SW8050547_Historical File_20050615

140F WATER Michael F. Easley, Governor
_10� �� William G. Ross, Jr., Secretary
North Carolina Department of Environment and Natural Resources
Q "C' Alan W. Klimek, P.E. Director
Division of Water Quality
June 15, 2005
Mr. Jon W. Rosborough, Airport Director
New Hanover County Airport Authority
1740 Airport Boulevard
Wilmington, NC 28405
Subject: Stormwater Permit No. SW8 050547
Wilmington Intl. Airport SW Management, Phase I: Extended Dry Detention Basin#1
High Density Project
New Hanover County
Dear Mr. Rosborough:
The Wilmington Regional Office received a complete Stormwater Management Permit Application for
Wilmington International Airport SW Management, Phase I on June 13, 2005. 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 Permit No. SW8 050547 dated.
June 15, 2005, for the construction of the subject project.
This permit is for the stormwater treatment of a designated, high -density pocket consisting of 150 acres
with an initial configuration for Basin No.1 development, in accordance with Permit No. SW8 040836 for
the Airport Master Stormwater Plan. Permit No. SW8 050547 for Phase I shall be effective from the
date of issuance until June 15, 2015, and shall be subject to the conditions and limitations as specified
therein. Please pay special attention to the Operation and Maintenance requirements in this permit.
Failure to establish an adequate system for operation and maintenance of the stormwater management
system 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 upon written request within thirty (30) days following receipt of this
permit. This request must be in the form of a written petition, conforming to Chapter 150E of the North
Carolina General Statutes, and filed with the Office of Administrative Hearings, P.O. Drawer 27447,
Raleigh, NC 27611-74,47. 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 Paul
Bartlett, or me at [phone].
Since �
Ed C-e
Regional Supervisor
Surface Water Protection Section
ENB/ptb: S:1WQStSTORMWATIPERMIT1050547
cc: Talbert & Bright, Inc.
Tony Roberts, New Hanover County Building Inspections
City of Wilmington Stormwater Services
Beth E. Wetherill, New Hanover County Engineering
Division of Coastal Management
Paul T. Bartlett, P.E.
Wilmington Regional Office
Central Files
North Carolina Division of Water Quality 127 Cardinal Drive Extension Phone [phone] Customer Servicel-877-623-6748
Wilmington Regional Office Wilmington, NC 28405-3845 FAX [phone] Internet: h2o.enr.state,nc.us One
North Carolina
An Equal Opportunity/Affirmative Action Employer— 50% Recycledl10% Post Consumer Paper )VIdurld'/

State Stormwater Management Systems
Permit No. SW8 050547
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
Jon W. Rosborough and New Hanover County Airport Authority
Wilmington International Airport Stormwater Management
Phase 1, Extended Dry Detention Basin No. 1
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 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, 2015, 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 1.6 on page 3 of this permit. The initial
configuration of the sto �•nwater control has been designed to handle the runoff
from 4,247,100 square feet of impervious area.
3. The tract `will be limited to the amount of built -upon area indicated on page 3 of
this permit, and per approved plans.
4. All stormw'tater collection and treatment systems must be located in either
dedicated common areas or recorded easements. The final plats for the project
will be recorded showing all such required easements, in accordance with the
approved plans.
Page 2 of 8

State Stormwater Management Systems
Permit No. SW8 050547
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. FAA
requirements prohibit standing water (i.e., permanent pools) and stipulate that
the design storm must be fully drained within 48 hours. The approved plans
include a low flow device to meet these FAA requirements, and, as a
consequence, the approved plans do not include a permanent pool at the low
flow outlet or sediment storage below the low flow outlet.
6. The following design criteria have been provided in the extended dry detention
basin and must be maintained at design conditions:
a. Drainage Area, 9cres: 150
Onsite, ft : 6,534,000
Offsite, ft2: None
b. Total Impervious Surfaces, ft2: 4,247,100
C. Design Storm, inches: 1.0
d. Basin Bottom Elevation, feet: 7 - 13
Y
e. TS;S removal efficiency: 50
(Required Additional BMP to be provided by tributary projects.)
f. Storage Elevation, FMSL: 9.87
g. Storage Surface Area, ft2: 77,200
h. Permitted Detention Volume, ft3: 66,734
i. Sediment Storage Volume, ft3: 20,604
j. Seasonal High Water Table, FMSL: 6.0
k. Controlling Orifice: 8.0"0 pipe (3.75"0 low flow)
I. Drawdown Time for 8.0"0 orifice, hrs: 48
M. Receiving Stream/River Basin: Smith Creek / Cape Fear
c
n. Stream Index Number: 18-74-63
o. Classification of Water Body: "C; Sw"
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.
2. During construction, erosion shall be kept to a minimum and any eroded areas of
the system will be repaired immediately.
Page 3 of 8

State Stormwater Management Systems
Permit No. SW8 050547
3. 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. Sedirrient 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.
4. 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.
5. The facilities shall be constructed as shown on the approved plans. This permit
shall become voidable unless the facilities are constructed in accordance with
the conditions of this permit, the approved plans and specifications, and other
supporting data.
6. Upon completion of construction, prior to issuance of a Certificate of Occupancy,
and prior. 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.
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 stormwater facilities shall be maintained via appropriate
easements 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
sto -mwater management measures, built -upon area, details, etc.
b. Project name change.
C. Transfer of ownership.
d. Redesign or addition to the approved amount of built -upon area or to the
drainage area.
e. Further subdivision, acquisition, lease or sale of all or part of the project
area. The project area is defined as all property owned by the permittee,
for which Sedimentation and Erosion Control Plan approval or a CAMA
Major permit was sought.
f. Filling in, altering, or piping of any vegetative conveyance shown on the
approved plan.
Page 4 of 8

State Stormwater Management Systems
Permit No. SW8 050547
10. The permittee shall submit final site layout and grading plans for any permitted
future areas shown on the approved plans, prior to construction.
11. A copy of the approved plans and specifications shall be maintained on file by
the Permittee for a minimum of ten years from the date of the completion of
construction.
12. 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 copies of revised plans and certification in writing to the Director
that the changes have been made.
III. GENERAL CONDITIONS
This permit is not transferable except after notice to and approval by the Director.
In the event of a change of ownership, or a name change, the permittee must
submit a formal permit transfer request to the Division of Water Quality,
accompanied by a completed name/ownership change form, documentation
from the parties involved, and other supporting materials as may be appropriate.
The approval of this request will be considered on its merits and may or may not
be approved. The permittee is responsible for compliance with all permit
conditions until such time as the Division approves the transfer request.
2. 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.
3. 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.
4. In the event that the facilities fail to perform satisfactorily, including the creation
of nuisance conditions, 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
filinq 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 mast 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.
Page 5 of 8

State Stormwater Management Systems
Permit No. SW8 050547
9. The permittee shall notify the Division any name, ownership or mailing address
changes within 30 days.
Permit issued this the 15th day of June 2005.
0
NORTH CAROLINA ENVIRONMENTAL MANAGEMENT COMMISSiON
Hian vv. KlimeK, N.L., uirector
Division of Water Quality
By Authority of the Environmental Management Commission
Page 6 of 8

State Stormwater Management Systems
Permit No. SW8 050547
Wilmington International Airport Stormwater Management - Phase I, Extended Dry
Detention Basin No. 1
Stormwater Permit No. SW8 050547
New Hanover County
Designer's Certification
I, , 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 8

State Stormwater Management Systems
Permit No. SW8 050547
Certification Requirements:
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 roof drains are located such that the runoff 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. Trash rack is provided on the outlet/bypass structure.
8. All slopes are grassed with permanent vegetation.
9. VeQetated 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 devices are correctly sized per the approved plans.
13. All required design depths are provided.
14. All required parts of the system are provided, such as an outlet structure
and a forebay.
15. The required system dimensions are provided per the approved plans.
cc: NCDENR-DWQ Regional Office
Tony Roberts, New Hanover County Building Inspections
Page 8 of 8

OFFICE USE aivI.:
Date Received
Fee Paid
Permit Number
5 Z? 1 Ds
4W0 - 2
S1N 5b
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. Applicants name (specify the name of the corporation, individual, etc. who owns the project):
2. Print Owner/Signing Official's name and title (person legally responsible for facility and compliance):
3. Mailing Address for person listed in item 2 above:
1740 Airport Blvd
City:_ W i l m i n?t o n State: NC Zip: 28405
Telephone Number: f 910 1 3 41- 4 3 3 3 E x t 1001
4. Project Name (subdivision, facility, or establishment name - should be consistent with project name on plans,
specifications, letters, operation and maintenance agreements, etc.):
W jLmingon International Airport Stormwater Management - Phase I
(Extended Dry Detention Basin No 1
5. Location of Project (street address):
City: Wilmi ngton County:
6. Directions to project (from nearest major intersection):
MAY .2 8 Z005
7. Latitude: 3 4 ° -1 6 ' -14 '! N Longitude: 7 7 ° - 5 4 ' - 0 9 " W of project
8. Contact person who can answer questions about the project:
Name: Eric S t umph Telephone Number: L910 _) 7 6 3- 5 3 5 0
Talbert & Bright, Inc. AND Julie Wilsey, Deputy Director
Wilmington -International Airport
II. PERMIT INFORMATION: 910 - 3 41- 4 3 3 3
1. Specify whether project is (check one): x_New Renewal Modification
Refer to Master Plan Permit No. SW8 040836.
Form SWU-101 Version 3.99 Page 1 of 4

2. If this application is being submitted as the result of a renewal or modification to an existing permit, list the
existing permit number and its issue date (if known)
3. Specify the type of project (check one):
Low Density X_High Density Redevelop General Permit Other
(Pocket)
4. Additional Project Requirements (check applicable blanks):
_CAMA Major X_Sedimentation/Erosion Control 404/401 Permit X NPDES Stormwater
Information on required state permits can be obtained by contacting the Customer Service Center at
1-877-623-6748.
III. PROJECT INFORMATION
1. In the space provided below, summarize how stormwater will be treated. Also attach a detailed narrative
(one to two pages) describing stormwater management for the project.
Extended Dry D_ n inn will hp used to treat orm water (50%
removal effirienvy) Tribunary projects will provide supplemental
2. Stormwater runoff from this project drains to the Cape Fear River basin.
3. Total Project Area: 15 0 acres * 4. Project Built Upon Area: 65 N6
* Interim Basin Tributary
5. How many drainage areas does the project have? 1 area. Future improvements /
expansion work expected to allow
6. Complete the following information for each drainage area. If there are more than two drainage areas in the increased
project, attach an additional sheet with the information for each area provided in the same format as below. tributary
area.
Basin Information
Drainage Area 1
Drainage Area 2
Receiving Stream Name
Smith Creak
Receiving Stream Class
C • SW
Drainage Area
150 acres
Existing Impervious* Area
16.2
Proposed Impervious *Area
97.5 acres
% Impervious* Area (total)
65
Impervious* Surface Area
Drainage Area 1
Drainage Area 2
On -site Buildings
See Note_
On -site Streets�-
On-site Parking
On -site Sidewalks
Other on -site
97.5 acres
Off -site
I 1
Total: 97.5 acres
I Total: 1
" Impervious area is defined as the built upon area including, but not limited to, buildings, roads, parking areas,
sidewalks, gravel areas, etc.
NOTE: Distribution of permitted tributary impervious
surfacing unknown at this time.
Form SWU-101 Version 3.99 Page 2 of 4

