A copy of the approved plans and
specifications shall be maintained on file by the Permittee at all times.
9. The permittee shall submit a permit renewal application and fee at least 180 days
prior to the expiration date of this permit.
Permit modified and reissued this the 29th day of November 2012
NORTH CAROLINA ENVIRONMENTAL MANAGEMENT COMMISSION
Division of Water Quality
By Authority of the Environmental Management Commission
Page 6 of 9

State Stormwater Management Systems
Permit No. SW8 050547Mod.
Wilmington International Airport
Stormwater Permit No. SW8 050547Mod
New Hanover County
Designer's Certification
1, , as a duly registered in the
State of North Carolina, having been authorized to observe (periodically/ weekly/ full time)
the construction of the project,
(Project)
for (Project Owner) hereby state that, to the
best of my abilities, due care and diligence was used in the observation of the project
construction such that the construction was observed to be built within substantial
compliance and intent of the approved plans and specifications.
The checklist of items on page 2 of this form is included in the Certification.
Noted deviations from approved plans and specification:
Signature
Registration Number
Date
SEAL
Page 7 of 9

State Stormwater Management Systems'
Permit No. SW8 050547Mod.
Certification Requirements:
.1. The drainage area to the system contains approximately the permitted
acreage.
2. The drainage area to the system contains no more than the permitted
amount of built -upon area.
.3. All the built -upon area associated with the project is graded such that the
runoff drains to the system.
4. All drainage within the permitted contributing drainage area is directed into
the system.
5. The outlet/bypass structure elevations are per the approved plan.
6. The outlet structure is located per the approved plans.
7. A trash rack is provided on the outlet/bypass structure.
8. All slopes are grassed with permanent vegetation.
9. Vegetated slopes are no steeper than 3:1.
10. The inlets are located per the approved plans and do not cause short-
circuiting of the system.
11. The permitted amounts of surface area and/or volume have been provided.
12. Required drawdown device is correctly located and sized per the approved
plans.
13. All required design depths are provided.
14. All required parts of the system are provided, such as pretreatment devices,
outlet structure and/or forebay.
15. The required system dimensions are provided per the approved plans.
16. The maximum drainage area and/or built -upon area have not been
exceeded for the "Phase I & II" condition.
cc: NCDENR-DWQ Regional Office
New Hanover County Building Inspections
Page 8 of 9

State Stormwater Management Systems
Permit No. SW8 050547Mod.
The master permit tables for Phase I and II were added to the permit on September 20,
2010, as part of the review for the modification to SW8 060515.
Phase III was added on October 26, 2011.
A modification to the tables was added on November 27, 2012. Phasing refers to the dry
basin, not to the airport BUA.
Master Permit No. SW8 050547 Phase I & II Basin
Startina New BUA balance = 8,520,835-4,552 087 = 3,968,748
Mod/Offsite
Permit No.
Date Issued
Offsite Project Name
Proposed
BUA
Remaining
BUA
SW8 050801
General Aviation Apron
Expansion
151,589
3,817,159
SW8 060326
Air Wilmington FBO
Building
196,725
3,620,434
SW8 060515
Credit Card Parking Lot
225,722
3,394,712
SW8 050547
10/28/2009
ILM Phase I and Phase 11
for gravel roads
15,843
3,378,869
SW8 050547
11/27/2012
Delineate a new overall
DA, increase the max
BUA allowed.
0
3,378,869
Master Permit No. SW8 050547 Overall Basin
Offsite Permit No.
Date Issued
Offsite Project Name
Proposed
BUA
Remaining
BUA
i i
i
I
I
I
Page 9 of 9

DWQ USE ONLY
Date Received
Fee Paid
Zermit Number
10100. -3a
1 _sA DAD
Applicable Rules: ❑ Coastal SW -1 5 ❑ Coastal SW - 2008 ❑ Ph II - Post Construction
(select all that apply) ❑ Non -Coastal SW- HQW/ORW Waters ❑ Universal Stormwater Management Plan
❑ Other WQ M mt Plan:
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
This form may be photocopied for use as an original
I. GENERAL INFORMATION
1. Project Name (subdivision, facility, or establishment name - should be consistent with project name on plans,
specifications, letters, operation and maintenance agreements, etc.):
Wilmington International Airport
2. Location of Project (street address):
1740 Airport Boulevard
City:Wilmington County:New Hanover Zip:28405
3. Directions to project (from nearest major intersection):
South of the intersection of Gardner Drive and Airport Blvd at the Wilmington International Airport
4. Latitude:34° 15' 50" N Longitude:770 54' 51" W of the main entrance to the project.
II. PERMIT INFORMATION:
1. a. Specify whether project is (check one): ❑New ®Modification
b. If this application is being submitted as the result of a modification to an existing permit, list the existing
permit numberSW8 050547 , its issue date (if known) and the status of
construction: ❑Not Started ❑Partially Completed* ® Completed* *provide a designer's certification
2. Specify the type of project (check one): =- Z(V Z0I I
❑Low Density ®High Density ❑Drains to an Offsite Stormwater System ❑Other
3. If this application is being submitted as the result of a previously returned application or a letter from DWQ
requesting a state stormwater management permit application, list the stormwater project number, if
assigned, and the previous name of the project, if different than currently
proposed,
4. a. Additional Project Requirements (check applicable blanks; information on required state permits can be
obtained by contacting the Customer Service Center at 1-877-623-6748):
❑CAMA Major Sedimentation/Erosion Control: _
❑NPDES Industrial Stormwater ❑404/401 Permit: Proposed Impacts
ac of Disturbed Area
b. If any of these permits have already been acquired please provide the Project Name, Project./Permit Number,
issue date and the type of each permit:
OCT U .9 Z012
BY:
Form SWU-101 Version 07Jun2010 Page 1 of 6

III. CONTACT INFORMATION
1: a. Print Applicant / Signing Official's name and title (specifically the developer, property owner, lessee,
designated government official, individual, etc. who owns the Project):
Ar)nlicant/OrLranization-New HannvPr C'nnnty Airnnrf Ai,+hnrifix ..
Signing Official &
b. Contact information for person listed in item 1a above:
Street Address:1740 Airport Boulevard
City:Wilmingion State:NC Zip:28405
Mailing Address (if applicable):
City: State: Zi
Phone: 910 ) 341-4333 Fax: (910 ) 341' 5
[e-mail]
c. Please check the appropriate box. The applicant listed above is:
® The property owner (Skip to Contact Information, item 3a)
❑ Lessee* (Attach a copy of the lease agreement and complete Contact Information, item 2a and 2b below)
❑ Purchaser* (Attach a copy of the pending sales agreement and complete Contact Information, item 2a and
2b below)
❑ Developer* (Complete Contact Information, item 2a and 2b below.)
2. a. Print Property Owner's name and title below, if you are the lessee, purchaser or developer. (This is the
person who owns the property that the project is located on):
Property Owner/Organization:
Signing Official &
b. Contact information for person listed in item 2a above:
Street Address:
City: State: Zip:
Mailing Address (if applicable
City:
Phone: ( )
Email:
State: Zip: _.
Fax: ( 1
3. a. (Optional) Print the name and title of another contact such as the project's construction supervisor or other
person who can answer questions about the project:
Other Contact Person/Organization:
Signing Official & Title:
b. Contact information for person listed in item 3a above:
Mailing Address:
City: State:
Phone: ( ) Fax: ( )
Email:
4. Local jurisdiction for building permits: New Hanover Court
Point of Contact:lay Graham Phone #: (910 ) 798-7175
OCTvFil
o s zo�z
Form SWU-101 Version 07Jun2010 Page 2 of 6

IV. PROJECT INFORMATION
1. In the space provided below, briefly summarize how the stormwater runoff will be treated.
The extended dry basin will used to treat stormwater.
2. a. If claiming vested rights, identify the supporting documents provided and the date they were approved:
❑ Approval of a Site Specific Development Plan or PUD Approval Date:
❑ Valid Building Permit Issued Date:
❑ Other: Date:
b.If claiming vested rights, identify the regulation(s) the project has been designed in accordance with:
® Coastal SW -1995 ❑ Ph II - Post Construction
3. Stormwater runoff from this project drains to the Cape Fear River basin.
4. Total Property Area: 1620.8 acres 5. Total Coastal Wetlands Area: acres
6. Total Surface Water Area: acres
7. Total Property 2Ara (4) - Total Coastal Wetlands Area (5) - Total Surface Water Area (6) = Total Project
Area+: 22• / acres
+ Total project area shall be calculated to exclude the following the normal pool of impounded structures, the area
between the banks of streams and rivers, the area below the Normal High Water (NHM line or Mean High Water
(MHW) line, and coastal wetlands landward from the NHW (or MHM line. The resultant project area is used to
calculate overall percent built upon area (BUA). Non -coastal wetlands landward of the NHW (or AlW line may
be included in the total project area.
8. Project percent of impervious area: (Total Impervious Area / Total Project Area) X 100 = 69.4 %
9. How many drainage areas does the project have?1 (For high density, count 1 for each proposed engineered
stormwater BMP. For low density and other projects, use 1 for the whole property area)
10. Complete the following information for each drainage area identified in Project Information item 9. If there
are more than four drainage areas in the project, attach an additional sheet with the information for each area
provided in the same format as below.
Basin Information
Drainage Area 1
Drainage Area _
Drainage Area _
Drainage Area
Receiving Stream Name
Smith Creek
_
Stream Class *
C,Sw
Stream Index Number *
see attachment
Total Drainage Area (sf)
On -site Drainage Area (sf)
Off -site Drainage Area (sf)
0
Proposed Impervious Area** s
% Impervious Area** total
Impervious" Surface Area
Drainage Area 1
Drainage Area _
Drainage Area _
Drainage Area
On -site Buildings/Lots (sf)
-° LOV
_
On -site Streets (sf)
tea. MUIA
On -site Parking (sf)
44La, tv
On -site Sidewalks (sf)
Other on -site (so
r
Future (sf)
Off -site (so
Existing BUA*** (sf)
Total (sf):
Stream Class and Index Number can be determined at: littp.aortal.itcdenr.org/web/wq&s/csu/classifications
Im ervious area is defined as the built upon area including, but not limited to, buildings, road-., p parking areas,
sidewalks, gravel areas, etc.
OCT 0.9 2012
Form SWU-101 Version 07]un2010 Page 3 of 6 PV.

'Report only that amount of existing BUA that will remain after development. Do not report any existing BUA that
is to be removed and which will be replaced by new BUA.
11. How was the off -site impervious area listed above determined? Provide documentation. Tributary area is
entirely on -site
Proiects in Union County: Contact DWQ Central Ojfce staff to check if the project is located within a Threatened &
Endangered Species watershed that may be subject to more stringent stormwater requirements as per NC,4C 02B . 0600.
V. SUPPLEMENT AND O&M FORMS
The applicable state stormwater management permit supplement and operation and maintenance (O&M) forms
must be submitted for each BMP specified for this project. The latest versions of the forms can be downloaded
from http://portal.ncdenr.org/web/wq/ws/su/bmj2-manual.
VI. SUBMITTAL REQUIREMENTS
Only complete application packages will be accepted and reviewed by the Division of Water Quality (DWQ).
A complete package includes all of the items listed below. A detailed application instruction sheet and BMP
checklists are available from http://portal.ncdenr.org/web/wq/ws/su/statesw/forms dots. The complete
application package should be submitted to the appropriate DWQ Office. (The appropriate office may be
found by locating project on the interactive online map at http:/ /12ortal.ncdei-Lr.org/web/wq./ws/su/maps.)
Please indicate that the following required information have been provided by initialing in the space provided
for each item. All original documents MUST be signed and initialed in blue ink. Download the latest versions
for each submitted application package from ht!2://portal.ncdenr.org/web/wq/ws/su/statesw/forms does.
Initials
1. Original and one copy of the Stormwater Management Permit Application Form.
2. Original and one copy of the signed and notarized Deed Restrictions & Protective Covenants A4
Form. (if required as per Part VII below)
3.
Original of the applicable Supplement Form(s) (sealed, signed and dated) and O&M
r�G
agreement(s) for each BMP. S
4.
Permit application processing fee of $505 payable to NCDENR. (For an Express review, refer to
C-
http:/ /www.envhel�org/pages/onestol2express.html for information on the Express program
and the associated fees. Contact the appropriate regional office Express Permit Coordinator for
additional information and to schedule the required application meeting.)
5.
A detailed narrative (one to two pages) describing the stormwater treatment/management
forC
6.
A USGS map identifying the site location. If the receiving stream is reported as class SA or the
TG. e--
receiving stream drains to class SA waters within 1/2 mile of the site boundary, include the 1/2
mile radius on the map.
7.
Sealed, signed and dated calculations.
etr- C—
8.
Two sets of plans folded to 8.5" x 14" (sealed, signed, & dated), including:
a. Development/Project name.
b. Engineer and firm.
c. Location map with named streets and NCSR numbers.
d. Legend.
e. North arrow.
f. Scale.
g. Revision number and dates.
h. Identify all surface waters on the plans by delineating the normal pool elevation of
impounded structures, the banks of streams and rivers, the MHW or NHW line of tidal
waters, and any coastal wetlands landward of the MHW or NHW lines.
• Delineate the vegetated buffer landward from the normal pool elevation of impounded
structures, the banks of streams or rivers, and the MHW (or NHW) of tidal waters.
i. Dimensioned property/project boundary with bearings & distances.
j. Site Layout with all BUA identified and dimensioned.
k. Existing contours, proposed contours, spot elevations, finished floor elevations.
1. Details of roads, drainage features, collection systems, and stormwater control measures.
m. Wetlands delineated, or a note on the plans that none exist. (Must be delineated by a
qualified person. Provide documentation of qualifications and identify the person who
made the determination on the plans.'��,%�;�.
n. Existing drainage (including off -site), drainage easements, pipe sizes, runoff calculations.
o. Drainage areas delineated (included in the main set of plans, not as a separate document).
0 C T 0 9 2012
p. Vegetated buffers (where required).
Form SWU-101 Version 07Jun2010 Page 4 of 6
j
LAY'