How was the off -site impervious area listed above derived? Tributary art -.a is ent it m l y
on —site.
IV. DEED RESTRICTIONS AND PROTECTIVE COVENANTS
The following italicized deed restrictions and protective covenants are required to be recorded for all
subdivisions, outparcels and future development prior to the sale of any lot. If lot sizes vary significantly, a table
listing each lot number, size and the allowable built -upon area for each lot must be provided as an attachment.
1. The following covenants are intended to ensure ongoing compliance with state stormwater management permit number
as issued by the Division of Water Quality. These covenants may not be
changed or deleted without the consent of the State.
2. No more than square feet of any lot shall be covered by structures or impervious materials.
Impervious materials include asphalt, gravel, concrete, brick, stone, slate or similar material but do not include wood
decking or the water surface of swimming pools.
3. Swales shall not be filled in, piped, or altered except as necessary to provide driveway crossings.
4. Built -upon area in excess of the permitted amount requires a state stormwater management permit modification prior to
construction.
5. All permitted runoff from outparcels or future development shall be directed into the permitted stormwater control
system. These connections to the stormwater control system shall be performed in a manner that maintains the integrity
and performance of the system as permitted.
By your signature below, you certify that the recorded deed restrictions and protective covenants for this project
shall include all the applicable items required above, 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 State, and that they will be recorded prior to the sale of any lot.
V. SUPPLEMENT FORMS
The applicable state stormwater management permit supplement form(s) listed below must be submitted for each
BMP specified for this project. Contact the Stormwater and General Permits Unit at [phone] for the status
and availability of these forms.
Form SWU-102
Wet Detention Basin Supplement
Form SWU-103
Infiltration Basin Supplement
Form SWU-104
Low Density Supplement
Form SWU-105
Curb Outlet System Supplement
Form SWU-106
Off -Site System Supplement
Form SWU-107
Underground Infiltration Trench Supplement
Form SWU-108
Neuse River Basin Supplement
Form SWU-109
Innovative Best Management Practice Supplement
Form SWU-101 Version 3.99 Page 3 of 4

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. The complete application package should be
submitted to the appropriate DWQ Regional Office.
Please it dicaie that you have provided the following required information by initialing in the space provided
next to each item.
• Original and one copy of the Stormwater Management Permit Application Form
• One copy of the applicable Supplement Form(s) for each BMP
• Permit application processing fee of $420 (payable to NCDENR)
• Detailed narrative description of stormwater treatment/management
• Two copies of plans and specifications, including:
- Development/Project name
- Engineer and firm
-Legend
- North arrow
- Scale
- Revision number & date
- Mean high water line
- Dimensioned property/project boundary
- Location map with named streets or NCSR numbers
r
r
- Original contours, proposed contours, spot elevations, finished floor elevations
- Details of roads, drainage features, collection systems, and stormwater control measures
- Wetlands delineated, or a note on plans that none exist
Existing drainage (including off -site), drainage easements, pipe sizes, runoff calculations
Drainage areas delineated
Vegetated buffers (where required)
VII. AGENT AUTHORIZATION
If you wish to designate authority to another individual or firm so that they may provide information on your
behalf, please complete this section.
Eric M. Stumph, P.E.
Designated agent (individual or firm): Talbert & Bright, ght Inc
Mailing Address: 4 810 Shelley Drive
City: Wilmington State: NC Zip:
Phone: (_ 910 ) 763-5350
VIII. APPLICANT'S CERTIFICATION
I, (print or type name of person listed in General Information, item 2) Jon W . Rosboro i gh
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 15A
NCAC 2H .10D _
Dater
Form SWU-101 Version 3.99 Page 4 of 4

Permit No. Svc q 06 C)
(Po be provided by DWQ)
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
EXTENDED DRY DETENTION BASIN SUPPLEMENT
This form may be photocopied for use as an original.
DWO Stormwater Management Plan Review:
A complete stormwater management plan submittal includes a dry detention basin supplement for each basin,
design calculations, plans and specification showing all basin and outlet structure details, and a fully executed
operation and maintenance agreement.
I. PROJECT INFORMATION (Please complete the following information):
Project Name: Wi 1mi ntTtnn Tntarnati anal Ai-r13p�i--( StQrmwAtpr ManarYt=mcnt Phaca I )
Contact Person: Fri r M_ Stumph, P.E. Phone Number: 91 0- 7 6 3- 5 3 5 0
For projects with multiple basins, specify which basin this worksheet applies to:Rxtended DrybDetention
Design Storm: (Please mark one) ❑ 1 yr, 24 hr storm =" storm Basin No. 1.
150 acres P -
Drainage Area: 6, 5 3 4, 0 0 0 square feet
1" R fall Runoff
Require3 olume: 9 4 ,92.5 cubic feet
Basin Dimensions: -.'(Irregular Shape)
Built -upon Area: 4,247,100 square feet
SHWT elevation: 6 FMSL
Bottom Elevation: 7, t o 13feet, MSL Area:110 O ft long x 3 5 0 ft wide = 385,000 ft2 (A - 4 2)
Storage Elevation: 9, 8 7 feet, MSL Area:10 0 0 ft long x 7 7.2 ftwide= 77.200 ft2 (A- 4 2)
(A-3)
Detention Volume Provided: 66,734 cubic feet ( Peak Storage, Routed 1" Rainfall)
Sediment Storage Provided: 2 0 , 6 04A- 3) cubic feet (Equivalent to 20% of the detention volume)
Sediment Storage Elevation: 10. 15A- 3) FMSL
Drawdown Orifice: ``3.7 5 "d IN 811 PVC (Please indicate size and type of orifice)
Required Additional $MP to achieve a total of 85% TSS (check one):
❑Grassed swale ❑Vegetated Filter 91 Other To be provided by tributary
projects.
(A-1) -Denotes Stormwater Management Narrative and
,computations, Appendix A, Page A-1.

Permit No. SW 9 D6Q54�1
(To be provided by DWQ)
H. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices Manual
(N.C. Department of Environment, Health, and Natural Resources, November, 1995) and Administrative
Section 15A NCAC 2H.1008.
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the;agent may initial below. If a requirement has not been met, attach written
justification.
Please initial in the blanks prior to each requirement.
a. The basin captures the runoff from the 1 year, 24 hour storm and releases it over a period of 48
hours
� tb OR the basin captures the runoff from the 1 inch storm and allows it to draw down over a period
of 2-5 days.
`-� C. The minimum flow length ratio is 3:1, L:W.
d. Basin sideslopes are no steeper than 3:1.
NA e. A small permanent pool has been provided at the outlet to reduce clogging. Inconsistent with
p p pFAA wildlife
f. Cleanout access has been provided, sufficient for heavy equipment. Hazards Advisory
Circular
A.drain has been provided which will completely empty the basin for cleanout.
Sufficient volume has been provided for any local government peak flow requirements.
�i. If the basin was used during construction as a sediment basin or trap, it must be cleaned out to
design specifications prior to operation as a dry detention basin.
�. A vegetation plan has been prepared by a N.C. licensed professional. Consideration must be
given to the grasses specified due to the frequent inundation.
�k. The basi6nust be stabilized within 14 days of construction.
The design provides for the sediment storage in addition to the detention volume that is equal to
�`� 20% of the detention volume.
,e'm. Inlet and outlet channels have been protected from scour during high flows from large storms.
�. In areas of easily erodible soils, an additional plunge pool at the inlet has been provided, or riprap
is used as an energy dissipator.
—L�—"o. A forebay�to capture sediment is recommended to make cleanout easier.
. The basin.is located in uncompacted natural soils.
. The seasonal high water table is located at least 1 foot below the bottom of the extended dry
detennon'basm.
NA r. An additional BMIP (such as a swale or vegetated filter) has been designed to ;,crate in
conjunction with this dry detention basin to meet the required minimum 85% TSS removal.
REQUIREMENT FOR TRIBUTARY PROJECTS.

Permit No.
(To be provided by DWQ)
III. EXTENDED :DRY DETENTION OPERATION AND MAINTENANCE AGREEMENT
The extended dry detention system is defined as the dry detention basin, forebay, and the required additional
BMP.
This system (check ®sae) ❑ does gI does not incorporate a vegetated filter.
This system (check one) f1does ❑ does not incorporate non-integrated pretreatment.
Maintenance activities shall be performed as follows:
1. All grassed areas of the basin shall be mowed at least twice annually, more frequently as needed.
2. Debris must be removed from the basin, outlet and orifice whenever it accumulates or at least twice
annually.
3. Annually- inspect the basin after a rain event to ensure it is functioning properly.
4. Repair any erosion of the side slopes and around the inlets and outlet immediately.
5. Accumulated sediment shall removed if it has reduced the available volume to 75% of the original
depth.
6. The emergency' spillway shall be kept in good working order.
7. Woody vegetation shall be removed from the banks.
8. Any areas of the system found to be deficient shall be repaired or replaced to design standards.
9. Written records of the inspections and maintenance activities shall be kept on file.
I acknowledge and agree by my signature below that I am responsible for the performance of the above
maintenance procedures for the dry detention basin. I agree to notify DWQ of any problems with the system
or changes in the name of the project, responsible party, or address.
Printname: Jon W_:: Rosborough Title: Airport Director
Address: 1740 Ai wort Blvd-; Wilmington,_ NQ 28405
Phone: - 4` 10 01 Fax: [phone]
Signature: 1AA- c } Date: /.:,q 6
I, m`s's �lL , a Notary Public for the State of
M0r-� k eft ry i "c A , County of nr%sloLi
do hereby certify that To#, L anl� personally appcarcd before me this
the day of MAQ and acknowledge the due execution
of the forgoing dry detention basin maintenance requirements. Witness my hand and official seal,
I _ SSA-. &
g.
Signature j/�0T4�
My Commission expires /v -fig ' p�
Z •o
GeL1G
'• UN'C'

Wilmington International Airport
Stormwater Management — Phase I
Extended Dry Detention Basin No. 1
Stormwater Permit No. SW8 050547
New Hanover County
Designer's Statement
State Stormwater Management Systems
41. v —
13
D%
Talbert & Bright, Inc., having been authorized to observe full time the construction of the project,
"Wilmington International Airport, Stormwater Management — Phase I,"
for the New Hanover County Airport Authority, hereby states that, to the best of our ability, due
care and diligence was used in the observation of the project construction and that the
construction was observed to have been built in substantial conformance with the approved
plans and specifications and the project design intent.
The attached .checklist of items is included in this statement.
Noted deviations from approved plans and specifications:
A field change was made to the location/alignment of the maintenance access road adjacent to
low flow outlet channel. ,,�•••••••.�,,
Talbert & Bright, Inc.
4810 Shelley Drive
Wilmington, North Carolina 28405
[phone]
By:
� N
a 4,I
�i�i`,`.•�6�<40 sot
.r
Al
Date: ?" 2.7— v
c M. Stumph, ., Project Manager
North Carolina Professional Engineer No. 024169

State Storm%,--,4er Management Systems
Permit No. SW8 050547
Certification Requirements: JUL 2 8 Z006
4, 1. The drainage area to the -system contains approximately the permitted
acreage.
�L4- 2. The drainage area to the system contains no more than the permitted
amount of built -upon area.
L3. All the built -upon area associated with the project is graded such that the
/ runoff drains to the system.
AJ/4 4. All roof drains are located such that the runoff is directed into the system.
5. The outlet/bypass structure elevations are per the approved plan.
The outlet structure is located per the approved plans.
�. Trash rack is provided on the outlet/bypass structure.
rIslopes are grassed with permanent vegetation.
-
All Vegetated slopes are no steeper than 3:1.
0. The inlets are located per the approved plans and do not cause short-
circuiting.of the system.
�1. Thq permitted amounts of surface area and/or volume have been
provided.
�. Required drawdown devices are correctly sized per the approved plans.
All required design. depths are provided.
4. All required parts of the system are provided, such as an outlet structure
and a forebay.
5. The required system dimensions are provided per the approved plans.
cc: NCDENR:,DWQ Regional Office
Tony Roberts, New Hanover County Building Inspections
17-1
Note to Checklist Items 1 through 4:
This project constructed a centralized stormwater management facility (Extended Dry Detention
Basin No. 1) intended to serve multiple future development projects. Those future projects, in
aggregate, will physically establish the drainage area and built upon area tributary to EDDB No.
1, including grading and drainage measures necessary to direct runoff from the built upon areas
(including roof areas) to the facility.
Page 8 of 8

'- & BRIGHT
June 13, 2005
Mr. Paul T. Bartlett, P.E.
North Carolina Department of Environment and Natural Resources
127 Cardinal Drive Extension
Wilmington, NC 28405
RE: Wilmington International Airport
Stormwater Management — Phase I
AIP 3-37-0084-34; TBI No. 3301-0501
NCDENR DWQ #SW8 050547 _ UCE-1— M
Dear Paul: � 7
In response to your letter of June 8, 2005 and our telephone conversation of June 9, 2005, we
have prepared a 3 sheet Impervious Area plan which depicts existing impervious surfacing within
the 150 acre tributary area associated with Extended Dry Detention Basin No. 1. Impervious
surfacing is shown hatched and the most recent County aerial photography is plotted as
background. We have annotated the plan with approximate dimensions of large impervious areas
along with roadway widths. Two sets of the plan are enclosed for your use.
As discussed, the overhead power line which crosses Extended Dry Detention Basin No. 1 is a
service line which provides electrical power to a visual approach aid for Runway 6. No other
customers or facilities are served by the line. The line has been in place for many years.
Information regarding the configuration of a right-of-way or easement specific to this line is not
readily available. The construction contractor's responsibilities with respect to this line and
numerous other utility lines in the project area are spelled out in the specifications and plan notes.
The line itself is clearly shown and labeled on the plans. Following construction, maintenance
operations will be under the direction of Mr. Whitney Preace, Facilities Manager at the airport,
who is familiar with the line in question as well as other utilities at the airport and who has
extensive construction experience.
Also as discussed, we do not have a soils report addressing the seasonal high water table at
Extended Dry Detention Basin No. 1. Excavation of the 11 acre basin as a borrow source has
been underway for several months and is now essentially complete. The basin was excavated in
the dry with little in the way of dewatering efforts. Except for minor localized seepage in one
area along the basin perimeter, no groundwater effects have been observed.
ENGINEERING & PLANNING CONSULTANTS
WWW.TALBEP,TAN DBRIGHT.COM
4810 SHELLEY DRIVE WILMINGTON, NC 28405 910.763.5350 FAX [phone]
WILMINGTON, NORTH CAROLINA • CHARLOTTE, NORTH CAROLINA • RICHMOND, VIRGINIA

Mr. Paal J . Bartlett, P.E.
Page 2
We trust that this supplemental information adequately addresses your letter of June 8, 2005.
Please call me if you have any further questions or need additional information during the course
of project review.
Sincerely,
P
Eric M. Stumph, P.E.
Enclosures
c: Ms Julie Wilsey, Deputy Airport Director (w/enc.)

State of North Carolina
Department of Environment and Natural Resources
Wilmington Regional Office
Michael F. Easley, Governor
FAX COVER SHEET
William G. Ross, Jr., Secretary
Date: 6/8/05 No. of Pages: 3 (Incl. Cover)
To: Eric Stumph From: Paul Bartlett
Company: Talbert & Bright Water Quality Section - Stormwater
FAX #: [phone] FAX #: [phone]
Phone #: [phone]
DWQ Stormwater Project Number: SW8 050547
Project Name: Wilmington Intl. Airport Stormwater Management - Phase
MESSAGE:
Eric,
A Request for Additional Information is attached
Rosborough, and a copy will be mailed to you.
0
The original will be mailed to Mr.
ENB1ptb: S:IWQSISTORMWATERIADDINF0120051050547
127 Cardinal Drive Extension, Wilmington, NC 28405-3845 Telephone [phone] FAX [phone]
An Equal Opportunity Affirmative Action Employer

�9F W A Tfi9P Michael F. Easley, Governor
�02 William G. Ross, Jr., Secretary
North Carolina Department of Environment and Natural Resources
Alan W. Klimek, P.E. Director
Division of Water Quality
June 8, 2005
Mr. Jon Rosborough, Director
New Hanover County Airport Authority
1740 Airport Boulevard
Wilmington, NC 28405
Subject: Request for Additional Information
Stormwater Project No. SW8 050547
Wilmington International Airport Stormwater Management — Phase I
(Extended Dry Detention Basin No. 1)
New Hanover County
Dear Mr. Rosborough:
The Wilmington Regional Office received a Stormwater Management Permit Application for
Wilmington International Airport Stormwater Management — Phase I on May 28, 2005 for a
scheduled review date of June 7, 2005. A preliminary review of that information has
determined that the; application is not complete. The following information is needed to
continue the storm iLter review:
C
1. Please provide a plan sheet or sheets of the proposed drainage area that dimensions,
/C� 0 at a readable scale, the existing and proposed (as currently projected) buildings,
r parking areas, roadways, and other impervious structures to provide a current baseline
of built -upon area.
Please delineate the right-of-way for the Overhead Electrical Line adjacent to the
G�3(bay Berm. Please add a note that any right-of-way access involving maintenance
or other activities will be coordinated with the responsible electrical utility.
p- IL Please provide a soils report to confirm that the seasonal high water table is 1' minimum
�1/ ( ow the bottom of the extended dry detention basin.
Please note that this' request for additional information is in response to a preliminary review.
P rY
The requested information should be received by this Office prior to June 16, 2005, or the
application will be returned as incomplete. The return of a project will necessitate resubmittal of
all required items, including the application fee.
A
If you need additional time to submit the information, please mail 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. The
Division is allowed 90 days from the receipt of a completed application to issue the
permit.
North Carolina Division of Water Quality 127 Cardinal Drive Extension Phone [phone] Customer Servicel-877-623-6748 One
Wilmington Regional Office Wilmington, NC 284053845 FAX [phone] Internet: h2o.enr.state.nc.us NorthCaro/lina
An Equal OpportunitylAfrirmative Action Employer— 50% Recycled110% Post Consumer Paper Nat al

Mr. Jon W. Rosborough
June 8, 2005
Stormwater Application No. SW8 050547
The construction ofany 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.
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].
Since ly,
:t
Paul T. Bartlett, P.E.
Environmental Engineer
f
ENB/ptb: S:\WM\STORMWATER\ADDINFO\2005\050547
cc: Eric Stumph, P.E., Talbert & Bright
Paul Bartlett
I
6

P. 1
* * * COMMUNICATION RESULT REPORT ( JUN. 8.2005 5:08PM ) * * *
TTI NCDENR WIRO
FILE MODE OPTION ADDRESS (GROUP) RESULT PAGE
-------- ------
646 MEMORY TX 9-7626281 OK P. 3/3
REASON FOR ERROR
E-1) HANG UP OR LINE FAIL E-2) BUSY
E-3) NO ANSWER E-4) NO FACSIMILE CONNECTION
State ofi North Carolina
Department of Environment and Natural Resources
Wilmington Regional Offioe
Michael F. Easley, Govemor
FAX COVER SHEEN"
William G. Ross, Jr., Secretary
Date: 6/8l05 No, of Pages: 3 (Ind. Cover)
To; Eric Stumph From: Paul Bartlett
Company: Talbert & Bright Water Quality Section - Stormwater
FAX 9: 910-762-6281 FAX 4: 910-360-2004
Phone #: [phone]
DWQ Stormwater project Number: 8W8 050547
Project Name: Wilmington Intl. Airport Stormwater Management - Phase I
MESSAGE:
Eric,
A Request for Additional Information is attached.
Rosborough, and a copy will be mailed to you.
The original will be mailed to Mr.

May 26, 2005
Mr. Cameron Weaver
North Carolina Department of Environment and Natural Resources
127 Cardinal Drive Extension
Wilmington, NC 28405
RE: Wilmington International Airport
Stormwater Management — Phase I v 6 l 7
AIP 3-37-0084-34
TBI No. 3301-0501 �.� - Y
9?j
Dear Cameron:
Enclosed please find the Stormwater Management Permit Application package for the
Stormwater Management — Phase I project at the Wilmington International Airport. We
understand that the project has been scheduled for review on June 7, 2005 under the express
permit program. The following materials are enclosed:
Application Form, With Extended Dry Detention Basin Supplement (original)
Application Form, With Extended Dry Detention Basin Supplement (copy)
Express Processing Fee (check for $4,000.00)°
Project Narrative and Computations (2 copies) MA, y ��
Project Plans and Specifications (2 sets) _
Please call me if you have any questions or need additional information.
Sincerely,
` ,Eric M. St ph, P.E.
Enclosures
c: Ms Julie Wilsey, Deputy Airport Director (w/enc.)
ENGINEERING & PLANNING CONSULTANTS
WWW.TALBERTANDBRIGHT.COM
4810 SHELLEY DRIVE WILMINGTON, NC 28405 910.763.5350 FAX [phone]
WILMINGTON, NORTH CAROLINA • CHARLOTTE, NORTH CAROLINA • RICHMOND, VIRGINIA

��
NCDENR
North Carolina Department of Environment and tural Resources
127 Cardinal Drive Extension, Wilmington, NC 28405 (910 5-39oo FAX [phone]
Request for Express Per it Review G /_7
FILL-IN all Information below and CHECK uired Permits). i
FAX to Cameron Weaver along with a Mottye and vicinfiV ma of the prc ect location. a
Projects must be submitted by 9:00 A.N. on the review date, u iless prior arras reffieft are made.
/ I
DATE 05/25/2005
tti
APPLICANT Name Jon Rosborguoh. Airport Director
Company New Hanover County Airport Authority
Address 1740 Ai ort Blvd. City Wilmington NC Zip 28405 County New Hanover
Phone [phone] Fax [phone] Email imsbor®u h fi ilm.wm �
I
PROJECT Name Stormwater Management — Phase I Extended Dly Detention Basin No.1 and Conve slice Pipeline)
ENGINEER/CONSULTANT Eric M. Stumph. P.E.
Company Talbert & Br_'ight, Inc.
Address 4810 Shelley Drive City— Wilmington Zip 8105 County Ne
Hanover
Phone [phone] Fax [phone] Email esturn
bh @ tbiilm.com
❑ STREAM OMINAnoN CERTIRCATiON
Z STORMWATER ❑ Low Density ® High Densi
-Detention Pond
' ❑ Off siteT;
❑ Low Density -Curb & Gutter ❑ High Densl
-Infiltration-
The Soils Scientist must visit the site to confi
The Designer's Certification and recorded deed
the soils prior to
restrictions must
submittal,
be submitted.
❑ COASTAL ❑ Excavation & Fill ❑ Bridges &
ulverts
0 Structures Information
MANAGEMENT ❑ Upland Development ❑ Marina De
lopment
❑ Urban V aterfront
❑ LAND QUALITY ❑ Erosion and Sedimentation Control Plan
I
❑ WETLANDS (401 ❑ No Wetlands on Site (letter from COE
❑ Wetlands Delineated=
JD
❑
Greater than 0.1 AC Wetlands Impacted
❑ Judsdictior
al Determination has been done
❑
Less than 0.1 AC Wetlands Impacted
❑ Greater th
n 0.5 AC Wetlands Impacted
The legislation allows additional fees, not to exceed 50% of the !rig*
apress Review
permit application fee,
I
to be charged forsubsequent reviews due to ft insufficlency of the
fermit appocatio
s.
For DENR use only
SUBMITTAL DATES: Fee Split for multiple permits:
SW $ _._.__.-�
CAMA $
`'
LOS $
,y
i
401 $
Total Fee A
ount $
'
i