. 9. Copy of any applicable soils report with the associated SHWT elevations (Please identify 1
elevations in addition to depths) as well as a map of the boring locations with the existing
elevations and boring logs. Include an 8.5"xll" copy of the NRCS County Soils map with the
project area clearly delineated. For projects with infiltration BMPs, the report should also
include the soil type, expected infiltration rate, and the method of determining the infiltration rate.
(Infiltration Devices submitted to WiRO: Schedule a site visit for DWQ to verify the SHWT prior
to submittal, [phone].)
10. A copy of the most current property deed. Deed book: see attached Page No:
11. For corporations and limited liability corporations (LLC): Provide documentation from the NC !ram F+
Secretary of State or other official documentation, which supports the titles and positions held
by the persons listed in Contact Information, item la, 2a, and/or 3a per NCAC 2H.1003(e). The
corporation or LLC must be listed as an active corporation in good standing with the NC
Secretary of State, otherwise the application will be returned.
httg://www.secretary.state.nc.us/Corporations/CSearch.asl2x
VII. DEED RESTRICTIONS AND PROTECTIVE COVENANTS
For all subdivisions, outparcels, and future development, the appropriate property restrictions and protective
covenants are required to be recorded prior to the sale of any lot. If lot sizes vary significantly or the proposed
BUA allocations vary, a table listing each lot number, lot size, and the allowable built -upon area must be provided
as an attachment to the completed and notarized deed restriction form. The appropriate deed restrictions and
protective covenants forms can be downloaded from
http: / /portal.ncdenr.org/web/wq/ws/su/statesw/forms does. Download the latest versions for each submittal.
In the instances where the applicant is different than the property owner, it is the responsibility of the property
owner to sign the deed restrictions and protective covenants form while the applicant is responsible for ensuring
that the deed restrictions are recorded.
By the notarized signature(s) below, the permit holder(s) certify that the recorded property restrictions and
protective covenants for this project, if required, shall include all the items required in the permit and listed
on the forms available on the website, that the covenants will be binding on all parties and persons claiming
under them, that they will run with the land, that the required covenants cannot be changed or deleted
without concurrence from the NC DWQ, and that they will be recorded prior to the sale of any lot.
VIII. CONSULTANT INFORMATION AND AUTHORIZATION
Applicant: Complete this section if you wish to designate authority to another individual and/or firm (such as a
consulting engineer and/or firm) so that they may provide information on your behalf for this project (such as
addressing requests for additional information).
Consulting Engineer:Tim Clinkscales
Consulting Firm: Paramounte Engineering rr'' �
Mailing Address:5911 Oleander Drive CY�j iT&, [ 0
City:Wilrnington
Phone: (910 ) 791-6707
Email:
State:NC Zip:28403
Fax: (910 ) 791-6760
IX. PROPERTY OWNER AUTHORIZATION (if Contact Information, item 2 has been filled out, complete this
section)
I, (print or type name of person listed in Contact Information, item 2a) . certify that I
own the property identified in this permit application, and thus give permission to (print or type name of person
listed in Contact Information, item 1a) with (print or type name of organization listed in
Contact Information, item 1a) to develop the project as currently proposed. A copy of
the lease agreement or pending property sales contract has been provided with the submittal, which indicates the
party responsible for the operation and maintenance of the stormwater system.
Form SWU-101 Version 07Jun2010 Page 5 of 6
r R-1 C I IVE
03CT 2012
Y':

As the legal p.operiy, owner I acknowledge, understand, and agree by my signature below, that if my designated
agent (entity listed in Contact Information, item 1) dissolves their company and/or cancels or defaults on their
lease agreement, or pending sale, responsibility for compliance with the DWQ Stormwater permit reverts back to
me, the property owner. As the property owner, it is my responsibility to notify DWQ immediately and submit a
completed Name/Ownership Change Form within 30 days; otherwise I will be operating a stormwater treatment
facility without a valid permit. I understand that the operation of a stormwater treatment facility without a valid
permit is a violation of NC General Statue 143-215.1 and may result in appropriate enforcement action including
the assessment of civil penalties of up to $25,000 per day, pursuant to NCGS 143-215.6.
Signature: Date:
I, 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 application for a
stormwater permit. Witness my hand and official seal,
SEAL
My commission expires
X. APPLICANT'S CERTIFICATION
I, (print or type name of person listed in Contact Information, item 1a) Iulie Wilsey
certify that the information included on this permit application form is, to the best of my knowledge, correct and
that the project will be constructed in conformance with the approved plans, that the required deed restrictions
and protective covenants will be recorded, and that the proposed project complies with the requirements of the
applicable s mJ:lr
ru (u'nder 15A NCAC 2H .1000, SL 2006-246 (Ph. II — Post Construction) or SL 2008-211.
Signature: W (�
� Date: �� � t � !
I, "RU S� / ► Ls 1f1 S a Notary Public for the State_ of No, -CA res V,, County of
��// rW '�I
1Y �' � ''� � , do hereby certify that �i�.t i i' f't • w i• I Se y personally appeared
before me this day of DC41 6t- and ac wledge th due execution of the application for a
n� o
stormwater permit. Witness my hand and official seal, 1 V A4A4
Z9�bo&B 00
ER C
�/MNIINIlO
SEAL
My commission expires�I
OCT 0;9 201Z
Form SWU-101 Version 07Jun2010 Page 6 of 6

Permit Name: _5
5�j,,3(e (to be provided by DWQ)
-Drainages.-Area Number:_
Grassed Swale 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.
Important maintenance procedures:
— The drainage area of the grassed swale will be carefully managed to reduce the
sediment load to the grassed swale.
— After the first-time fertilization to establish the grass in the swale, fertilizer will
not be applied to the grassed swale.
The grassed swale will be inspected once a quarter. Records of operation and
maintenance will be kept in a known set location and will 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 theproblem:
The entire length of the
Trash/debris is present.
Remove the trash/debris.
swale
Areas of bare soil and/or
Regrade the soil if necessary to
erosive gullies have formed.
remove the gully, and then re -sod
(or plant with other appropriate
species) and water until established.
Provide lime and a one-time
fertilizer application.
Sediment covers the grass at
Remove sediment and dispose in an
the bottom of the swale.
area that will not impact streams or
BMPs. Re -sod if necessary.
Vegetation is too short or too
Maintain vegetation at a height of
long.
approximately six inches.
The receiving water
Erosion or other signs of
Contact the NC Division of Water
damage have occurred at the
Quality 401 Oversight Unit at 919-
outlet.
733-1786.
OCT 0 9 2012
'BY:
Form SW401-Grassed Swale O&M-Rev.3 Page 1 of 2

Permit Number: ` (y '? OSU 5¢7
(to be provided by DWQ)
I 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:Wilmington International Airport - Pretreatment Swales
BMP drainage area number:Pre Treatment Swale #1
Print name:Julie Wilsey
Title:Douty Director - New Hanover County Airport Authority
Address:1740 Airport Blvd Wilmington NC 28405
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, '_R0 X M 1 F� ayl S , a Notary Public for the State of
Ner`l-k lacryI Irv, , County of KkQ h.n0,- , do hereby certify that cl
A. personally appeared before me this b
day of Oc4b bee , Soo I a- , and acknowledge the due execution of the
forgoing grassed swale maintenance requirements. Witness my hand and official seal,
,�NNIIIIIIINyfff/'
ara"c�E M.
41 ,PTAMM
,2 =
}mot Z,
S`
yNoJ13
SEAL
My commission expires taliq
Form SW401-Grassed Swale O&M-Rev.3
ft"' M f�3a4na
OCT 0 9 2012
Page 2 of 2 - -

Permit Name:
SW2k (to be provided DWQ)
•Drainage-Area Number: ;2
Grassed Swale 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.
Important maintenance procedures:
— The drainage area of the grassed swale will be carefully managed to reduce the
sediment load to the grassed swale.
— After the first-time fertilization to establish the grass in the swale, fertilizer will
not be applied to the grassed swale.
The grassed swale will be inspected once a quarter. Records of operation and
maintenance will be kept in a known set location and will 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 theproblem:
The entire length of the
Trash/debris is present.
Remove the trash/debris.
swale
Areas of bare soil and/or
Regrade the soil if necessary to
erosive gullies have formed.
remove the gully, and then re -sod
(or plant with other appropriate
species) and water until established.
Provide lime and a one-time
fertilizer application
Sediment covers the grass at
the bottom of the swale.
Remove sediment and dispose in an
area that will not impact streams or
BMPs. Re -sod if necessary.
Vegetation is too short or too
Maintain vegetation at a height of
long.
approximately six inches.
The receiving water
Erosion or other signs of
Contact the NC Division of Water
damage have occurred at the
Quality 401 Oversight Unit at 919-
outlet.
733-1786.
OCT 0 9 2012
Form SW401-Grassed Swale O&M-Rev.3 Page 1 of 2

Permit Number: 5v 10 So S -2
(to be provided by DWQ)
I 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:Wilmington International Airport - Pretreatment Swales
BMP drainage area number:Pre Treatment Swale #2
Print name:Julie Wilsey
Title:Depuuty Director - New Hanover County Airport Authority
Address:1740 Airport Blvd Wilmington NC 28405
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, Tyst W I IJ'tV, , a Notary Public for the State of
f 1 dY4) Lra )In&, , County of f4-unDve4 , do hereby certify that
J �J.'►,- A. 0 ,15e u personally appeared before me this
day of DCio ja e r - , �1 a , and acknowledge the due execution of the
forgoing grassed swale maintenance requirements. Witness my hand and official seal,
N�WENIINp%VArO".
Ap O�•
� a
�v �rr
"EBR��G
C�
O%•- 11II11I�I -
SEAL
My commission expires y hn Iig
OCT 0 9 Z012
Form SW401-Grassed Swale O&M-Rev.3 Page 2 of 2

Permit Number:
(to be provided by DWQ)
WDEHR STORMWATER MANAGEMENT PERMIT APPLICATION FORM Y
401 CERTIFICATION APPLICATION FORM
GRASSED SWALE SUPPLEMENT
This form must be filled out, printed and submitted.
The Required Items Checklist (Part Ill) must also be filled out, printed and submitted along with all of the required information.
L PROJECT INFORMATION
Project name
Contact name
Phone number
Date
Drainage area number
(I. DESIGN INFORMATION
Site Characteristics
ILM - Business Park Master 5torrnwater
Chris Millis, PE
910-791-6707
October 5, 2012
PRE-TREATMENT AREA #1 Iropw a l
Drainage area
5,032,157,00 ftz
Impervious area
3,270,484.00 fe
Percent impervious
65.0% %
Design rainfall depth
n/a inch
Peak Flow Calculations
10-yr storm runoff depth
7.00
in
10-yr storm intensity
2.38
in/hr
Post -development 10-yr storm peak flow
184.00
felsec
Velocity
Maximum non -erosive velocity (peak 10-year storm)
5.00 ft/sec
Soil characteristics (enter "x" below)
Sand/silt (easily erodible)
X
Clay mix (erosion resistant)
Grass Type (enter "x" below)
66tmuda ��rfifli4 `i�ff
x
Tall fescue
Bahiagrass
Kentucky bluegrass
_
Grass -legume mixture
Swale type: Fill out one of the options below:
Option 1: Curb Outlet Swale:
N
(Y or N)
Maximum velocity
Side slopes
:1
Swale length
ft
Option 2: Convevance Swale, Seeking Pollutant Credit:
Y
(Y or N)
Maximum velocity for 10-yr storm
1.00
ft/sec OK
Side slopes
5.00
:1 OK
Swale length
150.00
ft OK
NOV 0 2 2012
Form SW401-Grassed Swale-Rev.3 Parts I and II. Project Design Summary, Page 1 of 2