WILINGTON INTERNATIONALORT
WILMINGTON, NORTH CAR q LINA
STORMWATER MANAGEMENT i PHASE I
May 2005
PROJECT OVERVIEW
This project represents the initial phase of implemen
Plan prepared for Wilmington International Airport i
includes a portion of Extended Dry Detention Basin'
Stormwater Conveyance Pipeline "A" as depicted in
also includes a lateral pipeline extension connecting
Extended Dry Detention Basin No. 1 is a stormwater
address the water quality and peak flow attenuation re
Carolina Stormwater Rules and the New Hanover Co'
Ordinance. The Basin, in the initial configuration cm
serve up to 150 acres of tributary area, with an avera€
The Basin and all tributary area is located entirely on
expected to expand the Basin and its maximum tribut
development projects tributary to Extended Dry Dete
provide supplemental stormwater quality measures ei
efficiency per the North Carolina Stormwater Rules.
The majority of the earthwork and some outlet struci,
Dry Detention Basin No. 1 is being accomplished by
for the NCDOT Martin Luther King, Junior Parkway
stabilized with topsoil and permanent grasses under t
excavation work is expected to be completed in June
Management — Phase I project contract includes fUrd
configuration of Extended Dry Detention Basin No.
The Stormwater Management — Phase I project
72" pipe intended to convey stormwater from t3
Detention Basin No. I. Permitting activity for
commence shortly.
Land disturbance activities for this project are also
Stormwater Conveyance Pipeline and completion c
No. 1. The total land disturbance associated with t
approximately 12 acres.
Lion of the Stor
October 2004,
o, 1 and a porti
ie Master Plan.
Pipeline "A."
of
impervious co
�rport property
y area. High i
ion Basin No.
ivalent to 3 5 0
e work needed
ieans of a. born
roject. The ex
DOT project:
005. The Stoi
r work to tort
;s over 2,100 :
projects to E;
tributary prof
:ed with insta
.xended Dry
project is est
0
Lwater Master
i he project
a of
The project
i
lity intended to
e North
Management C
is intended to
,erage of 65%1,
Future work is
msity
are required fo
TSS removal
i
h
:or Extended
w excavation `
avation will b'
The borrow
ete the initial
tl
of 48" and ;
ded Dry
Will r
,n of the
action Basin;h
,d at
No new impervious areas are being constructed withl this project, ex ept for gravel
maintenance access roads within and bordering the basin. j
h

r
� /

TALBERT & BRIGHT, INC: r
ENGINEERING & PLANNING' CONSU 'TANTS
FACSIMILE TRANSMITTAL
6}
From:
�2 ! G
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To:
NG��N2
Date:
Company:
Fax No.
Total No.
f pages includi
g cove r. r
TBI Ref. Plo.
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— U 5w A.
Tel No.
�X�2S� ��
Project Name:
Subject:
IF YOU DO NOT RECEIVE THE SPECIFIED NUMBER OF PAGES PLEASE CALL US IMMBDIA
WE WILL ASSUME ALL PAGES WERE TRANSMITTED SATISFACTORILY
LY AND WE wiLL RES
ND THE, MISSING & OCUMIENTS,
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NOTES/COMMENTS:
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/",- yDcJ A&Arlg--
61
The information contained in this facsimile message Is privileged and confldenti,
entity named as recipient. If the reader is not the intended recipient, be hereby
communlcatlon is strictly prohiblted. If you have received this communication in
the original mes,sa a to us at the address below via the U.S. Poetai Service. Thai
ENGINEERING & PLANNING CC
4810 Shelley Drive Wilmington, NC 28405 910.
Cliarlo=e, Nardi Carolina • Wilrniagton, North C
r
( ins
4
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irrrietion intended crily for the use of .the individual or
ed that any disse ination, distribution or copy of this
please notify us immediately by telephone and return
U.
LTANTS
r
350 FAX 910.762.E 81
a • Richmond, vir inia
'r

-WILINUNGTON IN"I" El,,3,.NXf IONAt AIRPORT
'illmington, NC
ENGINEERING `tZEP0kl'
RECEIVED
00-26 M4
DWQ
APPROYED,��10
WWROYOUNA ENVIFIONMDft
EWT COMMISSION
WdM OF WATER QWUTr
-W&4-
e(0`1
Storm-wrater Master P'.e,-i
PREPARED FOR
New Hanover County Ai . ., ort
Wihnir,04:ou, North Carolina
n%-. With:
copera;ti
A `0N`ADMl\,TlSTRXfh-)N
Air . X7
AIP3-37-0084-30
and
NOR H CAROT
"INA DEPAPUKENTOF
TRANSPORTMON DIVISION OF AVIATION

Wilmington International Airport (ILM)
Stormwater Master Plan
Table of Contents
Executivesummary........................................................................................... 1
ReRa L#
I.
Purpose .................................................................................................
3
II.
Site Description ....................................................................................
3
III.
Usting -Drainage Patterns..................................................................
5
IV.
Airport Development and Redevelopment ..........................................
11
V.
North Carolina Stormwater Rules .......................................................
12
VI.
New Hanover County Storm Water Management Ordinance ..............
15
VII.
Wildlife Hazard Considerations...........................................................
15
VIII.
Best Management Practices................................................................
16
DC.
Proposed BMP Design Criteria............................................................
17
X.
Proposed Ston�nwater Management Concepts ...................................
18
XI.
Methodology........................................................................................
23
XII.
Implementation of Stormwater Controls ............................................
24
XIII.
Alternative Solutions and Plan Modification ........................................
25
IFIOU
• Fig. 1- Vicinity Map
• Table 1- Soils
• EX 1.0 - Usting Conditions Overall Map (Half Size Plan)
• PR 1.1- Stormwater Management - Centralized Concept (Half Size Plan)
• PR 1.2. - Stormwater Management - Distributed Concept (Half Size Plan)
• PH 1.1 - Stormwater Management. - Distributed Concept Phasing (Half Size
Plan)
Aooendicea
A. 15A NCAC 02H.1000 NC Stormwater Rules
B. New Hanover County Stormwater Ordinance
C. FAA AC 150/5200-33A, "Hazardous Wildlife Attractions on or Near Airports"
D. USDA Wildlife Services Fetter Report Dated June 4, 2004
E. NCDENR Stormwater BMP Manual (6ccerpts)
F. Cost Opinions
Technical Aooendix (Bound Somra llyl
• Computations
TOC-1

Wilmington International Airport (ILM)
Stormwater Master Plan
Executive Summary
This Stormwater Master Plan has been developed for the Wilmington International
Airport, Wilmington, North Carolina. Preparation of the Plan was requested by the
Wilmington office of the North Carolina Department of Environment and Natural
Resources (NCDENR), pursuant to the North Carolina Stormwater Management
Rules (15A NCAC 021-1.1000). Development of the Plan has been funded by the
Federal Aviation Administration (FAA).
The Stormwater Master Plan is a planning tool for providing stormwater
management infrastructure in support of anticipated development activities on
airport property. Extended dry detention basins and grassed swales are proposed
to address the stormwater quality requirements of the NC Rules for areas of "High
Density" development at the airport. "High Density" development is expected to be
concentrated on the west side of the airport, with an overall density of up to 65%
built -upon surface In that area. The extended dry detention basins will also serve
to address the peak flow attenuation criteria in the New Hanover County Storm
Water Management Ordinance.
New stormwater conveyance pipelines are proposed to address the capacity and
depth limitations of the existing stormwater Infrastructure on the west side of the
airport. The proposed conveyance pipelines and extended dry detention basins will
allow positive drainage of all airport stormwater away from the Wildcat Branch
drainage system, which drains the Heritage Park neighborhood located on the west
side of Blue Clay Road. Heritage Park suffers frequent nuisance flooding and
occasional structural flooding. The tributary area to another marginal drainage
system farther south along Blue Clay Road will be reduced. All diverted stormwater
from these areas will be conveyed to Smith Creek via existing outfalis located on
airport property.
The current overall density of built -upon area on airport property Is approximately
16%, which is well under the 30% upper limit for "Low Density" under the North
Carolina Stormwater Management Rules. `[fie overall built -upon area on the airport
property is expected to remain well below the 30% threshold level for the
Page-1

Wilmington International Airport (ILM)
tormwater Master Plan
foreseeable future. NCDENR officials have suggested a Stormwater Master Plan
permit concept that designates the airport as a low density facility with pockets of
high density development, until such time as the overall built -upon density exceeds
30%.
Wildlife hazard issues have been considered in preparation of the Plan. In addition
to a careful review of FAA Advisory Circular 150/5200-33A, "Hazardous Wildlife
Attractants On or Near Airports," which was revised by FAA during the course of
Plan preparation, the USDA Wildlife Services was consulted to interpret the FAA
criteria In the context of local conditions. Wildlife Services has advised that the
Advisory Circular guidelines are applicable at the Wilmington International Airport
and recommends the use of extended dry detention basins and grassed swales
rather than wet detention basins at the airport. Design criteria for extended dry
detention basins and grassed swales on airport property are proposed, derived
from NCDENR design guides and the requirements of the Wildlife Advisory Circular.
Two stormwater management concepts have been developed for the west side of
the airport. 1--: - "ccnralized" stormwater management concept involves using two
large extended d`y detention facilities to serve the development areas on the west
side of the airport. The "distributed" stormwater management concept involves
using multiple smaller extended dry detention basins throughout the area. The
two concepts represent the probable range in size and number of extended dry
detention basin BMP's which may be implemented in support of high density
developments at the airport.
Cost opinions have been prepared for the two stormwater management concepts.
A phasing plan has been developed for the distributed concept, which
demonstrates the potential for Incremental construction of the proposed
improvements, geared to the pace of development.
The airport has initiated financial planning efforts with respect to implementation of
this Plan. The airport seeks NCDENR concurrence with the stormwater
management concepts presented in this plan.
Page-2

Wilmington Internatiomd Airport (ILM)
Stormwater-Master Plan
L Purpose
This Stormwater Management Plan has been developed for the Wilmington
International Airport on behalf of the New Hanover County Airport Authority. The
Plan provides guidance on stormwater management Infrastructure improvements in
support of development projects at the airport. A key objective of the Plan is to
address the North Carolina Stormwater Management rules (15A NCAC 02H.1000)
administered by the North Carolina Department of Environment and Natural
Resources, Division of Water Quality (NCDENR). A copy of these rules is included in
Appendix A. The Plan also considers the following:
New Hanover County Storm Water Management Ordinance (see Appendix
B).
FAA Advisory Circular 150/5200-33A, H&Vrobw Wildlife At&actai& On or
NearAirportr (see Appendix C).
The practical application of the Plan is to provide a technical framework for
processing future NCDENR stormwater permits for individual development projects
on airport property. Another objective of the Plan is to provide conceptual design
of improvements to the stormwater conveyance infrastructure serving the westerly
portion of airport property.
This Stormwater Master Plan consists of this report, a set of plans depicting
existing conditions and the conceptual design of proposed stormwater
' infrastructure improvements and a technical appendix containing supporting
'I computations. Selected plan sheets have been reproduced at half size and bound
l into this report under the "Figures" tab for ready reference.
g. Site Description
1
The Wilmington International Airport is located in southeasterm North Carolina,
north of Wilmington in an unincorporated area of New Hanover County. Refer to
Page-3

t
Wilmington International Airport (ILM)
Stormwater Master Plan
Figure 1. The airport is owned and operated by the New Hanover County Airport
Authority. Airport property lies within an area bounded by the Martin Luther King
Jr. Parkway, 23'd Street, Blue Clay Road, and North Kerr Avenue. The airport
property encompasses over 1,600 acres. This Plan covers the entire airport
property. Various adjoining parcels sharing common hydrology with airport
property have been included in the planning efforts. Existing conditions and
drainage infrastructure on and surrounding airport property are shown on full size
plan sheets EX1.0 through EX 1.5. Sheet EX1.0 is included at half scale under the
"Figures" tab of this report.
The majority of airport property drains to Smith Creek, a tidal tributary of the
Northeast Cape Fear River. A small area of airport property drains to Wildcat
Branch, another tributary of the Northeast Cape Fear River.
The Wilmington International Airport site has been used for aviation since the
1930's. During World War II, the site was requisitioned by the federal government
for use as an army airfield. Much of the current airport Infrastructure (including
stormwater infrastructure) dates back to World War II era construction.
Soils at the airport include fine sands, silts, and clays which range from well -
drained to poorly drained. Table 1 (included under the 'Figures' tab) lists soil
associations found at the airport.
Existing airport stormwater infrastructure includes a series of extensive closed
(pipe and inlet) drainage systems, open channels, pipe culverts, and two
stormwater management basins. Much of the drainage pipe serving airside (aircraft
operating) areas has been rehabilitated over the past five years. These pipe
systems are generally in good condition and adequately sized.
Tha clmed system serving the "land side" of the airline terminal complex is in
generally good working condition, and adequately sized. By contrast, the system
Page-4
1
1

Wilmington International Airport � ILM
g P )
Stormwater Master Plan
of open channels, culverts, and smaller closed systems which drains the remainder
of the western portion of airport property is generally in poor condition and of
limited capacity. This area is currently sparsely developed and will require
significant stormwater Infrastructure improvements to accommodate future
development.
Two existing stormwater management basins were constructed on the airport
during development of the airline terminal complex in the late 1980's. One is a
small wet basin located near the Runway 6 approach. The tributary area to that
basin is mostly unpaved. The other existing basin, located south of Runway 6-24, is
larger and features a shallow permanent pool. The tributary area to that basin is
moderately developed. Refer to plan sheets EX1.0 and EX1.4.
111. Ilbcisting Drainage Patterns
The airport property has been divided into 15 drainage sub -basins, corresponding
to 15 points at which concentrated stormwater is discharged from the airport
drainage system. These drainage sub -basins and discharge points are depicted on
Plan Sheets EX1.0 through EX1.S. A description of each sub -basin follows:
Sub -Basin 1
Sub -basin 1 is located in the northerly quadrant of the intersection of Airport
Boulevard and North 23 d Street. This small (3.7 acres) sub -basin drains via a 24"
culvert under 23"d Street. Existing ground cover includes roadway pavement and a
large grassy area.
I
Sub -Basin 2
i Sub -basin 2 is located in the southerly quadrant of the intersection of Airport
Boulevard and forth 23ro Street. This small (10.5 acres) sub -basin drains via two
j culverts (18" and 24") under 23ro Street. Usting ground cover includes roadway
pavement and large expanses of grass and woods.
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Sub -Basin 3
Sub -basin 3 encompasses 114 acres extending from the intersection of Gardner
Drive and Trask Drive to a point south of the intersection of Gardner Drive and
Airport Boulevard. Existing ground cover in this sub -basin Includes large areas of
grass, wooded areas and several airport and leasehold buildings and associated
parking areas. Most of the sub -basin drains via shallow open channels to a closed
pipe system constructed during World War H. This closed pipe system drained a
runway and associated taxiways which have since been removed. Airport
Boulevard follows the alignment of the old runway, much of which remains intact
east of the airline terminal complex. Except for a length of 42" diameter pipe
replaced during construction of Airport Boulevard, the pipe system is believed to be
in poor condition. Numerous sink holes along the pipe runs provide evidence of
leaking pipe joints. This condition has been found In many of the old storm
pipelines on the airfield. The existing pipeline, plus an additional shallow 18"
diameter pipeline under Airport Boulevard, is adequately sized to handle the runoff
from the sub -basin in Its current condition, but is not adequate to drain the same
area in a densely developed condition. System Improvements should be
° undertaken in support of any significant development or redevelopment activity in
e
the sub -basin.
The outfall of sub -basin 3 Is an existing open channel, more than 2,000 feet in
length, which passes through a densely wooded area enroute to Smith Creek. The
channel passes through a 36" culvert located adjacent to the airport sewer pump
station.
4
} Sub -Basin 4
Sub -basin 4 comprises most of the land side of the airline terminal complex. The
63 acre sub -basin includes significant amounts of impervious surface (roadways,
parking lots, roofs, pedestrian areas), but also includes large grassy open spaces.
1
The sub -basin Is drained by a large closed pipe system constructed for the terminal
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i complex in the late 1980's. The system is generally of adequate capacity and is
1 generally in good condition, with the exception of a few World War 11 era pipeline
segments Incorporated in the system. The outfall of sub -basin 4 Is an existing
! open channel, more than 1,500 feet in length, which passes through a densely
wooded area enroute to Smith Creek.
e
Sub -Basin 5
Sub -basin 5 comprises 25 acres located between the airline terminal building and
the approach to Runway 6. The sub -basin includes both impervious surfacing and
grassy open space. The sub -basin features a small wet detention basin
constructed In the late 1980's as part of the airline terminal complex. The sub -
basin outfalis through an open channel to Smith Creek.
Sub -Basin 6
Sub -basin 6 comprises 121 acres, including portions of the amine terminal complex
and the west side general aviation area, as well as airfield pavement and grassy
areas adjacent to Runway 6-24. The area is drained by a large closed pipe system
which Is a combination of World War II era pipe segments and newer segments.
Many of the older pipe segments in this system have been rehabilitated over the
last 5 years to address severe joint leakage and consequent subsurface soil
erosion. The system is generally of adequate capacity to serve its tributary area.
Sub -basin 6 drains to an existing wet detention basin before discharging via a twin
48" culvert to an open channel more than 700 feet in length, passing through a
densely wooded area enroute to Smith Creek.
Sub -Basin 7
Sub -basin 7 comprises 68 acres, which includes airfield pavement and grassy areas
adjacent to both runways. The sub -basin Is drained by a closed pipe system which
is of adequate capacity. Many of the older pipe segments In this system have been
f rehabilitated over the last 5 years to address severe joint leakage and consequent
subsurface soil erosion. Sub -basin 6 outlets to an open channel more than 700
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feet in length, passing through a densely wooded area enroute to Smith Creek.
Sub -Basin 8
Sub -basin 8 comprises 120 acres located in the southeasterly quadrant of the
airport. The sub -basin includes the south side general aviation area, the FAA
airport traffic control tower facility and the Army National Guard facility. Sub -basin
8 Includes large areas of impervious surfacing, grassy open space and wooded
areas. Sub -basin 8 is drained by closed pipe systems, swales and culverts, with
several outfalls to the vast forested wetlands along Smith Creek. The sub -basin
has been further subdivided into five smaller areas (8a through 8e), representing
the various outfalis. Sub -basin 8a is drained by a closed pipe system, which Is of
adequate capacity. Many of the older pipe segments in this system have been
rehabilitated over the last 5 years to address severe joint leakage and consequent
subsurface soil erosion.
Sub -Basin 9
Sub -basin 9 comprises 59 acres on the east side of the airport. It Includes airfield
pavement, aircraft hangars and grassy areas. Sub -basin 9 is drained by two closed
pipe systems which are generally of adequate capacity. Many of the older pipe
segments in this system have been rehabilitated over the last 5 years to address
severe joint leakage and consequent subsurface soil erosion. The sub -basin drains
via a 30" culvert under North Kerr Avenue.
Sub -Basin 10
Sub -basin 10 comprises 209 acres on the east side of the airfield. The sub -basin
includes airfield pavement and large areas of grassy open space. The lower
reaches of the sub -basin are wooded. The sub -basin is drained by closed pipe
systems, swales and culverts. A tributary of Smith Creek, sometimes known as
Acorn Branch passes through the sub -basin via triple barrel culverts under ia)dway
B and Runway 6-24. The sub -basin, and Acorn Branch, drain via a triple 72"
culvert under North Kerr Avenue.
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The pipe systems in sub -basin 10 are generally of adequate capacity for existing
conditions. Many of the older pipe segments in these systems have been
rehabilitated over the last: 5 years to address severe joint leakage and consequent
subsurface soil erosion.
Sub -Basin 11
Sub -basin 11 comprises 103 acres located in the northeasterly quadrant of the
airport. The sub -basin is primarily grassy open space, plus asmall area of airfield
pavement. The sub -basin drains via swales to a 42- culvert under North Kerr
Avenue.
Sub -Basin 12
Sub -basin 12 comprises 91 acres located in the central portion of the airfield.
Existing ground cover includes airfield pavement and large areas of grassy open
space. The sub -basin is drained by a closed pipe system, which is generally of
adequate capacity. Many of the older pipe segments in this system have been
rehabilitated over the last 5 years to address severe joint leakage and consequent
subsurface soil erosion. Sub -basin 12 discharges to an off -site channel which flows
to Acorn Branch, upstream of Sub -basin 10.
i
Sub -Basin 13
Sub -basin 13 comprises 207 acres located in the northerly portion of the airfield.
The sub -basin includes airfield pavement, grassy open space, wooded areas and a
developed area between Taxiway A and Trask Drive. The sub -basin Is drained by
closed pipe systems and open channels. Many of the older pipe segments in these
systems have been rehabilitated over the last 5 years to address severe joint
leakage and consequent subsurface soil erosion.
The pipe system which drains the taxiway and runway areas of sub -basin 13 is
j generally of adequate capacity and Is In good condition. The pipe systems which
serve the north ramp and old airline terminal areas in the sub -basin vary in
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condition from good to poor. The configuration of this system is poor. System
Improvements should be undertaken in support of any significant development or
redevelopment activity in the sub -basin. Sub -basin 13 discharges to an off -site
channel which flows to Acorn Branch, upstream of Sub -basin 10.
Sub -Basin 14
Sub -basin 14 comprises 66 acres located in the northwest ouadrant of the airport.
The sub -basin is predominantly forested, with areas of grassy open space. Sub -
basin 14 drains via a 42" culvert under the CSX railroad and Blue Clay Road. This
culvert outlets to Wildcat Branch, a tributary of the Northeast Cape Fear River. The
area immediately downstream of the culvert is a residential area known as Heritage
Park, which is subject to frequent flooding. A study conducted in 2001 indicates
that flow from the airport side of Blue Clay Road does not contribute substantially
to the flooding problem in Heritage Park. The a fisting ground cover and low flow
velocities on the airport land, coupled with a large storage volume available in the
depression on the upstream end of the 4r culvert, result in minimal discharge to
Wildcat Branch. Stormwater from any new development within sub -basin 14
should be directed away from the Wildcat Branch watershed, so as to avoid any
potential increase in flooding in Heritage Park.
Sub -Basin 15
Sub -basin 15 comprises 64 acres located on the west side of the airport. The sub -
basin is largely forested, with the exception of the existing USDA and New Hanover
County facilities located near the intersection of Gardner and Hewlett Drives. Sub -
basin 15 is drained by small closed pipe systems, ditches and culverts. These
systems are generally small and of marginal capacity. The sub -basin outlet is a 30"
culvert under the CSX railroad and Blue Clay Road. 'Downstream of Blue Clay
Road, the discharge passes through an industrial area before passing under North
23ro Street. The capacity of this system is considered marginal. The sub -basin
Includes a 10 acre leasehold parcel upon which the 84 Lumber Company plans to
build a contractor yard served by a rail spur.
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i IV. Airport Development and Redevelopment
Planning for development and redevelopment projects at the Wilmington
International Airport is essentially a continuous process. Airport development plans
evolve over time in response to user and, community needs, priorities and
opportunities. Additionally, the airport anticipates growing demand for airport
business park leasehold space. The following discussion presents a "snap shot" of
near term and long term airport development concepts considered In this
Stormwater Master Plan.
General Aviation
Expansion and enhancement of the general aviation facilities is a significant near
term and continuing long term goal at the airport. New general aviation terminal
building facilities, aircraft hangars, aircraft parking apron space, fuel storage
facilities and automobile parking are needed to accommodate growing demand.
The expansion and enhancement of general aviation facilities is planned on both
the west side of the airport and the southeast side of the airport.
Airline Terminal Complex
The airport has recently completed a major remodeling project at the airline
terminal. Strong growth in airline passenger counts is anticipated. Near term
needs include passenger parking lot expansion and rental car lot expansion. In the
I long term, a second gate concourse and associated apron expansion are planned,
as demand warrants.
Airfield
Near term projects on the airfield include perimeter roadway improvements (safety
and security access inside the airport fence), Runway 6-24 pavement rehabilitation,
general aviation apron pavement rehabilitation and the installation of Instrument
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Landing Systems (ILS) serving both ends of Runway 6-24. Longer term airfield
improvements include additional airfield pavement rehabilitation projects (taxiways
and aprons), taxiway widening/relocation projects and a potential 2,000 foot
extension of Runway 6-24 and its parallel taxiway.
Other Aviation Related Facilities
Other anticipated or potential aviation related airport develoomentlreda elopment
projects include large corporate aviation needs (such as larger air cargo or aircraft
maintenance facilities), relocation of rental car servicing facilities,
1 expansion/improvement of U. S. Customs facilities, and re -use of the old airline
terminal building.
Airpgrt Business Park
The airport is actively marketing airport business park leasehold sites on the west
side of the airport for a variety of potential uses including office, hotel, light
manufacturing, warehousing, wholesale and other compatible uses. A site has
recently been leased to the 84 Lumber Company for a contractor lumber yard.
V. Worth Carolina Stormwater Rules
i
The North Carolina Stormwater Rules are codified at 15A NCAC 021-1.1000 and are
administered by the North Carolina Department of Environment and Natural
Resources, Division of Water Quality (NCDENR). The rules originally went into
effect on January 1, 1988, and were amended in 1995. The rules require a
stormwater permit for any development activity within a coastal county which
requires a CAMA major development permit or a Sedimentation/Erosion Control
Plan (required for land disturbances of one acre or more). Development is defined
as any land disturbing activity which increases the amount of built -upon area (i.e.,
pavement, gravel roads, roof tops) or which otherwise decreases the infiltration of
precipitation into the soil.
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The Wilmington International Airport is located in coastal New Hanover County and
drains to Smith Creek and the Northeast Cape Fear River, Smith Creek is classified
as "C; Sw" (Aquatic Life, Secondary Recreation, Fresh, Swamp Waters) and the
Northeast Cape Fear River is classified as "SC; Sw" (Aquatic Life, Secondary
Recreation, Salt, Swamp Waters). In the absence of classification as "SA" (Market
Shellfishing, Salt Water), "ORW" (Outstanding Resource Waters) or "HQW" (High
Quality Waters), the requirements of 15A NCAC 02H.1005 (3) apply. Under this
paragraph, "Low Density" projects (i.e., projects for which structural stormwater
controls are not required) are defined as developments having a built -upon area of
30 percent or less. Low Density projects must also feature stormwater runoff
transported primarily by vegetated conveyances, a stormwater conveyance system
which does not include a discrete stormwater collection system, and a 30 foot wide
vegetative buffer adjacent to surface waters. "High Density" projects (i.e., projects
for which structural stormwater controls are required) are projects involving more
than 30 percent built -upon area. High density projects require stormwater control
systems which must be wet detention ponds, infiltration systems or "alternative
stormwater management systems," and which must be designed to control runoff
from all surfaces generated by one Inch of rainfall.
Historically, development projects at the Wilmington International Airport have
been permitted under the "Low Density" option, due to the overall built -upon
surface area on airport property, which is well under 30 percent. In May of 2001,
the local office of NCDENR advised the airportin writing that "additional built -upon
area at the Airport cannot be permitted under the Low Density option until a
Master Drainage Plan is submitted to and permitted by this office." The regulatory
basis for stormwater master plan permits is found at 15A NCAC 02H.1003 (h)(3).
Officials from the Wilmington office of NCDENR have provided verbal guidance
regarding NCDENR policy and practice relative to master plan permits. The
foilowing discussion paraphrases that guidance. A facility may receive a master
plan permit under either high density or low density provisions. Facilities with an
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Wilmington International Airport (ILM) �
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overall built -upon area density in excess of the high density threshold would be
required to hold a high density master plan permit. These facilities would be
required to implement high density BMP controls for all development projects
involving an Increase in built -upon area. Facilities with an overall built -upon area
density below the high density threshold would be allowed to hold a low density
1 masher plan permit, even if certain areas within the facility site are characterized as
pockets of high density development. Facilities with a low density master Dlan
permit would be allowed to construct development projects which are consistent
with low density criteria without Implementing high density IMP controls. For
development projects characterized as pockets of high density development at
facilities with a low density master plan, NCDENR would require implementation of
high density BMP controls.
NCDENR officials advise that three criteria are evaluated in making a determination
as to whether a development project will be characterized as a pocket of high
density development. The criteria for high density pockets are as follows:
1. Built -upon surfaces in high density pockets are clustered
(concentrated) together geographically within the facility site.
2. High density pockets are drained by stormwater callecHan systems.
3. Built -upon surfaces in high density pockets do not drain by sheet flow
across vegetated surfaces.
This Stormwater Master Plan is based on overall low density with anticipated
pockets of high density development.
l
The existing runway and ta)away complex on the airfield are considered to be
consistent with low density criteria because the built -upon surfaces are distributed
through the site and the built -upon surfaces drain by sheet flow over large grass
t
areas. The runway and taxiway complex is served by a stormwater collection
system which predates the Stormwater Rules and which collects the runoff
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downstream of the sheet flow areas.
V1. New Hanover County Storm Water Management Ordinance
New Hanover County adopted a Storm Water Management Ordinance on
I September 5, 2000. A copy of the ordinance is included as Appendix B. The
ordinance requires peak flow attenuation for new development in the County such
that peak flow rates for post -development conditions do not exceed peak flow rates
for pre -development conditions for 2-year, 10-year and 25-year storm events. For
redevelopment activities, the ordinance requires peak flow attenuation for a 10-
year event. The design of extended dry detention basins on the airport must
satisfy these requirements.
VIZ. Wildlife Hazard Considerations
Wildlife activity on and in the vicinity of airports presents a serious hazard to
aviation safety. On May 1, 1997, the Federal Aviation Administration (FAA) issued
Advisory Circular No. 150/5200-33, "Hazardous Wildlife Attractants On Or Near
Alrports," (the "Wildlife ACC. A draft revision of this document was Issued by FAA
on January 30, 2004. The revised AC, designated as No. 150/5200-33A, was
issued on July 27, 2004. A copy of the current AC is included in Appendix C.
The Wildlife AC was developed by FAA from a nation-wide perspective. During
development of the scope of work for the Stormwater Master Plan project, the
wildlife hazard issue relative to stormwater BMP design was recognized as a key
issue in development of the Plan. It was considered prudent to review wildlife
concerns from a local, site specific perspective as well as in the nation-wide context
of the Wildlife AC. The United States Department of Agriculture, Wildlife Services,
has provided this local perspective, based on site visits to the airport and
discussions with Talbert & Bright and airport staff. A letter report summarizing the
findings and recommendations of Wildlife Services is included in Appendix D.
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The Wildlife Services report states that the guidance of the Wildlife AC Is applicable
to the Wilmington International Airport. The report strongly advocates avoidance
of wet detention basins and recommends the use of extended dry detention basins
for stormwater management. The report provides further recommendations
relative to the design details for extended dry detention basin and grassed swale
BMP's on the airport.
The Wildlife AC provides guidance on the design of stormwater detention basins on
airports. Specifically, the AC stipulates the use of steep -sided, narrow, linearly
shaped (dry) detention basins with a maximum detention time of 48 hours for the
design storm.
I VUL Best Management Practices
Most large development projects In coastal southeastern North Carolina utilize wet
detention basins as the primary stormwater BMP. Use of wet basins for the
Wilmington International Airport was actively studied during plan preparation,
however due to the wildlife hazard issue, it has been determined that stormwater
management at the Wilmington International Airport should be accomplished
primarily with a of c�iiiciiu u Udiy Uateil"Llon basins of d grassW swales
needed to meet the required 85% pollutant removal efficiency stipulated under
North Carolina stormwater rules. NCDBNR has assigned a removal efficiency of
50% to the extended dry detention BMP and 35% to the grassed swale BMP. The
extended dry detention basins will also serve to meet the peak discharge
attenuation requirements of the New Hanover County Storm Water Management
Ordinance.
Wet detention basins, extended detention wetlands, pocket wetlands, bioretention
i areas, infiltration devices, aria other BMPs which involve a permanent pooi of open
water, water quality draw -down times exceeding 48 hours, and/or artificial wetland
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type conditions will be excluded from consideration at the Wilmington International
Airport. These BMPs are generally expected to create conditions that attract wildlife
species which are hazardous to aviation. In accordance with the Wildlife AC,
creation of these potential attractants of hazardous wildlife must be avoided.
DL Proposed BMP Design Criteria
Design criteria specific to the Wilmington International Airport have been
developed for extended dry detention basins and grass swales. The criteria are
based on the requirements set forth in the North Carolina Stormwater Rules,
guidance in the NCDENR Stormwater BMP Manual (see Appendix E), the
requirements of the New Hanover County Storm Water Management Ordinance
and the requirements of FAA AC 150/5200-33A, "Hazardous Wildlife Attractions on
or Near Airports". The following is a list of -criteria developed using the previously
mentioned documents:
EXtended Dry Basins
1. The basin should be steep -sided, narrow, and linearly -shaped.
2. Capture the runoff from a 1" rainfall and release over a period of 48 hours.
3. Provide a minimum flow length -to -basin width ratio of 3:1
4. Provide side slopes in the range of 3:1 to 4: 1 (horizontal: vertical).
5. Install outlet orrice in an enclosed structure with a sump. Provide a trash
rack on the inlet to the structure. Do not provide an open permanent pool.
y 6. Provide a rip -rap or concrete lined low -flow channel from inlet to outlet with
a minimum depth of one (1) foot.
7. Slope basin bottom at a 2% preferred and 1% minimum grade toward low
flow channel.
8. Provide heavy equipment access for clean -out and maintenance.
9. Provide excess storage in the lower levels of the basin amounting to 20% of
the 1" rainfall event runoff volume.
i 10. Provide for peals flow attenuation above the 1" storm storage, in
i accordance with the New Hanover County Storm Water Management
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Ordinance.
11. Provide for seeding the basin bottom side slopes and berms with com
Bermuda grass or other appropriate mbt. Seed mbcture shall not contain
form of millet, rye grass or other large seed producing grasses.
12. Stabilize the basin within 14 days of construction completion.
13. To the extent possible, position the bottom of the basin above the seasonal
high water table.
14. Provide for safe conveyance of a 100-year storm event.
Grassed Swales
1. Swales will typically be located upstream of extended dry detention basins.
2. Provide a 0.2% minimum to 4.0% maximum longitudinal slope.
3. Provide side slopes no steeper than 3:1 (horizontal: vertical) with 5:1
preferred. The swale cross section should be triangular or parabolic.
4. Swale bottom should be located above the seasonal high water table.
S. Swales should be designed for ready mowing with standard mowing
equipment.
6. Flow velocity should be limited to 2 feet per second for the 2-year design
flow and a non -erosive velocity for the 10-year design flow.
7. An attempt shall be made to provide 100 linear fleet of swale per acre of
drainage area. No less than 50 linear feet of swale per acre shall be
provided.
8. Provide for seeding the Swale with common Bermuda grass or other
appropriate mbc. Seed mixture shall not contain any form of millet, rye
grass or other large seed producing grasses.
9. Stabilize the Swale within 14 days of construction completion.
X. proposed StDrmwater Management Concepts
This plan presents two solutions to stormwater management for the west side of
the VAlmington International Airport. These two solutions include a centralized
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stormwater management concept and a distributed stormwater management
concept. Both concepts will require construction of new stormwater conveyance
pipelines tm serve the west side of the airport property. Discussion of each concept
is included in the following sections.
The extended dry detention basin and stormwater conveyance pipeline designs
included and depicted in this Plan have been developed to the conceptual design
level only. Final design, supported by topographic survey, wetlands delineation
and subsurface exploration efforts, must be undertaken for all facilities prior to
construction.
The extended dry detention basin designs have been developed with an assumed
development density of 659E bulb upon area for extended dry detention basin No.
1 and for the distributed concept example basin. An assumed density of 60% was
used In the design of extended dry detention basin No. 2.
Centralized Stormwater Management.Cgriceot
The Centralized Stormwater Management Concept involves stormwater conveyance
to centralized stormwater detention facilities for treatment and control of peak
flows. This concert is depicted an Flaure/Plan Sheet PRU. In the centralized
concept, two large extended dry detention basins would be constructed to serve
the future built -upon areas on the west side of the airport.
Extended dry detention basin No. 1 would be located south of Airport Boulevard
and is sized to capture and treat runoff from approximately 328 acres. The area
draining to this basin Includes the airport business park
development/redevelopment, the airline terminal facility expansion and the GA
apron expansion/redevelopment area. Conveyance of stormwater from the
individual project sites will be through a new stormwater conveyance system
included as part of this master plan. Stormwater will discharge from basin No. 1
through four outlet control structures located at existing airport outfall points.
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Qutfall structures are sized to limit flow into downstream channels to
predevelopment peaks to minimize any erosion or degradation of the existing
channels. Three of the outfall points flow through open channels to Smith Creek.
The other outfall point will be through an existing culvert: under 2.V Street.
Extended dry detention basin No. 2 would be located west of Runway 17-35, with a
portion of the basin located between the Runwav and Taxtwav "A" and the second
portion of the basin located north of Taxiway W. These two basin areas will be
interconnected with a 60" pipe. Extended dry detention basin No. 2 Is .sized to
capture and treat runoff from approximately 164 acres and will be used to provide
treatment for stormwater runoff from the General Aviation facilities expansion area
and other aviation related or commercial development along Trask Drive, north of
the existing General Aviation area. Stormwater will discharge from basin No. 2
through three outlet control structures connected to existing stormwater pipelines.
Concrete or rip -rap low flow channels will be constructed in the bottom of both
basin No. 1 and No. 2 to help maintain a dry basin bottom as required by the
Wildlife AC and to'facllitate maintenance. Both extended dry detention basins are
designed to treat the runoff from a 1" rainfall event, along with attenuating the
peak flow leaving the airport property for 2-year, 10-year and 25-year storm
events. The basins will also be able to safely convey a 100-year storm event.
Computations are included in the technical appendix.
Distributed Stormwater Management Conceet
The Distributed Stormwater Management Concept is based on the idea that
stormwater is detained and treated locally at each project site and then conveyed
off airport property. This concept is depicted on Figure/Plan Sheet PR1.2. The
distributed concept will be used only for the approximately 328 acres of land which
drain to extended dry detention basin No. 1 in the centralized concept. Anticipated
I development in this area Includes airport business park development, airline
terminal facility expansion and general aviation facility expansion. The 164 acres
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of land discussed in the centralized stormwater management concept that drains to
extended dry detention basin No, 2 will also drain to this basin in the distributed
concept.
One example extended dry detention basin design has been completed for the
distributed concept. The example basin would serve the general aviation, long
term parking and rental car parking expansion projects. Computations are included
In the technical appendix. Individual extended dry detention basins have been
sized approximately for each development area, using a ratio of basin area to
tributary area developed from the example basin design. An outlet control
structure will be constructed in each basin to control flow into the stormwater
conveyance system included as part of this master plan. The extended dry
detention basins sized for the master plan are based on the idea that each
development area will have one basin. The actual number, location and size of the
distributed basins will depend on the nature and scope of individual airport and
tenant projects as they arise.
Concrete or rip -rap lined low flow channels will be constructed in the bottom of all
basins to help maintain a dry basin bottom as required by the Wildlife AC and to
facilitate maintenance. All dry detention basins will be designed to treat the runoff
from a 1" rainfall event, along with attenuation of the peak flow leaving the airport
property for the 2-year, 10-year and 25year storm events. The basins will also be
able to safely convey the 100 year storm event.
Stormwater nv nce Pipglin
Both the centralized concept and the distributed concept will require construction
of stormwater conveyance pipelines to collect and convey runoff from the 328 acre
development area tributary to extended dry detention basin No. 1. The
conveyance system consists of three pipelines (A, B and C) located within the
! Business Park Development area. Conveyance system A will be used to carry
runoff from the CP. terminal expa^sloe area, airline terminal expansion area and
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Wilmington International Airport (ILM)
tormwater Master Plan
the portion of the Business Park Development area north of Hewlett Drive and east
of Gardner Drive. Conveyance system B will be used to carry runoff from the
Business Park Development area north of Airport Boulevard, east of Gardner Drive
and south of Hewlett Drive. Conveyance system C will be used to carry runoff from
the Business Park Development area north of Airport Boulevard, west of Gardner
Drive and extending north to drain the existing forested depression to be used as a
detention basin located adjacent to Blue Clay Road.
The size of the conveyance system pipelines varies based on the management
concept. For both concepts, the conveyance system is sized to convey 25-year
storm flows with minimal surcharge (hydraulic grade line no more than 2 feet
above the pipe crown). For the centralized concept, the pipelines will be larger
than for the distributed concept since they will be required to convey runoff directly
from the development area without any peak flow attenuation. The pipelines will
outlet into extended dry detention basin No. 1 which will treat and attenuate the
flow prior to leaving the Airport.
For the distributed concept, the pipelines will be smaller than for the centralized
concept since they will convey the attenuated stormwater flows from the
distributed basins. The pipelines will outlet into a distribution system that will
distribute the runoff to existing Airport outfall pipes and channels.
Cost Opinions for Stormwater Management Concepts
Cost opinions have been developed for the stormwater management concepts
developed for the west side of the Airport. These cost opinions are intended solely
as budgetary planning tools. More detailed cost opinions should be developed for
individual system components during the project design development process to
verify budgetary considerations.
The total cost opinion for the centralized concept, in 2004 dollars, is $9.7 Million.
The total cost opinion for the distributed concept, In 2004 dollars, is $10.7 Million.
Page-22