Permit Number.
(to be provided by DWG)
Swale Characteristics
Swale Shape: Enter an "x" in the appropriate cell below:
Trapezoidal
Parabolic
V-shaped
Width of the bottom of the swale
22.00 ft
Width of the top of the swale
152.00 ft
Additional Information
Is the swale sized for all runoff from ultimate build -out?
Y (Y or N)
OK
Is the BMP located in a proposed drainage easement with a
recorded access easement to a public Right of Way (ROW)?
Y (Y or N)
OK
What is the distance from the bottom of the swale to the SHWT?
5.00 ft
OK
What is the ground level elevation?
24.00 fmsl
What is the elevation of the bottom of the swale?
11.00 fmsl
What is the SHWT elevation?
6.00 fmsl
What is the longitudinal slope of the swale?
0.02 %
OK
What is the depth of freeboard?
5-06 ft
OK
NOV p 2 2Oi2
Form SW401-Grassed Swale-Rev.3
Parts I and II. Project Design Summary, Page 2 of 2

Permit No:
(to be assigned by DWQ)
!!X REQUIRE© ITEMS 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.
Initials Pagel Plan
Sheet No.
C w�1n 1. Plans (1" = 50' or larger) of the entire site showing:
Design at ultimate build -out,
Off -site drainage (if applicable),
- Delineated drainage basins (include Rational C coefficient per basin),
- Swale dimensions (width, length, depth),
- Maintenance access,
- Proposed drainage easement and public right of way (ROW),
- Grass species, and
- Boundaries of drainage easement.
�— 2. Plan details (1" = 50' or larger) for the grassed swale showing:
- Swale dimensions (width, length, depth),
- Maintenance access,
Proposed drainage easement and public right of way (ROW),
Design at ultimate build -out,
- Grass species,
- Off -site drainage (if applicable),and
- Boundaries of drainage easement.
rw vy\ C— �0 3. Section view of the grassed swale (1" = 20' or larger) showing:
Side slopes,
Longitudinal slope,
Freeboard
- Swale dimensions, and
- SHWT level(s)
Chi ( 4. Supporting calculations (including maximum velocity calculations for applicable storms)
yttiry' 5. A copy of the signed and notarized operation and maintenance (0&M) agreement.
N� 6. A copy of the deed restrictions (if required).
OCT u 9 2012
SW401-Grassed Swale-Rev.3 Part III, Page 1 of 1

Permit Number: ?0M54%
(to be provided by DWQ)
MCDENR
Y
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
GRASSED SWALE SUPPLEMENT
This form must be filled out, printed and submitted.
The Required Items Checklist (Part Ill) must also be filled out, printed and submitted along with all of the required information.
1. PROJECT INFORMATION
Project name
Contact name
Phone number
Date
Drainage area number
IL DESIGN INFORMATION
Site Characteristics
ILM - Business Park Master Stormwater
Chris Millis, PE
910-791-6707
October 5, 2012
PRE-TREATMENT AREA #2
Drainage area
5,095,6480 fe
Impervious area
3;833,280.00 fe
Percent impervious
75.2% %
Design rainfall depth
n/a inch
Peak Flow Calculations
10-yr storm runoff depth
7.00
in
10-yr storm intensity
1.96
in/hr
Post -development 10-yr storm peak flow
17200
fe/sec
Velocity
Maximum non -erosive velocity (peak 10-year storm)
5.00 ft/sec
Soil characteristics (enter 'Y' below)
Sand/silt (easily erodible)
X
Clay mix (erosion resistant)
Grass Type (enter Y below)
Bermuda {� W""Af
x
Tall fescue
Bahiagrass
Kentucky bluegrass
Grass -legume mixture
Swale type: Fill out one of the options below:
Option 1: Curb Outlet Swale:
N
(Y or N)
Maximum velocity
Side slopes
:1
Swale length
ft
Option 2: Convevance Swale, Seekinq Pollutant Credit:
Y
(Y or N)
Maximum velocity for 10-yr storm
0,98
ft/sec OK
Side slopes
500
:1 OK
Swale length
150.00
ft OK
JECEIVE�
NOV 0 2 2012
HY: _
Form SW401-Grassed Swale-Rev.3
Parts I and II. Project Design Summary, Page 1 of 2

Permit Number.5(A) t?0-50 57
(to be provided by DWQ)
Smie` Characteristics
Swale Shape: Enter an Y in the appropriate cell below:
Trapezoidal
Parabolic
V-shaped
Width of the bottom of the swale
2200.tt
Width of the top of the Swale
152.00 ft
Additional Information
Is the swale sized for all runoff from ultimate build -out?
Y (Y or N)
OK
Is the BMP located in a proposed drainage easement with a
recorded access easement to a public Right of Way (ROW)?
Y (Y or N)
OK
What is the distance from the bottom of the swale to the SHWT?
5.00 ft
OK
What is the ground level elevation?
24 00 fmsl
What is the elevation of the bottom of the swale?
11.00 fmsl
What is the SHWT elevation?
6.00 fmsf
What is the longitudinal slope of the swale?
0.02 %
OK
What is the depth of freeboard?
5 00 ft
OK
NOV 0 2 202
Form SW401-Grassed Swale-Rev.3
Parts i and II. Project Design Summary, Page 2 of 2

Permit No:
_ (to be assigned by DWQ)
14111. gQUIRED ITEMS 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,
Initials Pagel Plan
Sheet No.
(ftm C—�M 0 1. Plans (1" = 50' or larger) of the entire site showing:
Design at ultimate build -out,
- Off -site drainage (if applicable),
- Delineated drainage basins (include Rational C coefficient per basin),
- Swale dimensions (width, length, depth),
- Maintenance access,
Proposed drainage easement and public right of way (ROW),
- Grass species, and
- Boundaries of drainage easement.
2. Plan details (1" = 50' or larger) for the grassed swale showing:
Swale dimensions (width, length, depth),
Maintenance access,
Proposed drainage easement and public right of way (ROW),
Design at ultimate build -out,
Grass species,
- Off -site drainage (if applicable),and
Boundaries of drainage easement.
3. Section view of the grassed swale (1" = 20' or larger) showing:
Side slopes,
- Longitudinal slope,
Freeboard
- Swale dimensions, and
- SHWT level(s)
_
4. Supporting calculations (including maximum velocity calculations for applicable storms)
5. A copy of the signed and notarized operation and maintenance (0&M) agreement.
�wr/1 6. A copy of the deed restrictions (if required)
OCT U 9 2012
SW401-Grassed Swale-Rev.3 Part III, Page 1 of 1

Permit No.
(tent he provided by DWfy
AWSTORMWATER MANAGEMENT PERMIT APPLICATION FORM
WDENR 401 CERTIFICATION APPLICATION FORM
DRY EXTENDED DETENTION BASIN SUPPLEMENT
This form must be filled out, printed and submitted.
The Required Items Checklist (Part Ill) must be printed, filled out and submitted along with all the required information.
I. PROJECT INFORMATION
Project name Wilmington International Airport
Contact person Jon W Rosborough, Airport Director
Phone number 910-431-4333 ext 1001
Data 11/29/2012
Drainage area number 1(Phase I & II Condition)
II. DESIGN INFORMATION
Site Characteristics
Drainage area 12,529,106.00 fe
Impervious area 8,520,834.00 fe
% Impervious 0.68
Design rainfall depth 1.23 in 4,552,087 (111 3,968,747 (1-5")
Peak Flow Calculations
1-yr, 24-hr rainfall depth
3.83
in
Rational C, pre -development
72.00
(unitless)
Rational C, post -development
88.00
(unitless)
Rainfall intensity: 1-yr, 24-hr storm
0.76
in/hr
Pre -development 1-yr, 24-hr peak flow
�- 75.00
ielsec
Post -development 1-yr, 24-hr peak flow
173.00
Osec
Pre/Post 1-yr, 24-hr peak control
98.00
fOlsec
Storage Volume: Non -SA Waters
Minimum required volume
1,041,133.00
ft
Provided volume
1,058,l i2.00
fe OK
Sediment storage volume provided
206,459.00
fe Increase to at least 25% of volume provided
Storage Volume: SA Waters
1.5" runoff volume
nla
Pre -development 1-yr, 24-hr runoff volume
_
nla
_fl3
fl3
Post -development 1-yr, 24-hr runoff volume
nla
fe
Minimum required volume
#VALUE!
fe
Provided volume
We
fl3 #VALUE!
Sediment storage volume provided
nla
ft #VALUE!
Basin Design Parameters
Drawdown time
2.37
days
OK
SHWT elevation
6.00
fmsl
Basin bottom elevation
7.00
fmsi
Raise basin bottom, Must be at least 2-ft above SHWT
Storage elevation
13.00
fmsl
Basin side slopes
4.0
:1
OK
Top elevation
20.00
fmsl
Too deep, maximum depth of 10-feet allowed
Freeboard provided
7.00
ft
OK
Basin Bottom Dimensions
Basin length
1,350.00
ft
RECEIVED
Basin width
450.00
ft
Length to width ratio
3.00
:1
OK
N O V 2 9 2012
BY:
Form SW401-Dry Extended Detention Basin-Rev.3
Parts I. & It. Design Summary, Page 1 of 2

Additional Information
Total runoff volume captured by basin
Forebay provided
Is basin in a recorded drainage easement?
Does basin capture all runoff at ultimate build -out?
Is a sediment depth indicator included?
Does the basin include'a drain?
291.49 ac-in
Forebay Is required
y (Y or N)
y (Y or N)
OK
y (Y or N)
OK
y (Y or N)
OK
y (Y or N)
OK
Permit No.
(to be provided by DWQ)
Additional Information per comment letter dated October 6, 2009:
a. Orifice Size: 1211
b. Orifice Invert Elevation: 7.00'
c. Orifice Flowrate, cfs: 5.12 cfs
d. Sediment Cleanout Elevation: Forebay = 11.00', Main Basin = 10.63'
e. Average Head: 1.83'
See supporting calculations pages 4 and 5 for
detailed evaluation for c,d,& e.
gEC IVED
Nov 2 9 2012
BY:
Form SW401-Dry Extended Detention Basin-Rev.3 Parts I. & II. Design Summary, Page 2 of 2

BMP element:
Potential problem
How I will remediate the roblem:
The embankment
Shrubs or trees have started
Remove shrubs or trees
to grow on the embankment.
immediately,
Grass cover is unhealthy or
Restore the health of the grass cover
eroding.
- consult a professional if necessary,
Signs of seepage on the
Consult a professional.
downstream face.
Evidence of muskrat or
Use traps to remove muskrats and
beaver activity is present.
consult a professional to remove
beavers.
An annual inspection by an
Make all needed repairs.
appropriate professional
shows that the embankment
needs repair.
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 NC Division of Water
damage have occurred at the
Quality 401 Oversight Unit at 919-
outlet.
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 basin depth reads 9.37 feet in the main pond, the sediment shall be removed.
When the basin depth reads 9.00 feet in the forebay, the sediment shall be removed.
BASIN DIAGRAM
(fill in the blanks)
Temporary Pool Elevation 13.00
Sediment Removal E 11.00 T por Pool Lem-------------olume Sediment Removal Elevation 10.63 Bottom Elevati ..25 25%-------------------------------------------
Sediment Bottom Elevation 7.00
Storage
FOREBAY MAIN POM
RECEIVED
de led-evaluabon.
OCT 2 2 2009
PROa # SGv 2OSG 5 ¢i
Form SW401-Dry Detention O&M-Rev.3 Page 3 of 4

JCI` L �Y �l1UJ _
Permit No. 0 So wwl�
(to be provided by DWQ)
fif. rt Rus a ITWS CF FcKLISr
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.
Nvap—P2
-9
Pagel Plan
Sheet No.
L-1, P-2
Exhibits F
M
M
W
SW Narrative
& Computation
V
Plans (1" - 50' or larger) of the entire site showing:
- Design at ultimate build -out,
- Off -site drainage (if applicable),
Delineated drainage basins (include Rational C coefficient per basin),
Basin dimensions,
Pretreatment system,
Maintenance access,
- Proposed drainage easement and public right of way (ROW),
- Overflow device, and
- Boundaries of drainage easement.
2. Plan details (1" = 30' or larger) for the bioretention cell showing:
- Basin dimensions
- Pretreatment system,
Maintenance access,
- Outlet structure,
Overflow device,
Flow distribution detail for basin inflow, and
Vegetation specifications.
3. Section view of the basin (1" = 20, or larger) showing:
- Side slopes, 3:1 or lower,
- Pretreatment and treatment areas, and
- Inlet and outlet structures.
6. A construction sequence that shows how the dry detention basin will be protected from sediment until the
entire drainage area is stabilized.
7. The supporting calculations.
8. A copy of the signed and notarized operation and maintenance (0&M) agreement.
9. A copy of the deed restrictions (if required).
10. A soils report that is based upon an actual field investigation, soil borings, and infiltration tests. County
soil maps are not an acceptable source of soils information.
Existing SW8 050547 information
Form SW401-Dry Extended Detention Basin-Rev.3 Part III. Required Items Checklist, Page 1 of 1