Wilmington International Airport (ILM)
ttrrmwater Master Plan
Cost opinion worksheets are presented in Appendix "P.
Construction of infrastructure improvements for both stormwater management
concepts can be phased to spread Implementation costs over a period of time as
development progresses. The distributed concept can be more readily phased than
the centralized concept. A phasing plan (plan sheet PH1.1) has been prepared for
the distributed concept. The plan presents four phases of construction. Costs for
each phase have been divided between Airport costs and tenant costs. Phase one
would include expansion of the existing airline terminal parking lot and expansion
of the existing general aviation area. The work would include construction of an
extended dry detention basin for each development area which would initially
outlet into the existing drainage conveyance system (and ultimately into the new
conveyance system). The cost of the basins would be an Airport cost. Phase one
would also include development of two business park sites directly south of Airport
Boulevard which would also require extended dry detention basins %or each
development area. Construction of these stormwater basins would be a tenant
cost. The distributed concept phasing then progresses to the north in three
additional Increments.
X1. Methodology
The SCS unit hydrograph method has been used for project hydrology,
implemented using PondPack software from Haestad Methods, Inc. CN and time of
concentration data were developed using SCS TR 55 methods. The hydrologic soil
groups for the various soil units on the airport were taken from the Appendix A
listing of TR-55. The SCS soil map for New Hanover County was used to identify
soil units. For soils with multiple hydrologic soil groups, the lowest (most well
drained) group was used. The SCS type III 24-hour rainfall distribution was used.
Rainfall depths were taken from the New Hanover County Storm Water Design
Manual. FHWA pipe culvert hydraulic data and standard weir and orifice hydraulic
methods were employed. Pipeline hydraulic grade lines were computed using
Page-23