Permit No.
(to be provided by DW6y
MAA �'�WAtF9
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
HCDENR
401 CERTIFICATION APPLICATION FORM
DRY EXTENDED DETENTION BASIN SUPPLEMENT
This form must be filled out, printed and submitted.
The Required Items Checklist (Part Ill) must be printed, filled out and submitted along with all the required information.
I. PROJECT INFORMATION
Project name Wilmington International Airport Stormwater Management - Phase III
Contact person Tim Clinkscales
Phone number 910-791-6707
Date 11/8/2012
Drainage area number 1CQAAXZ70AJ
111. DESIGN INFORMATION
Site Characteristics
Drainage area
14,041,075.00
fe
Impervious area
9,751,185.00
fe
% Impervious
0.69
Design rainfall depth
1.25
in
Peak Flow Calule
RECEIVED
1-yr, 24-hr rainfall
ll depth
depth
3.83
in
Rational C, pre -development
72.00
�(unitiess)
Rational C, post -development
_
88.00
(unitless)
N O V 0 9 2012
Rainfall intensity: 1 -yr, 24-hr storm
0.76
irdhr
Pre -development 1-yr, 24-hr peak flow
75.00
le/sec
BY:
Post -development 1-yr, 24-hr peak flow
173.00 �fe/sec
Pre/Post 1-yr, 24-hr peak control
98.00
fO/sec
Storage Volume: Non -SA Waters
Minimum required volume
999,466.00
fO
Provided volume
1,274,829.05
ft'
OK
Sediment storage volume provided
241,135.00
f?
Increase to at least 25% of volume provided
Storage Volume: SA Waters
1.5" runoff volume
n/a
ft3
Pre -development 1-yr, 24-hr runoff volume
nla
f?
Post -development 1-yr, 24-hr runoff volume
n/a
le
Minimum required volume
#VALUE!
fe
Provided volume
n/a
fe
#VALUE!
Sediment storage volume provided
n/a
to
#VALUE!
Basin Design Parameters
Drawdown time
2.65 _days
OK
SHWT elevation
6.00
fmsl
Basin bottom elevation
7.00
fmsl
Raise basin bottom, Must be at least 2-ft above SHWT
Storage elevation
13.30
fmsl
Basin side slopes
4.0
• :1
OK
Top elevation
20.00
fmsl
Too deep, maximum depth of 10-feet allowed
Freeboard provided
6.70
ft
OK
Basin Bottom Dimensions
Basin length
2,125.00
ft
Basin width
450.00
ft
Length to width ratio
4.00
:1
OK
Forth SW401-Dry Extended Detention Basin-Rev.3 Parts I. & It. Design Summary, Page 1 of 2

Additional Information
Total runoff volume captured by basin
Forebay provided
Is basin in a recorded drainage easement?
Dt;a basin capture all runoff at ultimate build -out?
Is a sediment deptn indicator included?
Does the basin include a drain?
407.00 ac-in Forebay is required
y (Y or N)
y (Y or N) OK
y (Y or N) OK
y (Y or N) OK
y (Y or N) OK
Permit
(to be provided by DWfy
RECEIVED
NOV 0 9 2012
BY:
Form SW401-Dry Extended Detention Basin-Rev.3 Parts I. & II. Design Summary, Page 2 of 2

MEMORY TRANSMISSION REPORT
TIME :11-30-'12 09:41
FAX N0.1 :910-350-2004
NAME :DENR Wilmington
FILE NO.
816
DATE
: 11.30 09:39
TO
: 9 93414365
DOCUMENT PAGES
10
START TIME
11.30 09:39
END TIME
11.30 09:41
PAGES SENT
10
STATUS
OK
*** SUCCESSFUL TX NOTICE ***
Sfata a! North Carolinas
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127 C:a A1na� Y7rly Pbccansion. W31minWft� NC 2840S - (910) 70 7213 + w lequai Opporw»icy A nrwu cj Ac*jv p? p3oyer

State of North Carolina
Department of Environment and Natural Resources
Wilmington Regional Office
Beverly Eaves Perdue, Governor FAX COVER SHEET Dee Freeman, Secretary
Date: No. Pages (excl. cover):
Zv -;4�-
To: O� �D/S �o Z/ From: Jo Casmer
Co: � �i �'�Gto fy jo i / Phone: [phone]
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127 Cardinal Drive Extension, Wilmington, NC 28405 • [phone] • An Equal Opportunity Affirmative Action Employer

MEMORY TRANSMISSION REPORT
TIME :11-30-'12 09:44
FAX NO.1 :910-350-2004
NAME :DENR Wilmington
FILE NO.
817
DATE
: 11.30 09:42
TO
: F 97916760
DOCUMENT PAGES
10
START TIME
11.30 09:42
END TIME
: 11.30 09:44
PAGES SENT
10
STATUS
OK
*** SUCCESSFUL TX NOTICE ***
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Depart—..* o!maviroa®ens Mae Wataral Raroorcas
Wilmington Ramloaal OMce
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14o. Pages (excel. cover):
Plwne: [91 O) 796-7336
17
327 Cardinal Urlvo Parteesto:; Wllrsrfsl¢ton, NC 28405 • [phone] -.An 3 que1 Oppnm W /tiftirme2lve Action Srnpinyer

State of North Carolina
Department of Environment and Natural Resources
Wilmington Regional Office
Beverly Eaves Perdue, Governor FAX C3VER SEEET Dee Freeman, Secretary
Date:
To:
Co:
Fax:
No. Pages (excl. cover):
From: Jo Casmer
Phone: [phone]
Fax: [phone]
Re: Gam/ f /�!i`.� >� _/� �' iJ .4 ��"e v •;X e-- ,
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127 Cardinal Drive Extension, Wilmington, NC 28405 • [phone] • An Equal Opportunity Affirmative Action Employer

Lewis,Undla
From: Lewis, Linda
Sent: Wednesday, November 28, 2012 1:19 PM
To: 'Tim Clinkscales'
Subject: RE: Airport SW8 050547
OK, let's start at the beginning.
Per this narrative and the 2009 permit, the "first phase" of the dry basin was sized for an existing drainage area
of 150 acres containing BUA of 4,247,100 @a 1" design storm. The "second phase" of the dry basin was sized
for a proposed additional drainage area of 114 acres containing 4,220,964 of BUA @a 1.5" design storm.
Overall, the 2009 Phase I & II condition had a DA of 264 acres and a BUA of 8,468,064 sf. The storage
elevation was 13.0 and the provided volume was 1,058,112 cf.
The 2011 permit proposed to add Phase III of the basin to accommodate an additional 57.35 acres of drainage
area and a BUA of 1,479,341 sf. The new overall basin with the Phase III expansion, has a total DA of 321.35
acres (150 + 114 + 57.35) and a BUA of 9,947,406. The built -out condition of the basin (the overall condition)
has a storage elevation of 13.3 and a provided volume of 1,274,829 cf.
At this point, it is now my understanding that the existing dry basin is currently in the 2009 permitted condition,
i.e., the 2011 permit modifications to increase the storage elevation and provide additional surface area have
NOT been implemented. Therefore, the 2012 DA and BUA changes have to fit within the 2009 parameter of a
maximum volume of 1,058,112 cf.
I think I have it now. If I understand all this correctly, you have removed some DA within the existing airport that
was not required to be treated, and added DA from another location where development is more likely to occur.
This added DA is being routed to the proposed pretreatment swales.
I finally understand how the BUA was split up for the different design storms to arrive at the Ph I & 11 minimum
volume - 4,552,087 sf is at 1", and 3,968,747 is at 1.5". Based on your Oct 9, 2012 calculations, the total
minimum volume should be 1,040,576 (561032 Ph 1 + 480,101 Ph 2) for the new Ph I & II DA / BUA condition.
You got 1,045,980 from your 11/27/12 calculation, but it appears that the reported sediment storage required
volume of 194,373 is too high. The Oct. 9, 2012 calcs have a required sediment storage volume of 189,525. In
any case, the main point is that this is still below the 1,058,112 permitted in 2009 at elevation 13.0. What I still
need to do is to modify the existing 2009 supplement to reflect the new Ph I & 11 basin conditions:
DA = 12,529,107 sf
BUA = 8,520,835 sf
Percent impervious = 68%
Required minimum volume = 1,040,576 cf
Linda Lewis
NC Division of Water Quality
127 Cardinal Drive Ext.
Wilmington, NC 28405
910-796-7215
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may
be disclosed to third parties.

Lewis,Lindla
From:
Lewis,Linda
Sent:
Tuesday, November 27, 2012 4:36 PM
To:
'Tim Clinkscales'
Subject:
Airport SW8 050547
Tim -
The drainage area and BUA for the "Phase I and II" extended dry detention basin have apparently increased
since the 2009 permit condition. I had planned to just use the supplement form from the 2009 permit to reflect
the "Phase I and II" condition, but the DA and BUA on that supplement don't match what you put down on the
application in the Phase I and II column. The larger volume requirement based on the increased DA and BUA
have left a shortage in the provided volume for the 2009 permitted condition.
Your submitted calculations are geared toward the final built -out condition of 9,751,185 sf of BUA in a
14,041,075 sf DA. The 2009 permit had a Phase I and II condition DA of 11,499,840 sf and a BUA of
8,468,064 sf. This required a storage volume of 1,047,278 cf. The volume provided in the permitted basin was.
1,058,110 cf. Your 2012 proposed Phase I and II condition is now a DA of 12,529,107 sf and a BUA of
8,520,835 sf, which requires a storage volume of 1,062,740 cf. Obviously, the 1,058,110 cf isn't enough for the
new condition.
So, we either go back to the 2009 permitted DA and BUA for the Phase I and II condition or I need more
calculations and another supplement to reflect the proposed Phase I and II condition.
Linda Lewis
NC Division of Water Quality
127 Cardinal Drive Ext.
Wilmington, NC 28405
910-796-7215
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may
be disclosed to third parties.

Lewis,Unda
From: Lewis,Linda
Sent: Friday, November 09, 2012 9:39 AM
To: 'Tim Clinkscales'
Cc: 'Julie Wilsey; Russell, Janet
Subject: RE: Dry Detention Supplement SW8 050547
Tim:
The provided volume, sediment storage volume and storage elevations listed on the new dry detention
supplement you submitted are not what was previously permitted. Per the October, 2Q11 permit, the provided
volume is 1,274,829 cf, the sediment storage volume is 241,135 cf, and the temporary storage elevation is
13.3 fmsl.
It was my understanding from our express meeting, that you were not changing anything about the previously
permitted dry basin except the DA and the BUA. The calculations you provided were intended only to prove
that the drainage area and built -upon area changes had no effect on the permitted basin, and did not require
the basin to be enlarged. If that is still the case, then the only things that will change on the supplement should
be the drainage area, the built -upon area and the minimum required volume. Everything else should be the
same.
If you are now applying to change the previously permitted basin criteria (perhaps to agree with the as -built
condition?) then you will need to make that clear in the application and I will need 2 sets of updated plans (as -
built survey of the basin) and new outlet details of the dry basin showing the proposed change to the storage
elevation from 13.3 to 13.23.
Additionally, if you want to change the permitted basin criteria, then you will need to address the difference
between the 13.3 "Temporary Storage Elevation" and the 13.5 "Provided Storage Elevation" as noted in your
October 9, 2012 calculations. If the required minimum storage volume is attained at 13.23 or 13.3, but the
elevation of the outlet is placed at 13.5, then your temporary storage elevation is indeed 13.5, and not 13.23 or
13.3. Please clarify. According to the current approved dry detention plans and details, the storage elevation is
13.3, not 13.23 or 13.5.
Please advise. The 30 day express review window for this project closes today.
Linda Lewis
NC Division of Water Quality
127 Cardinal Drive Ext.
Wilmington, NC 28405
910-796-7215
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may
be disclosed to third parties.
From: Tim Ciinkscales [mailto:tclinkscalesOparamounte-eng com]
Sent: Thursday, November 08, 2012 10:15 PM
To: Lewis,Linda
Subject: RE: Airport SW8 050547
Linda,
Enclosed is the updated dry basin supplement

Let me know of anything else you need
Tim
Tim Clinkscales PE, PLS
DAR
ro rt ro¢ e rs s ro x� INC
PARAMOUNTE ENGINEERING, INC
5911 Oleander Drive, Suite 201
Wilmington, NC 28403
OFFICE: [phone]
CELL: [phone]
FAX: [phone]
From: Lewis,Linda [mailto:linda.lewis(a ncdenr.govl
Sent: Thursday, November 08, 2012 10:00 AM
To: Tim Clinkscales
Subject: Airport SW8 050547
Tim- after receiving the new DA columns split out by Phase, I noticed that the overall DA to the dry basin is
increasing and the amount of BUA is decreasing. The calculations show that the existing basin can handle this
change, but the previously approved dry detention supplement form was not updated to reflect these changes.
I can't use the old supplement because it no longer reflects the permitted condition. Please provide a new,
updated dry detention supplement showing the changes in DA and BUA. Thanks.
Linda Lewis
NC Division of Water Quality
127 Cardinal Drive Ext.
Wilmington, NC 28405
910-796-7215
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may
be disclosed to third parties.

PARAMOUNT
E N G I N E E F2 I N G, I N C.
9 9 9 1 1 OLEANDER DRIVE, SUITE 2 0 1
W I L M I N G T O N, N C 2 8 4 0 3
9 1 0- 7 9 1- 6 7 0 7( O) 9 1 0- 7 9 1- 6 7 6 0 ( F)
LETTER OF TRANSMITTAL
To:
NCDENR-Land Quality Section
Date
1 11/2/12
127 Cardinal Drive Extension
Wilmington, NC 28405
Re:
Wilmington International Airport
Stormwater MOD & Pre -Treatment
Attn:
Project No. I
12212.PE
e are sen&nd
® Originals
® Prints
❑ Shop Drawings
❑ Calculations
❑ Correspondence
® Plans
❑ Specifications
® Other as listed below
he followin items
Quantity
Date
Dwg. No.
Description
1
Response Letter
1
Updated SW401 Forms
1
Updated SWU-101 Attachment
1
Additional Calculations
Issue Status. -I ® For Approval ❑ As Requested ❑ Construction ❑ Bid
❑ For Your Use ❑ For Review and Comment ❑ Approved as Noted ❑ See Remarks
ction Taken: ❑ No Exceptions Taken ❑ Make Corrections Noted ❑ Amend & Resubmit
❑ Rejected - See Remarks ❑ Approved as Submitted ❑ Other
Tim Clinkscales
)r rI

PARAMOUNTE
E N G I N E E R 1 N G
October 17, 2012
Linda Lewis
NC Division of Water Quality
127 Cardinal Drive Ext.
Wilmington, NC 28405
RE: Request for Additional Information — Express Review
Stormwater Project No. SWS 050547
Wilmington International Airport
New Hanover County
Dear Ms. Lewis:
N C.
NOV 0 2 2012
BY:
On behalf of Wilmington International Airport, we are submitting a response to your comments
received on October 170, 2012. The please find your comments listed below with our response
provided in bold.
The "for credit" grassed swales must meet two separate velocity criteria: 1) provide a non -
erosive velocity for the peak flow of the 10 year stone; and, 2) provide a maximum velocity of
1 fps for the 10 year 24 hour stone. The calculations appear to provide only the 10 year peak
flow instead of the 10 year 24 hour storm to demonstrate compliance with the 1 fps velocity
limit. Essentially, you need to provide two velocity calculations, one based on the 10 year
peak flow (to demonstrate nonerosive flow for the chosen swale lining and slope) and one
based on the less intense 10 year 24 hour storm (to demonstrate that the velocity is no more
than 1 fps.)
We have performed the velocity calculation within the swales by first calculating
the flow rate (Q) at different storm events. Flow rate (Q) was achieved by using
the Rational Method to determine storm water runoff (Q=CIA). This method is
able to give the designer flow rates at different design storms (1 yr., 10 yr. , 25
yr., and so on). The flow rates per design storm are achieved through the
corresponding intensity rainfall rate ("I"). "I" is achieved through IDF curves
(Intensity Duration Factor) where the intensity varies as the time of
concentration ("Tc") varies. Therefore, the Rational Method gives a Peak Flow
Rate for the Storm Intensity implemented. Now the language 1110 year 24 hour
storm" reflects a different method than the Rational to estimate Stormwater
Runoff called the SCS Method (NRCS Method). The SCS Method uses Rainfall
Depth (P) instead of Rainfall Intensity (1) in the input to achieve volume and
peak flow rate. The SCS Method calculates a peak flow rate along a bell shaped
curve (curves differ by Types and Shape Factors); this method is not a simple
calculation. We did not use the SCS Method to calculate Flow rate (Q) but
rather the Rational Method. In short, there is only one velocity to be calculated
(peak velocity), the storm duration ("10 yr. 24 hour") is rhetoric differentiating
between different methods. Please find the Peak Velocity calculation submitted
5 9 1 1 ❑ L E A N ❑ E R ❑ R I V E, S T E. 2 ❑ 1, WILMIN G T❑ N. N ❑ 2 E 4 ❑ 3
P H: 1 9 1 0 1 7 9 1 - 6 7 ❑ 7 F A X: ( 9 1 ❑ ) 7 9 1 - 6 7 6 ❑

as meeting the requirement to provide peak velocity calculations for the 10 year
storm event (10 year 24 hour storm event language would be applicable if we
used the SCS Method).
Using the rational method for the peak intensity for the 10-yr — 24 hour storm
with an intensity of 0.301 in/hr per NOAA website
For Swale #1, a C-value of 0.67 and area of 115.52, the Q(peak) = 23.3 cfs
For Swale #2, a C-value of 0.75 and area of 116.98, the Q(peak) = 26.4 cfs
See calculations for Velocity calculations
2. Please explain in detail how you derived the values for time of concentration used in the swale
calculations. Please document any assumptions regarding the height of the most remote point
in the watershed, the length of the flow path and how much of that flow path will be piped or
channelized. These assumptions should necessarily be based on the "worst -case" built -out
scenario.
In order to give the "worst -case" built -out scenario would assume that the entire
system is built via pipe networks. Therefore it is required for the Designer to
estimate length of the storm drain network and the velocity within the pipes in
order to arrive at a time to arrive downstream from the most remote location.
Please see the calculation below which was performed in -line to the hydraulic
analysis performed by Talbert & Bright while designing the downstream
Detention Basin. The Tc used by Talbert & Bright for the built -out basin was
180 minutes, which is greater than either scenarios employed by Paramounte;
therefore our calculation will give NCDENR a higher velocity due to a shorter
Tc.
Tc. Swale 1 (Pipe Flow)
Hydraulic Length=
4800 if
Pipe Slope=
0.002 ft/ft
n =
0.013 (rcp)
Diameter--
4 ft (avg. size Win basin)
Velocity--
0.97 fps
T=
82 min.
Tc. Swale 2 (Pipe Flow)
Hydraulic Length=
7300 If
Pipe Slope=
0.002 ft/ft
n =
0.013 (rcp)
Diameter--
5 ft (avg. size Win basin)
Velocity=
1.13 fps
T=
108 min.
2 2012
Nov o
13Y:
The velocity in the pipe is achieved using the empirical Manning's Equation
which employs the pipe diameter, pipe slope, and Manning's "n". Note that we
5 9 1 1 ❑ L E A N D E R D R! V E, 5 T E. 2 ❑ 1. W 1 L M I N G T❑ N. N C 2 2 4 ❑ 3
P H: ( 9 1 0) 7 9 1 - 6 7❑ 7 F A X: ( 9 1 0) 7 9 1 - G 7 G❑

could add overland -flow to the pipe system to the Tc but if the velocity works for
the lesser Tc then it will work as more Time is added on.
3. Please provide documentation of the 0.042 Mannings "n" value used in the swale calculations.
A value of 0.042 seems high when compared to the tables published in V.T. Chow's Open
Channel Hydraulics, 1959, McGraw-Hill, and to the procedures for determining channel
roughness coefficients described in the Erosion and Sediment Control Planning and Design
Manual (ESCPDM). The V.T Chow tables provide Manning's n-values for a wide range of
channel types. The n-value for an excavated, straight, uniform, earthen channel with short
grass and a few weeds has a range of 0.022 — 0.033. The Division uses a "normal" value of
.027 which is supported by the procedures described in the ESCPDM. Based on the Division's
value, the resulting velocity in both swales is >1 fps, but is less than the maximum permissible
velocity of 5 fps for a grass -lined swale. However, this velocity calculation is not based on the
10 year 24 hour storm, which will have a smaller intensity which will in all likelihood, reduce
the velocity below 1 fps.
In effort to satisfy NCDENR requirements and also New Hanover County
Stormwater Requirements to be submitted and approved in the future, we used
chart (Figure 60-4) within Section 60 — Open Channel Design Procedures with -in
the New Hanover County Storm Water Design Manual (See attached). As you
can see, we used "Curve D" to be in line with the O&M agreement. With a
product of Velocity and Hydraulic Radius, we arrived at a Manning's n factor of
0.042 for vegetative retardance.
4. Bermuda is specified as the permanent grass type on the grassed swale supplement forms
submitted with the application, however, centipede is specified on the plans. Centipede takes
several years to establish. What sort of temporary liner will be used in the meantime to prevent
erosion? If the swales will be seeded and not sodded, please provide additional swale
calculations using the peak flow from a 10 year storm and a Mannings "n" value for an
excavated, straight, uniform, earthen channel, recently completed (0.016 — 0.02) to determine
if a temporary liner is needed to prevent erosion.
• The grass on the supplement has been updated to centipede type grass, since not
a choice, it is marked out on the supplement form. In addition, calculations have
been provided that velocity for the earthen channel are below the threshold for
lining being required
5. The application erroneously indicates that the last permit issued for this project is dated
October 28, 2009. The current in -effect permit was issued on October 26, 2011. If the
information you have provided in the most recent modified application is based on making
changes to the information in the 2009 permit, please adjust accordingly in light of the 2011
permit.
The areas in the permit application were based on the October 2Q10h ► nELUI
and are correct
S 9 1 1 ❑ L E A N D E R D R 1 V E, T E. 2 ❑ 1, W 1 L M 1 N G T ❑ N, N C 2 8 4 ❑ 3
P H : f 9 1 0 1 7 9 1 - 6 7 n 7 F A X: [9 1 171 1 79 1 - 6 7 6 ❑

6. Due to the design storm differences, and to be consistent with how the 2011 permit application
was completed, and to cut down on the confusion, please list the proposed drainage areas and
built -upon areas for Phases 1, 11 and III in separate columns on the application.
• The SWU-101 attachment has been updated to reflect such
7. Runways, taxiways, and any other areas that provide for overland stormwater flow, promote
infiltration and treatment of stormwater into grassed buffers, shoulders, and grass swales are
deemed permitted pursuant to the State's post -construction stormwater requirements. Please
request DWQ concurrence that those areas of the airport that are to be "deemed permitted"
meet the Session Law requirements. Although the law did not mandate that an airport submit
anything or document compliance with the Session Law, it is my understanding that not doing
so could subject the Airport to civil penalties (NOV) and/or leave them open to third party
The burden of proof is on the airport, so having a concurrence letter from the state would go a
long way to making a case that the airport is indeed in compliance with the Session Law. In
order to provide this concurrence, please delineate and identify the areas which are to be
"deemed permitted" under the Airport Session Law and demonstrate the required overland
sheet flow by providing a grading plan. Otherwise, an inspection of that area will be
conducted to determine compliance with the Session Law requirements prior to approving the
requested permit modification.
While SB 229 was passed in August 2012, the actual guidance for storm water on
airports and Best Management Practices (Chapter 13) is out for public comment
until December 2, 2012. Overland flow (Section 13.7) is a component of the
manual, and we believe it is too early to be requesting concurrence for airport
areas to be "deemed permitted" under the new law. Since this permit
modification is for a landside project, and we are using existing NCDENR BMPs,
we defer the "deemed permitted" issue until the Airport BMP manual has
completed the review period and any subsequent revisions. (comment from
Airport Authority).
Feel free to contact me directly by phone if you have any further questions or concerns.
Sincerely,
Tim Clinkscales, PE, PLS
Paramounte Engineering, Inc.
NOV 0 2 2012
5 9 1 1 ❑ L E A ,J D E R D R I V E T E, 2 ❑ 1, W I L M I N G T ❑ N N C 2 H 4 ❑ 3
P H: ! 9 1 ❑) 7 9 1 - 6 ❑ 7 F A X: (9 1 U) 7 9 1 - 6 7 6❑

PRE-TREATMENT SWALE DESIGN/MODIFICATION
PER SL 2012-200
NEW HANOVER COUNTY, NORTH CAROLINA
STORMWATER NARRATIVE
Prepared for:
Wilmington International Airport
1740 Airport Blvd.
Wilmington, NC 28405
Prepared by:
-- - -- - - _ Pao 's 4
PARAMOUNTE rNOV
EC0 2 2012EI VED
E N C I N E E R I N G. 1 N C
5911 Oleander Drive, Suite 201
Wilmington, NC 28403 BY:
Project #12212.PE
s i
October 2012 S r ;
LU
�jy �NG I N��•'•5G4
OCT 0 9 2012