Wilmington In terns tional Ah port (ILM)
tormwuter Muster Pun
I StormCad software, also from Haestad Methods, Inc.
For extended dry detention basin design, the runoff volume for the one inch rainfall
event was estimated using the Schueler equation:
Rv=.009(I)+.05
The required 20% sediment storage was computed based on this volume, and was
assumed to occupy the lowest level of the basin on either side of the low flow
channel. For the PondPack model, this volume was subtracted from the stage -
storage curve. The SCS method yields very low runoff volumes for a one -Inch 24-
hour rainfall, due to the standard initial abstraction. Therefore, a higher 24-hour
rainfall was input into the PondPack model such that the model would generate a
runoff hydrograph with a volume equal to that predicted by the Schueler equation.
This hydrograph was then routed through the basin in order to size the dewatering
device to drain the runoff from the equivalent 1" design storm in approximately 48-
hours (this detention time is consistent with the minimum required to meet
NCDENR criteria and the maximum consistent with the WiIdift AC). The drain time
was taken as the difference in time from the start of outflow to the end of outflow
in the basin routing outflow hydrograph. Reservoir routings were completed for 2-
year, 10-year, 25-year and 100-year rainfall events as well, In order to size the
peak attenuation storage and outlet structures, confirm pre- versus post -
development peak discharge control, and confirm the safe passage of a 100-year
event.
Xii. Implementation of 5tormwater Controls
Stormwater controls will be implemented on an incremental basis as high density
development involving a net increase in built -upon area occurs. It Is not the intent
I of the Airport Authority to implement BMrs to serve areas that are already
{ developed as of the date of this Plan, nor for redevelopment of such areas (to the
Page-24
s
I

i
Wilmington International Airport (ILM)
Storrnwater Master Plan
extent that such redevelopment does not result in a net increase in impervious
surfacing).
XIII. Alternative Solutions and Plan Modification
This Plan has been developed based on analysis, study and consultation with
airport staff. It presents workable solutions to the long term storm water
management needs of the airport. The plan is conceptual in nature.
Implementation of the Plan will depend in large part on the exact nature,
magnitude and sequence of development projects which move forward, and on
funding resources which become available for construction of stormwater
improvements. Nothing in this plan is intended to limit or restrict the airport or its
current or prospective tenants with respect to pursuing alternative or modified
stormwater management solutions in various locations.
a
i
Page-25

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TALBBRT$ BRIGHT Wilmington internsfin l Airport Figure
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OM AUGUST 2M6 Dlaem . IMM

x"; °4"':'��%gPar•Cs`r�� � �,tS', ni � !�'^ �'r,:,..
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mbol Name Grow
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ep
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Stallings
C
Wr
WrIahtsbom
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*- First soil group denotes drained condemn
while the second denotes undralned condition.
Sourms:
New Hanover County Sol Map
Exhibit A, SCS TM, 2nd Ed, 6M

INTER.'."_,'M�N'.TAL AIRPOR7
Wilmington, NC
IZN�JINEERING REP0j-<-f
RECEIVED
tits' 29 2M
DWQ
APPROVED
WMH CAROUNA ENVIAONM�
MANAGEMENT COMMISS1014
DMSION CF WATER ouwy..�
V— Z X,
02"
1-0
Stormwater Nlaster Plan
PRE i ARED FOR.
Nrew Hanover #Clounly,Ab- oint AuLlority
�p v
Wilmington, NNorth Carolina
in Cooperation
FEDERAL AVt'rAT"1ON AyDMVSTt5TRxf ION
Alt' 3-37-0084-30
and
':?.'1 T Y -,,�T
"- A \N"1PORTA-
LR_S1INATION f) 7

Wilmington International Airport (ILA)
Stormwater '• Aster Plan
Table air a.ontents
Qw2axw SumMM.
R -_i
I.
Purpose.................................................................................................
3
A.
Site Description....................................................................................
3
III.
Existing Drainage Patterns..................................................................
5
IV.
Airport Development and Redevelopment ..........................................
11
V.
North Carolina Stormwater Rules .......................................................
12
VI.
New Hanover County Storm Water Management Ordinance ..............
15
VII.
Wildlife Hazard Considerations...........................................................
15
VM.
Best Management Practices................................................................
16
W.
Proposed BMP Design! Criteria ............................................................
17
X.
Proposed Stormwater Management Concepts ...................................
18
XI.
Methodology........................................................................................
23
)M.
Implementation of Stormwater Controls ............................................
24
M.
Alternative Solutions and Plan Modification ........................................
25
• Fig. 1- Vicinity Map
■ Table 1- Soils
■ EX 1.0 - Existing Conditions Overall Map (Half Size Plan)
• PR 1.1 Stormwater Management - Centralized Concept (Half Size Plan)
• PR 1.2 - Stonmwvater Management - Distributed Concept (Half Size Plan)
•= PH 1.1 - Stormwater Management, - Dlsiriributed Conch Phasing (Half Size
Plan)
AWenf
A. 15A NCAC 021-1.1000 NC Stormwater Rules
B. New Hanover County 9bormwater Ordinance
C. FAA AC 150/5200-33A, "Hazardous Wildlife Attractions on or Near Airports"
D. USDA Wildlife Services UtW Report Dated June 4, 2004
E. NCDENR Stemwater BMP Manual (Excerpts)
P. Cost Opinions
Tectii ►W9endixMound Svgl
■ Comguions
TOC-I