PRE-TREATMENT SWALE DESIGN
NEW HANOVER COUNTY, NORTH CAROLINA
Project #12212.PE
Table of Contents
Design Narrative
Soils Map
USGS Map
Stormwater Calculations
Dry Basin Calculations
OCT 0 9 2012

PRE-TREATMENT SWALE DESIGN
NEW HANOVER COUNTY, NORTH CAROLINA
Project #12212.PE
DESIGN NARRATIVE
The Wilmington International Airport proposes to permit a Pre -Treatment device to serve a portion of
the existing Dry Basin drainage area (SW8 050547). It is proposed to utilize two grassed swales per DWQ
Pre -Treatment requirements (requirements per DWQ Ch. 14 — Grassed Swale downloaded 08/17/12) for a
Pollutant Removal credit of 35% TSS.
The proposed Pre -Treatment Swales will drain to a currently permitted Dry Basin (SW8 050547) which in
turn drains to an unnamed tributary of Smith Creek (C; Sw) [18-74-631 within the Cape Fear River Basin.
According to the NRCS Soil Survey of New Hanover County the majority of the soil across the drainage
area consists of Leon sand (Le) and Seagate fine sand (Se). The drainage area currently consists of a
majority of grassed area and a small amount of existing impervious.
In addition to the permitting of pre-treatment swales, the existing permit is being modified based on SL
2012-200 that was signed in August for airport facilities. The modification will remove areas that are
considered airside activities to the Wilmington International Airport and do not naturally drain to the
constructed basin. a permit modification depicts the area the currently constructed dry basin can
handle before the Phase III expansion is required. The area was determined as shown on the design
sheets and calculations that follow. The limiting factor in determining the area the basin can hold before
the Phase III construction is required is the volume of storage required. PEI has determined the amount
of drainage area with corresponding impervious area that equals the previously permitted volume of
storage for the combination of the Phase I and II permit modifications. For this volume, areas that were
permitted in the Phase III expansion can be developed before the threshold of storage volume is reached.
Because of this, the design storm of 1.5" was used for the Phase III areas. For this case, the 11.4 acres of
wetlands in the Phase II section were calculated to 0% impervious unlike the 85% in the past permits.
Also the area of the pretreatment swales were calculated as 0% impervious unlike the 65% in the past
permits
PEI also checked the total volume of storage required for the entire basin including the Phase III
expansion and these calculations are shown as well. To match the storage volumes including the Phase
III expansion, a storage volume was calculated using an arbitrary drainage area and impervious area, this
is depicted in the stormwater table as "future impervious to meet original design". This was calculated
to match as close as possible to approved permit on October 26, 2011.
OCT u.:9 2012

SOILS MAP
OCT 0.9 ZOIZ

1O 77' 55' 29'
�W �z
I ' g
:n.
g
5T
a
0
91 x
g`
77' 54' 4V'
_ . A".
y �
OCT 0.9 Z01Z
I
77' 55' 29'
77' 54' 49"

USGS MAP
OCT u 9 2012

STORMWATER CALCULATIONS
OUT 0,9 2012

Project Name: Bus. Park PH. 3 Stormwater ` AR1"'3 MO V 1 �I T
Client: ILM E
Project Number: 12212.PE a, N E
Prepared By: TGC
Date: 10/5/12
Pre -Treatment Area #1 - Swale Calculations
Drainage Area =
115.52 Ac.
Impervious Area =
75.08 Ac.
% Impervious =
65.0%
CGRASS =
0.15
CIMPERV. =
0.95
CWEIGHTED =
0.67
Tc =
82 min.
I10YR. =
2.38 in/hr
Q10VR. =
184 cfs
Swale Parameters
B (Base Width) =
22 ft
m (Side Slope) =
5 m:1
S (Long. Slope) =
0.02 %
D (Total Depth) =
13 ft
d (Depth @ Peak) =
4.26 ft
VAcruAL =
1.00 fps
Swale Requirements
Non -erosive Vel. @ 10 yr. =
Less than 1 fps
Free Board (6" req.) =
Approx. 6' (72") provided
Swale Length =
150'
Side Slopes =
5:1
OCT 0 .9 2012

Channel Report
Hydraflow Express Extension forAutoCAD® Civil 3D®2009 byAutodesk, Inc.
PRE-TREATMENT SWALE-1
Trapezoidal
Bottom Width (ft)
= 22.00
Side Slopes (z:1)
= 5.00, 5.00
Total Depth (ft)
= 13.00
Invert Elev (ft)
= 11.50
Slope (%)
= 0.02
N-Value
= 0.042
Calculations
Compute by: Known Q
Known Q (cfs) = 184.00
Elev (ft)
25.00
23.00
21.00
19.00
17.00
15.00
13.00
11.00
9.00
0 20 40 60 80
Section
Friday, Oct 5 2012
Highlighted
Depth (ft)
= 4.26
Q (cfs)
= 184.00
Area (sqft)
= 184.46
Velocity (ft/s)
= 1.00
Wetted Perim (ft)
= 65.44
Crit Depth, Yc (ft)
= 1.18
Top Width (ft)
= 64.60
EGL (ft)
= 4.28
Depth (f
13.50
11.50
4 e
7.50
5.50
3.50
1.50
-0.50
-2.50
100 120 140 160 180 200
UUT 0 9 2012
RPar:h (ft)

Project Name: Bus. Park PH. I Stormwater
Client: ILM pARAo►uNTE
Project Number: 12212.PE
Prepared By: TGC
Date: 10/5/12
Pre -Treatment Area #2 - Swale Calculations
Drainage Area =
116.98 Ac.
Impervious Area =
88.00 Ac.
% Impervious =
75.2%
CGRAss =
0.15
CIMPERV. =
0.95
CWEIGHTED =
0.75
Tc =
108 min.
I10YR. =
1.96 in/hr
Q10YR. =
172 cfs
Swale Parameters
B (Base Width) =
22 ft
m (Side Slope) =
5 m:1
S (Long. Slope) =
0.02 %
D (Total Depth) =
13 ft
d (Depth @ Peak) =
4.12 ft
VAcruAL =
0.98 fps
Swale Requirements
Non -erosive Vel. @ 10 yr. =
Less than 1 fps
Free Board (6" req.) =
Approx. 6' (72") provided
Swale Length =
150'
Side Slopes =
5:1
OCT 0 9 2012

Channel Report
Hydraflow Express Extension forAutoCAD® Civil 3D® 2009 byAutodesk, Inc.
PRE-TREATMENT SWALE-2
Trapezoidal
Bottom Width (ft)
= 22.00
Side Slopes (z:1)
= 5.00, 5.00
Total Depth (ft)
= 13.00
Invert Elev (ft)
= 11.50
Slope (%)
= 0.02
N-Value
= 0.042
Calculations
Compute by: Known Q
Known Q (cfs) = 172.00
Elev (ft)
25.00
23.00
21.00
19.00
17.00
15.00
13.00
11.00
9.00
0 20 40 60 80
Section
Friday, Oct 5 2012
Highlighted
Depth (ft)
= 4.12
Q (cfs)
= 172.00
Area (sqft)
= 175.51
Velocity (ft/s)
= 0.98
Wetted Perim (ft)
= 64.02
Crit Depth, Yc (ft)
= 1.14
Top Width (ft)
= 63.20
EGL (ft)
= 4.13
Depth (f
13.50
11.50
9.50
7.50
5.50
3.50
1.50
-0.50
-2.50
100 120 140 160 180 200
OCT U 9 2012
RPac:h (ft) 1PV

Channel Report
Hydraflow Express Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc.
Thursday, Nov 1 2012
PRE-TREATMENT SWALE-1
DURING CONSTRUCTION
Trapezeldal
Highlighted
Bottom Width (ft)
= 22.00
Depth (ft)
= 2.62
Side Slopes (z:1)
= 5.00, 5.00
Q (cfs)
= 184.00
Total Depth (ft)
= 13.00
Area (sqft)
= 91.96
Invert Elev (ft)
= 11.50
Velocity (ft/s)
= 2.00
Slope (%)
= 0.02
Wetted Perim (ft)
= 48.72
N-Value
= 0.016
Crit Depth, Yc (ft)
= 1.18
Top Width (ft)
= 48.20
Calculations
EGL (ft)
= 2.68
Compute by:
Known Q
Known Q (cfs)
= 184.00
Elev (ft)
25.00
23.00
21.00
19.00
17.00
15.00
13.00
11.00
9.00
0
j1EC,F-1Vrt
NOV 02292
Section Depth (ft)
13.50
11.50
9.50
7.50
5.50
3.50
1.50
-0.50
-2.50
20 40 60 80 100 120 140 160 180 200
Reach (ft)

Channel Report
Hydraflow Express Extension for AutoCAD® Civil 3138 2009 by Autodesk, Inc. Thursday, Nov 12012
PRE-TREATMENT SWALE-2 - DURING CONSTRUCTION
Trapezoidal
Highlighted
Bottom Width (ft)
= 22.00
Depth (ft)
= 2.53
Side Slopes (z:1)
= 5.00, 5.00
Q (cfs)
= 172.00
Total Depth (ft)
= 13.00
Area (sqft)
= 87.66
Invert Elev (ft)
= 11.50
Velocity (ft/s)
= 1.96
Slope (%)
= 0.02
Wetted Perim (ft)
= 47.80
N-Value
= 0.016
Crit Depth, Yc (ft)
= 1.14
Top Width (ft)
= 47.30
Calculations
EGL (ft)
= 2.59
Compute by:
Known Q
Known Q (cfs)
= 172.00
RECENED
NOV 0 2 2012
BY:
Elev (ft) Section Depth (ft)
25.00 13.50
23.00 11.50
21.00 9.50
19.00 7.50
17.00 5.50
15.00 ri 3.50
I
13.00 1.50
11.00 -0.50
9.00 -2.50
0 20 40 60 80 100 120 140 160 180 200
Reach (ft)

Channel Report
Hydraflow Express Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc.
Thursday, Nov 1 2012
PRE-TREATMENT SWALE-1
- RATIONAL METHOD PEAK FLOW
Trapezoidal
Highlighted
Bottom Width (ft)
= 22.00
Depth (ft)
= 1.45
Side Slopes (z:1)
= 5.00, 5.00
Q (cfs)
= 23.30
Total Depth (ft)
= 13.00
Area (sqft)
= 42.41
Invert Elev (ft)
= 11.50
Velocity (ft/s)
= 0.55
Slope (%)
= 0.02
Wetted Perim (ft)
= 36.79
N-Value
= 0.042
Crit Depth, Yc (ft)
= 0.32
Top Width (ft)
= 36.50
Calculations
EGL (ft)
= 1.45
Compute by:
Known Q
Known Q (cfs)
= 23.30
Elev (ft)
25.00
23.00
21.00
19.00
17.00
15.00
13.00
11.00
9.00
0 20 40 60
RECEIVED
NOV 0 2 2D12
BY:
Section
Depth (ft)
13.50
11.50
9.50
FAM11
1=11
3.50
1.50
-0.50
-2.50
80 100 120 140 160 180 200
Reach (ft)

Channel Report
Hydraflow Express Extension for AutoCAD@ Civil 3D@ 2009 by Autodesk, Inc.
Thursday, Nov 12012
PRE-TREATMENT SWALE-2 - RATIONAL METHOD
Trapezoidal
Highlighted
Bottom Width (ft)
= 22.00
Depth (ft)
= 1.56
Side Slopes (z:1)
= 5.00,5.00
Q (cfs)
= 26.40
Total Depth (ft)
= 13.00
Area (sqft)
= 46.49
Invert Elev (ft)
= 11.50
Velocity (ft1s)
= 0.57
Slope (%)
= 0.02
Wetted Perim (ft)
= 37.91
N-Value
= 0.042
Crit Depth, Yc (ft)
= 0.35
Top Width (ft)
= 37.60
Calculations
EGL (ft)
= 1.57
Compute by:
Known Q
Known Q (cfs)
= 26.40
NOV 0 2 2012
Elev (ft) Section Depth (ft)
25.00 - 13.50
23.00
11.50
21.00 -
9.50
19.00 - 7.50
17.00 - 5.50
15.00 - 3.50
13.00 - T- 1.50
11.00 - -0.50
9.00 - -250
0 20 40 60 80 100 120 140 160 180 200
Reach (ft)

NEwffim R CoUNTPSTORM WATER DESIGN MANUAL
SECU02V 60 - OPEN CHANNEL DESIGNPROCEDURES
Steps for determining channel design for using a vegetative lining proceeds as follows:
60.2.1
60.2.2
60.2.3
60.2.4
60.2.5
With the known flow rate, Q, and channel slope, s, select channel geometry
type and lining type.
Determine permissible velocity from Table 60-1.
Estimate channel size by dividing Q by the permissible velocity. Then
estimate channel width, depth and side slope to fit site conditions.
Compute the hydraulic radius of the trial channel configuration.
Determine Manning's n using vegetative retardance class from Figure 60-4
and the graph below using the permissible velocity and hydraulic radius. It is
recommended to use at least one retardance class higher than the one
determined from the graph.
Y=_ =a-
P F6
V = 1,00
Nov 0�2 2012
60.2.6 Calculate velocity and flow using Manning's equation. Compare results with
Permissible velocity and required capacity.
60.2.7 Repeat the above. steps as necessary adjusting channel geometry to obtain
required capacity within velocity limitations.
60.2.7.1 The nomograph on Figure 60-2 provides for the solution of
equation for a trapezoidal channel with side slopes from 1 to 6 horizontal to
vertical. An example is shown in the lower right comer of the nomograph.
60.2.7.2 If the channel velocity exceeds 2 fps, a temporary lining may be required to
stabilize the channel prior to the vegetation establishing. The procedure for
designing temporary linings is the same as shown for riprap lined channels.
ADOPTED SEPTEMBER S, 2000
PAGE 60-5

NEWHANOYER COUN7YSTORM WATER DESIGNMANUAL
SEC77ON 60 - OPEN CHANNEL DESIGNPROCEDURES
Steps for determining channel design for using a vegetative lining proceeds as follows:
60.2.1 With the known flow rate, Q, and channel slope, s, select channel geometry
type and lining type.
60.2.2 Determine permissible velocity from Table 60-1.
60.2.3 Estimate channel size by dividing Q by the permissible velocity. Then
estimate channel width, depth and side slope to fit site conditions.
60.2.4 Compute the hydraulic radius of the trial channel configuration.
60.2.5 Determine Manning's n using vegetative retardance class from Figure 60-4
and the graph below using the permissible velocity and hydraulic radius. It is
recommended to use at least one retardance class higher than the one
determined from the graph.
a..,, = 2:-74
V=0.9S PPs
v�--977
RECEIVED
NOV 0 � 2012
BY:�_
60.2.6 Calculate velocity and flow. using Manning's equation. Compare results with
Permissible velocity and required capacity,
60.2.7 Repeat the above -steps as necessary adjusting channel geometry to obtain
required capacitywithm velocity limitations.
60.2.7.1 The nomograph on Figure 60-2 provides for the solution of Manning's
equation for a trapezoidal channel with side slopes from 1 to 6 horizontal to 1
vertical. An example is shown in the lower right corner of the nomograph,
60.2.7.2 If the channel velocity exceeds 2 fps, a temporary lining may be required to
stabilize the channel prior to the vegetation establishing. The procedure for
designing temporary linings is the same as shown for riprap lined channels.
ADOPTED SEPTEMBER 5, 2000 -
PAGE 60-5

DRY BASIN CALCULATIONS
OCT 0 9 2012

Project Name: PH.III Detention Expansion
Client: ILM
Project Number: 11181.PE
Prepared By: TGC
Date: October 2011 approval
State Stormwater Information (Mod. SW8050547)
Phase I (Per SWSOS0547 Mod.)
Drainage Area =
6,534,000 sf
Impervious =
4,247,100 sf
% Impervious =
65.00 %
Design Rainfall Depth =
1.00 in
Volume Req. =
345,758 cf
Min. Req. Sed. Storage =
20 %
Req. Sed. Storage Volume =
69,152 cf
Min. Req. Volume w/ Sed. Storage =
414,910 cf
Phase II (Per SW8050547 Mod.)
Drainage Area =
4,965,840 sf
Impervious =
4,220,964 sf
% Impervious =
85.00 %
Design Rainfall Depth =
1.50 in
Volume Req. =
505,895 cf
Min. Req. Sed. Storage =
25 %
Req. Sed. Storage Volume
126,474 cf
Min. Req. Volume w/ Sed. Storage
632,369 cf
Phase III (Proposed Phase for Permit Mod.)
Drainage Area =
2,498,325 sf
Impervious =
1,479,341 sf
% Impervious =
59.21 %
Design Rainfall Depth =
1.50 in
Runoff Coefficient, Rv =
0.583
Volume Req. =
182,040 cf
Min. Req. Sed. Storage =
25 %
Req. Sed. Storage Volume =
45,510 cf
Min. Req. Volume w/ Sed. Storage =
227,550 cf
Total Basin Information
Drainage Area =
Impervious =
% Impervious =
Volume Req. =
Req. Sed. Storage Volume =
El. @ Sed. Storage Volume =
Min. Req. Volume w/ Sed. Storage =
Design Rainfall Depth (Weighted) _
Req. Forebay Volume =
Provided Forebay Volume =
Temporary Storage Elevation =
Provided Storage Elevation =
Provided Storage Volume =
Drawdown Time =
'PARAMOUNTE
13,998,165 sf
9,947,405 sf
71.06 %
1,033,693 cf
241,135 cf
10.96 el.
1,274,829 cf
1.27 in
254,966 cf
20.67 %
13.30 el.
13.50 el. �� No
1,397,405 cf
2.65 days
nW- ccerge-t-
OCT
0,911 201Z
1P'Y: _

Project Name: PH.III Detention Expansion -Airport Exemption SL 2012-200
Client: ILM
Project Number: 11181.PE
Prepared By: TGC- ............... ...
Date: 1019/12 D � RA MOO N T E
E N G N IN IN
State Stormwater Information (Mod. SW8050547)
Phase I (Per SW8050547 Mod.)
Drainage Area =
8,292,894 sf
Impervious =
5,342,129 sf
% Impervious =
64.42 %
Design Rainfall Depth =
Volume Req. =
I cf
Min. Req. Sed. Storage =
1
Req. Sed. Storage Volume =
93,
Min. Req. Volume w/ Sed. Storage
I cf
Phase II (Per SW8050547 Mod.)
Drainage Area =
4,236,212 sf
Impervious =
3,178,705 sf
% Impervious =
75 %
Design Rainfall Depth =
1.50 in
Volume Req. =
384,081 cf
Min. Req. Sed. Storage =
25 %
Req. Sed. Storage Volume =
96,020 cf
Min. Req. Volume w/ Sed. Storage =
480,101 cf
Phase III (Proposed Phase for Permit Mod.)
Drainage Area =
1,511,968 sf
Impervious =
1,230,350 sf
% Impervious =
81.37 %
Design Rainfall Depth =
1.50 in
Runoff Coefficient, Rv
0.782
Volume Req. =
151,432 cf
Min. Req. Sed. Storage =
25 %
Req. Sed. Storage Volume =
37,858 cf
Min. Req. Volume w/ Sed. Storage =
189,290 cf
Total Basin Information
Drainage Area =
14,041,074 sf
Impervious =
9,751,184 sf
Impervious =
69.45 %
Volume Req. =
1,003,039 cf
Req. Sed. Storage Volume =
227,383 cf
El. @ Sed. Storage Volume =
10.88 el.
Min. Req. Volume w/ Sed. Storage =
1,230,423 cf
Design Rainfall Depth (Weighted) =
1.30 in
Req. Forebay Volume =
254,966 cf
Provided Forebay Volume =
20.67 %
Temporary Storage Elevation =
13.30 el.
Provided Storage Elevation =
13.50 el.
Provided Storage Volume =
1,397,405 cf
Drawdown 'rime =
2.65 days
S(of vas,
­kl ggo t a l
4>>.33
10 1
401
OCT 0 1 2012

- -.. _....--- ............... .......................... ................. .....
PARAMOUNTE
Phase I (Per SWS050547 Mod.) Oct 2012 Update
Addition from Phase III
Pre -Treatment Swale Area
Drainage Area =
7,003,210 sf
1,215,450
74,234
Impervious =
4,552,087 sf
790,043
0
% Impervious =
65.00 %
65.00
0.00
Design Rainfall Depth =
1.00 in
1.50
1.50
Runoff Coefficient, Rv =
0.635
0.63
0.050
Volume Req. _
7 cf
96,476
464
Phase II (Per SW8050547 Mod.)
Drainage Area =
4,236,212 sf
Impervious =
3,178,705 sf
% Impervious =
75.04
Design Rainfall Depth =
1.50 in
Runoff Coefficient, Rv
0.725
Volume Req. =
384,081 cf
Phase III (Proposed Phase for Permit Mod.)
Future to meet original design
Drainage Area =
1,511,968 sf
570820
sf Equivalent Area
Impervious =
899,275 sf
331075
sf
% Impervious =
59.48 %
58.00
%
Design Rainfall Depth =
1.50 in
1.50
in
Runoff Coefficient, Rv =
0.585
0.572
Volume Req. =
110,618 cf
40,814
cf
OCT 0 9 2012

State Stormwater Information (Mod. SW8050547 October 2011)
Phase 1 and II (Per SW8050547 Mod.)
Drainage Area =
11499840 sf
Impervious =
8468064 sf
% Impervious =
73.64
Volume Req. =
851653 cf
Req. Sed. Storage Volume
195626 cf
Min. Req. Volume w/ Sed. St(
1047279 of
Phase III (Proposed Phase for Permit Mod.)
Drainage Area = 2498325 sf
impervious = 1479341 sf
% Impervious = 59.21 %
Volume Req. = 182040 cf
Min. Req. Volume w/ Sed. 227550 cf
State Stormwater Information (Mod. SW80SO547 November 2012 Update)
Total Phase I and II as in Supplement
Drainage Area = 12,529,106
Impervious = 8,520,834
% Impervious = 68.01
Volume Req. = 851,601 ✓ey,��C
Req. Sed. Storage Volume 194373
Min. Req. Volume w/ Sed. Storage = 1,045,98
Phase III as in Supplement
Drainage Area = 1,511,051
Impervious _ 1,230,350
% Impervious = 81.42
Volume Req. = 147,858
Min. Req. Volume w/ Sed. Storage 184,823
Total Basin Information
Total Basin Information
Drainage Area =
13998165 of
Drainage Area =
Impervious =
% Impervious =
9947405 sf
Impervious =
Volume Req. =
71.06 %
1033693 of
% Impervious =
Volume Req.. =
Req. Sed, Storage Volume =
El. (81 Sed. Storage Volume =
241135 cf
Req. Sed. Storage Volume =
Min. Req. Volume w/ Sed. St(
10.96 el.
1274820 of
El. @ Sed. Storage Volume =
Min. Req. Volume w/ Sed. Storage
Design Rainfall Depth (Weigh
Req. Forebay Volume -
1.27 in
Design Rainfall Depth (Weighted)
Provided Forebay Volume =
254966 cf
20.67 %
Req Forebay Volume =
Temporary Storage Elevation
13.3 el.
Provided Forebay Volume =
Temporary Storage Elevation =
Provided Storage Elevation =
13.5 el.
Provided Storage Elevation =
Provided Storage Volume =
1397405 cf
Provided Storage Volume =
Drawdown Time =
2.65 days
Drawdown Time =
14,040,157
9,751,184
69.45
999465.92
231337.153
10.91
1230803
1.J_5
246,161
283,473
13.23
13.5
1,397,405
2.65
P owl I0'q-I Z
-f If�gsZ2
/04

Lewis,Linda
From: Tim Clinkscales [[e-mail]]
Sent: Thursday, October 18, 2012 2:54 PM
To: Lewis,Linda; Julie Wilsey
Cc: Russell, Janet
Subject: RE: Additional Information / SW8 050547
Attachments: MANNINGS CALC-ILM.pdf
Linda,
For the comments you have provided for items 1-3, we would like to work through these issues before any formal
resubmittals because these are items that need to clarified in such a manner. The other reason for this is to avoid
resubmittal fees that may be required as we discuss these calculations. I know this may not be common practice in the
express program but we believe this may be the best way to communicate for these items for both parties on this
project. We would appreciate such on this project
We are enclosing our response to these three comments and related information
Thanks for your time and have a good day
1. The "for credit" grassed swales must meet two separate velocity criteria: 1) provide a non -erosive velocity for
the peak flow of the 10 year storm; and, 2) provide a maximum velocity of 1 fps for the 10 year 24 hour storm.
The calculations appear to provide only the 10 year peak flow instead of the 10 year 24 hour storm to
demonstrate compliance with the 1 fps velocity limit. Essentially, you need to provide two velocity calculations,
one based on the 10 year peak flow (to demonstrate nonerosive flow for the chosen swale lining and slope) and
one based on the less intense 10 year 24 hour storm (to demonstrate that the velocity is no more than 1 fps.)
We have performed the velocity calculation within the swales by first calculating the flow rate (Q) at
different storm events. Flow rate (Q) was achieved by using the Rational Method to determine storm
water runoff (Q=CIA). This method is able to give the designer flow rates at different design storms (1
yr., 10 yr., 25 yr., and so on). The flow rates per design storm are achieved through the corresponding
intensity rainfall rate ("I"). "I" is achieved through IDF curves (Intensity Duration Factor) where the
intensity varies as the time of concentration ("Tc") varies. Therefore, the Rational Method gives a
Peak Flow Rate for the Storm Intensity implemented. Now the language "10 year 24 hour storm"
reflects a different method than the Rational to estimate Stormwater Runoff called the SCS Method
(NRCS Method). The SCS Method uses Rainfall Depth (P) instead of Rainfall Intensity (1) in the input to
achieve volume and peak flow rate. The SCS Method calculates a peak flow rate along a bell shaped
curve (curves differ by Types and Shape Factors); this method is not a simple calculation. We did not
use the SCS Method to calculate Flow rate (Q) but rather the Rational Method. In short, there is only
one velocity to be calculated (peak velocity), the storm duration ("10 yr. 24 hour") is rhetoric
differentiating between different methods. Please find the Peak Velocity calculation submitted as
meeting the requirement to provide peak velocity calculations for the 10 year storm event (10 year 24
hour storm event language would be applicable if we used the SCS Method).
2. Please explain in detail how you derived the values for time of concentration used in the swale calculations.
Please document any assumptions regarding the height of the most remote point in the watershed, the length of
the flow path and how much of that flow path will be piped or channelized. These assumptions should necessarily
be based on the "worst -case" built -out scenario.