0
Wilmington International A'rport (ILM)
Stormwatcr Plaster Plan
Ekwu b-'-ve Suoimary
This Stormwater Master Man has been developed for the Wilmington Intemational
Airport, Wilmington, North Carolina. Preparation of the Plan was requested by the
Wilmington office of the North Carolina Department of Environment and Natural
Resources (NCDENR), pursuant to the North Carolina Storrriwatea Management
Rules (15A NCAC 021.1.1004). Development of the Plan has been funded by the
Federal Aviation Administration (FAA).
The StOnnWater Master Plan is a planning tool for providing stormwater
management infrastructure in support of anticipated development activities on
airport property. 6ctended dry detention basins and grassed swales are proposed
to address the stormwater quality requirements of the NC Rules for areas of %High
DeW development at the airport "High Denim` development is expected to be
concentrated on the west side of the airport, with an overall density of up to 65%
built -upon surface in that area. The extended dry detention basins will also serve
to address the peak flow attenuation utteda in the New Hanover County Storm
Water Management Ordinance.
New stormwater conveyance pipelines are proposed to address the capacity and
r
depth limitations of the existing stormwater tyre on the wet side of the
airport. 'The wed conveyance pipelines and extended 'dry deterition basins will
allow positive drainage of all airport stormwater away from the Wildcat Branch
drainage system, which drains the Heritage Park neighborhod located on the west
side of Blue aay Road. heritage Park sums frequent nuisance flooding and
oaional structural flooding. The tributary area to another marginal drainage
system farther south along Blue Clay Road will be reduced. All diverted stormwater
from these areas will be conveyed to Smith Creek via existing outfalls located on
airport property.
The current overall density of built -upon area on airport property is approximately
16%, which is well under the 30% upper Urnit for "Low Density" under the North
Carolina Stormwater Management Rules. The overall built -upon area on the airport
property is expected to remain well below the 30% threshold level for the
Page-1

Wilmington International Airport (ILM)
tormwater Master Plan
foreseeable future. NCDENR officials have suggested a Storm oter baste
permit concept that designates the airport as a low dew facility M� pr_
high density development, until such time as the overall built -upon density exceeds
30%.
Wildlife hazard Issues have been considered in preparation of the Plan. In addition
to a careful review of FAA Advisory Circular 150j5200-33A, "Hazardous Wildlife
Attractants On or Near Airports," which was revised by FAA during the course of
Plan- preparation, the USDA Wildlife Services was consulted to interpret the FAA
criteria in the context of local conditions. NAldlife Services has advised that the
Advisory ©ocular guidelines are applicable at the VVilmtngton international Airport
and recommends the use of extended dry detention basins and grassed swales
rather than wet detention basins at the airport. Design criteria for extended dry
detention basins and grassed swales on airport property are prop,
foam NCDENR design guides and the requirements of the Wildlife Advisory Circular.
} Two stnrmwater management concepts have been developed for the west side of
the airport. Thee "centralized" stormwater management concept involves using two
large extended dry detention fadirdes tu buve the development areas on the west
side of the airport. The "distributed" stormwater management concept Involves
using multiple smaller wed dry detention basins throughout the area. The
two concepts represent the probable rare in size and number of extended dry
detention basin BMP's which may be implemented in support of high derialy
develop!r!ents at the airport.
Cost opinions have been prepared for the two stormwater management concepts.
A phasing plan has been developed for the distributed concept which
der aces the potential for Incremental construction of the proposed
impra,mments, gears to the pace of development.
The airport has initiated financial planning efforts with respect to Implementation of
this Man. The airport seeks NCDENR concurrence Wt. the stormwater
management concepts presented to this plan.
9
P%�nP-2

0
Wilmington International Airport (ILM)
SCo ►ti? z� ter i-aster Plan
1. purpose
This Stormwater Management Plan has been developed for the Wilmington
International Airport on behalf of the New Hanover County Airport Authority. The
Plan provides guidance on stormwater management intiastructuure improvements in
support of development projects at the airport. A key objective of the Plan Is to
address the North Carolina St ornwater Management rules (15A NC.AC 02H.1000)
administered by the North Carolina Department of Environment and Natural
Resources, Division of Wager Quality (NCDENR). A copy of these rules is included in
Appendix A. The Plan also considers the fvilowinga
New Hanover County Storm Water Management ordinance (see Appendix
B).
FAA Advisory Circular 150/5200-33A, f awdot s Mffe Affiaclan& On or
NearAhpm&(see Appendix C).
The practical application of the Man is to provide a technical framework for
processing future NCDENR stormwater permits for individual development projects
on airport property. Another' objective of the Plan Is to provide conceptual design
of improves to the stormwater conveyance infrastructure serAng the westerly
portion of airport property.
This Stormwater Master Plan consists of this report, a set of plans depicong
existing conditions and the conceptual design of proposed stormwater
Infrastructure improvements and a technical appendix containing supporting
computations. Selected Plan sheets have been reproduced at half size and bound
into this report under the "Fguresr tab for ready reference.
I. Site le.—::pt fort
The Wilmington International Airport is located in southeastern North Carolina,
north of Wilmington in an unincorporated area of New Hanover County. Refer to
Page-3

Wilmington international Airport (ILM)
Figure 1. The airport is owned and operated by the New Hanover County Airport
Authority. Airport property lies within an area bounded by the Martin Luther ling
3r. ParkwW, 2V Street due Ciay Road, and North Kerr Avenue. The airport
property encompasses over 1,600 acres. This Plan covers the entire airport
property. Various adjoining parcels sharing common hydrology with airport
property have been included in the planning efforts. 6dsting conditions and
drainage infrastructure on and surrounding airport property are shown on Full size
plan streets EX1.0 through IX 1.5. Sheet DC1.0 is included at half scale under the
"Figures" tab of this report.
The majOft of airport property drains to Smith Cm&, a tidal tributary of the
Northeast Cape Fear River. A shall area of airport property drains to Wildcat
Brand, another tributary of the Northeast Cape Fear River.
The Wilmington lnternatiaral Airport site has been used for aviation since the
193(Ys. During Wand War B, the site was requisitioned by the federal government
for use as an army airfdd. Much of the current airport Infrastructure Cinduding
stormwater infrastructure) dates back to World War U era construction.
Soils at the airport include fine sands, siltsl and days which range from well -
drained to poorly drained. Table 1 (Included under the "Figures" tab) lists soil
associations found at the airport.
Existing airport stormwater infrastructure includes a series of eve dosed
(pipe and inlet) drainage systems, open channels, pipe ate, and two
stormwater management basins. Much of the drainage pipe serving airside (aircraft
aperabng) arm has been rehabilitated over the past five years. These pipe
systems are generally in good condition and adequately sized.
The dosed system serving the "'land side" of the airline terminal comic is in
generally good worldng condition, and adequately sized. By contrast, the system
Page-4

Wilmington International Airport (ILM)
S tern arer I;-lus -er Plar
of open channels, culverts, and small dosed systems which drains the remainder
Of the western portion of aimolt property is generally in r,*or aonditian and
limited capacity. This area is currently sparsely developed and will require
significant stormwater lidi r cture improvements to accommodate future
development
Two existing stormwater management basins were constructed on the airport
during development of the airline terminal complex in the late 19WS. One is a
small wet basin located near the Runway 6 approach. The tributary area to that
basin is mostly unpaved. The odd existing basin, located south of Runway 6-24, is
larger and features a shallow permanent pool. The tributary area to that basin is
moderately developed. Refer to plan sheets EX1.0 and EX1.4.
i =, 4 7 ,
The airport Property has been divided into 15 drainage sub -basins, corresponding
to 15 Points at which conaenirated stormwat er is dWorged from the airport
drainage system. These drainage sub -basins and discharge pants are depicted on
Plan Sheets EX1.0 through M.S. A description of each sub -basin follows:
Sub -Basin 1
Sub -basin 1 is located In the r1y quadrant of the intersection of Airport
Soulerard and North 2P Sbeet. This small (3.7 acres) sub -basin drains via a 24'
culvert under 2- d Street. Existing ground cover includes roadway Pavement and a
large grassy area.
Sub -Basin 2
Sub -basin 2 Is located in the southerly quadrant of the intersection of Airport
Boulevard and North 2Yd Street This small (10.5 awes) sub -basin drains via two
culverts (Ir and 24") under 23' Street UsUng ground cover includes roadway
pavement and large expenses of grass and ;goods.
Page-5

Wilmington International Airport (ILM)
5 to-r? water 2M-aster P;aT1
Sub -Basin 3
Sub -basin 3 encompasses 114 awes extending from +fie intersection. of Gardner
Drive and Trask Drive to a paint south of the intersection of Gardner Drive and
A:; port Boulevard. 6dsting ground comer in this sub -basin includes large areas of
grass, wooded areas and several airport and leasehold buildings and associated
parking areas. Most of the sub -basin drains via shallow open channels to a dosed
pipe system constructed during World War H. This closed pipe system drained a
runway and associated taxiways which have since been removed. Airport
Boulevard fbikrws the alignment of the old runway, much of which remains intact
east of the airline terminal complex. Except for a length of 4r diameter pipe
replaced during construction of Airport Boulevard, the pipe Sih is believed to be
in poor condition. Numerous sink holes along the pipe runs provide evidence of
leaking pipe joints. Tb+.is condition has been found in many of the old stain
pipelines on the airfield. The existing pipeline, plus an additional shallow 18"
diameter pipeline under Airport Boulevard, is adequately sized to handle the runoff
from the sub -basin in its current coriclition, but is not adequate to drain the same
area in a densely developed condition. Systun Improvements should be
undertaken in support of any significant development or redevelopment activity in
the sub -basin.
The outfall of sub -basin 3 is an existing open channel, more than 2,000 feet in
length, which passes through a densely wooded area enroute to Smith Creek. The
channel passes through a 3V culvert located adjacent W the airport sewer pump
station.
Sub -Basin 4
Sub -basin 4 comprises most of the land side of the airline termini complex. The
63 acre sub -basin includes significant amounts of impervious surface (roadways,
parking lots, roofs, pedestrian areas), but also Induces large grassy open spaces.
The sub -basin is drained by a large dosed pipe system constructed fbr the terminal

Wilmington International Airport (IL I)
Storrrwarer 3jfastrr Plan
complex in the late 19ffs. The system is generally of adequate capacity and is
generally In good condition, with the emption of a revs World War H era pipeline
segments incorporated In the system. The outfell of sub -basin 4 is an existing
open channel, more than 1,500 feet in length, which passes through a densely
. �.
Sub -Basin 5
Sub -basin 5 comprises 25 acres located between the airline terminal building and
the approach to Runway 6. The sub -basin includes bath Impervious surfacing and
grassy open space. The sub -basin features a small wet detention basin
constructed In the late 19Ws as part of the airline terminal complex. The sub -
basin outfalls through an open channel to Smith Creek.
Sub -Basin 6
Sub -basin 6 comprises 121 acres, inducing portions of the airi€ne terminal complex
and the west side general aAation area, as well as airfield pavement and gray
areas adjacent to Runway 6-24. The area is drained by a large closed pipe system
which is a combination of World War- II era pipe segments and newer segments.
Many of the alder pipe segments in this system have been rehabilitated over the
last 5 years to address severe joint leakage and consequent subsurface soil
erosion. The system is generally of adequate rapacity to serve its tributary area.
Sub -basin 6 drains to an testing wet detention basin before discharging via a grin
48" culvert to an open channel more than 700 feet in length, passing through a
densely wooded area enroute to Smith Creek.
Sub -Basin 7
Sub -basin 7 comprises 68 acres, which includes airfield pavement and grassy areas
adjacent to both runways. The sub -basin is drained by a dosed pipe system which
Is of adequate capacity. Many of the older pipe segment in this system have been
rehabilitated over the last 5 years to address severe ,joint leakage and consequent
subsurface soil erosion. Sub -basin 6 outlets to an open channel more than 7000
Page-7

Wilmington International Airport (ILM) (1411
feet in length, passing through a densely wooded area enmute to Smith Creek.
Sub -basin 8 comprises 120 acres located in the southeasterly quadrant of the
airport. The sub -basin includes the south side general aviation area, the FAA
airport baf is control tower facility and the Army National Guard facility. Sub -basin
8 includes large areas of impervious surfacing, grassy open space and wooded
areas. Sub -basin 8 is drained by closed pipe systems, swales and culverts, with
several oudWls to the vast forested wetlands along Smith (reek. The sub -basin
has been further subdivided into five smaller areas