In order to give the "worst -case" built -out scenario would assume that the entire system is built via
pipe networks. Therefore it is required for the Designer to estimate length of the storm drain network
and the velocity within the pipes in order to arrive at a time to arrive downstream from the most
remote location. Please see the calculation below which was performed in -line to the hydraulic
analysis performed by Talbert & Bright while designing the downstream Detention Basin. The Tc used
by Talbert & Bright for the built -out basin was 180 minutes, which is greater than either scenarios
employed by Paramounte; therefore our calculation will give NCDENR a higher velocity due to a
shorter Tc.
Tc. Swale 1(Pipe Flow)
Hydraulic Length=
Pipe Slope=
n=
Diameter=
Velocity=
T=
Tc. Swale 2 (Pipe Flow)
Hydraulic Length=
Pipe Slope=
n=
Diameter=
Velocity=
T=
4800 If
0.002 ft/ft
0.013 (rcp)
4 ft (avg. size w/in basin)
0.97 fps
82 min.
7300 If
0.002 ft/ft
0.013 (rcp)
5 ft (avg. size w/in basin)
1.13 fps
108 min.
The velocity in the pipe is achieved using the empirical Manning's Equation which employs the pipe
diameter, pipe slope, and Manning's "n". Note that we could add overland -flow to the pipe system to
the Tc but if the velocity works for the lesser Tc then it will work as more Time is added on.
3. Please provide documentation of the 0.042 Mannings "n" value used in the swale calculations. A value of 0.042
seems high when compared to the tables published in V.T. Chow's Open Channel Hydraulics, 1959, McGraw-
Hill, and to the procedures for determining channel roughness coefficients described in the Erosion and Sediment
Control Planning and Design Manual (ESCPDM). The V.T Chow tables provide Manning's n-values for a wide
range of channel types. The n-value for an excavated, straight, uniform, earthen channel with short grass and a
few weeds has a range of 0.022 — 0.033. The Division uses a "normal" value of .027 which is supported by the
procedures described in the ESCPDM. Based on the Division's value, the resulting velocity in both swales is > 1
fps, but is less than the maximum permissible velocity of 5 fps for a grass -lined swale. However, this velocity
calculation is not based on the 10 year 24 hour storm, which will have a smaller intensity which will in all
likelihood, reduce the velocity below 1 fps.
• In effort to satisfy NCDENR requirements and also New Hanover County Stormwater Requirements to
be submitted and approved in the future, we used chart (Figure 60-4) within Section 60 — Open
Channel Design Procedures with -in the New Hanover County Storm Water Design Manual (See
attached). As you can see, we used "Curve D" to be in line with the 0&M agreement. With a product
of Velocity and Hydraulic Radius, we arrived at a Manning's n factor of 0.042 for vegetative
retardance.
Tim
Tim Clinkscales PE, PLS

DARAMOUNTE
11. M
PARAMOUNTE ENGINEERING, INC
5911 Oleander Drive, Suite 201
Wilmington, NC 28403
OFFICE: [phone]
CELL: [phone]
FAX: [phone]
From: Lewis,Linda [mailto:[e-mail]]
Sent: Wednesday, October 17, 2012 2:41 PM
To: Julie Wilsey
Cc: Tim Clinkscales; Russell, Janet
Subject: Additional Information / SW8 050547
Julie:
Attached please find my Express review comments for the subject project.
Linda

MCDENR
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Beverly Eaves Perdue Charles Wakild, P. E.
Governor Director
October 17, 2012
Julie Wilsey, Deputy Director
New Hanover County Airport Authority
1740 Airport Boulevard
Wilmington, NC 28405
Subject: Request for Additional Information — Express Review
Stonmwater Project No. SW8 050547
Wilmington International Airport
New Hanover County
Dear Ms. Wilsey:
The Wilmington Regional Office received an Express
Permit Application for Wilmington International Airport
preliminary review of that information has determined
complete. The following information is needed to con
The "for credit" grassed swales must meet two
provide a non -erosive velocity for the peak flow
provide a maximum velocity of 1 fps for the 10
calculations appear to provide only the 10 year
24 hour storm to demonstrate compliance with
you need to provide two velocity calculations, c
flow (to demonstrate nonerosive flow for the ch
one based on the less intense 10 year 24 hour
velocity is no more than 1 fps.)
Dee Freeman
Secretary
State Stormwater Management
on October 9, 2012. A
that the application is not
tinue the stormwater review:
separate velocity criteria: 1)
of the 10 year storm; and, 2)
year 24 hour storm. The
peak flow instead of the 10 year
the 1 fps velocity limit. Essentially,
ne based on the 10 year peak
osen swale lining and slope) and
storm (to demonstrate that the
2. Please explain in detail how you derived the values for time of concentration
used in the swale calculations. Please document any assumptions regarding the
height of the most remote point in the watershed, the length of the flow path and
how much of that flow path will be piped or channelized. These assumptions
should necessarily be based on the "worst -case" built -out scenario.
Please provide documentation of the 0.042 Mannings "n" value used in the swale
calculations. A value of 0.042 seems high when compared to the tables
published in V.T. Chow's Open Channel Hydraulics, 1959, McGraw-Hill, and to
the procedures for determining channel roughness coefficients described in the
Erosion and Sediment Control Planning and Design Manual (ESCPDM). The V.T
Chow tables provide Manning's n-values for a wide range of channel types. The
n-value for an excavated, straight, uniform, earthen channel with short grass and
a few weeds has a range of 0.022 — 0.033. The Division uses a "normal" value of
.027 which is supported by the procedures described in the ESCPDM. Based on
the Division's value, the resulting velocity in both swales is >1 fps, but is less
than the maximum permissible velocity of 5 fps for a grass -lined swale. However,
this velocity calculation is not based on the 10 year 24 hour storm, which will
have a smaller intensity which will in all likelihood, reduce the velocity below 1
fps.
Wilmington Regional Office
127 Cardinal Drive Extension, Wilmington, North Carolina 28405 ne
Phone: [phone] FAX: [phone] DENR Assis+tance:1.877-623-6748 No Carolina
Internet www wwaterquality.oig awngliff
An Fminl Meefimily 1 ATfirmafiv &Ann Fmnln—

Ms. Wilsey
October 17, 2012
Stormwater Application No. SW8 050547 Mod.
4. Bermuda is specified as the permanent grass type on the grassed swale
supplement forms submitted with the application, however, centipede is specified
on the plans. Centipede takes several years to establish. What sort of temporary
liner will be used in the meantime to prevent erosion? If the swales will be
seeded and not sodded, please provide additional swale calculations using the
peak flow from a 10 year storm and a Mannings "n" value for an excavated,
straight, uniform, earthen channel, recently completed (0.016 — 0.02) to
determine if a temporary liner is needed to prevent erosion.
5. The application erroneously indicates that the last permit issued for this project is
dated October 28, 2009. The current in -effect permit was issued on October 26,
2011. If the information you have provided in the most recent modified
application is based on making changes to the information in the 2009 permit,
please adjust accordingly in light of the 2011 permit.
6. Due to the design storm differences, and to be consistent with how the 2011
permit application was completed, and to cut down on the confusion, please list
the proposed drainage areas and built -upon areas for Phases I, II and III in
separate columns on the application.
7. Runways, taxiways, and any other areas that provide for overland stormwater
flow, promote infiltration and treatment of stormwater into grassed buffers,
shoulders, and grass swales are deemed permitted pursuant to the State's post -
construction stormwater requirements. Please request DWQ concurrence that
those areas of the airport that are to be "deemed permitted" meet the Session
Law requirements. Although the law did not mandate that an airport submit
anything or document compliance with the Session Law, it is my understanding
that not doing so could subject the Airport to civil penalties (NOV) and/or leave
them open to third party lawsuits. The burden of proof is on the airport, so
having a concurrence letter from the state would go a long way to making a case
that the airport is indeed in compliance with the Session Law. In order to provide
this concurrence, please delineate and identify the areas which are to be
"deemed permitted" under the Airport Session Law and demonstrate the required
overland sheet flow by providing a grading plan. Otherwise, an inspection of that
area will be conducted to determine compliance with the Session Law
requirements prior to approving the requested permit modification.
Please note that a revision to one number may have a domino effect on other numbers,
which may require revision of the applications, calculations, supplements, plans, details,
and associated documentation. Please verify all numbers are correct to ensure
consistency in the application documents.
Please note that this request for additional information is in response to a preliminary
review. The requested information should be received in this Office prior to October 25,
2012, or the application will be returned as incomplete. The return of a project will
necessitate resubmittal of all required items, including the application fee.
If you need additional time to submit the information, please mail, email or fax your
request for a time extension to the Division at the address and fax number at the bottom
of this letter. The request must indicate the date by which you expect to submit the
required information. In the Express program, no more than 2 time extensions may be
granted, for a total of 10 days.
Page 2of3

Ms. Wilsey
October 17, 2012
Stormwater Application No. SW8 050547 Mod.
The construction of any impervious surfaces, other than a construction entrance under
an approved Sedimentation Erosion Control Plan, is a violation of NCGS 143-215.1 and
is subject to enforcement action pursuant to NCGS 143-215.6A. The proposed
modification may not be constructed until the permit modification is approved and
issued.
Please reference the State assigned project number on all correspondence. Any
original documents that need to be revised have been sent to the engineer or agent. All
original documents must be returned or new originals must be provided. Copies are not
acceptable. If you have any questions concerning this matter please feel free to call me
at [phone] or email me at Iinda.lewisCaD-ncdenr.gov
Sincerely,
Linda Lewis
Environmental Engineer III
GDS/arl: S:MMStormwaterVermits & Projects120051050547 HD1201210 addinfo 050547
cc: Tim Clinkscales, P.E., Paramounte Engineering
Wilmington Regional Office Stormwater File
Page 3 of 3

PARAMOU-NTE
E N G 1 N E E M 1 N V, 1 N C.
9 9 9 1 1 OLEANDER DRIVE, SUITE 20 1
W I L M I N G T O N, NC 2 8 4 0 3
9 1 0- 7 9 1- 6 7 0 7( O) 9 1 0- 7 9 1- 6 7 6 0 ( F)
L E T T E R 0 F T R A N 9 M T T T A T
To:
NCDENR-Land Quality Section
Date
1 10/09/2012
127 Cardinal Drive Extension
Wilmington, NC 28405
Re:
Wilmington International Airport
Stormwater MOD & Pre -Treatment
Attu:
Proect No.
I 12212. PE
e are sencli ® Originals
he following items: ❑ Correspondence
® Prints ❑ Shop Drawings ❑ Calculations
® Plans ❑ Specifications ® Other as listed below
Quantity
Date
Dwg. No.
Description
2
Plans (Final Design — Not Released For Construction)
1
Stormwater Narrative w/ Calculations
1
Check for Express Review Fee ($4000.00)
1
Stormwater Permit Application Form (Original & Copy)
1
Grassed Swale Basin Supplement (Original)
1
Grassed Swale O&M Agreement (Original)
ssue Status ® For Approval ❑ As Requested ❑ Construction ❑ Bid
❑ For Your Use ❑ For Review and Comment ❑ Approved as Noted ❑ See Remarks
tion Taken: ❑ No Exceptions Taken ❑ Make Corrections Noted ❑ Amend & Resubmit
❑ Rejected - See Remarks ❑ Approved as Submitted ❑ Other Im 0 0- - M ' toil
W.VDmarks: 1
Chris Millis
RR-4
OCT 0,,9 2012
BY: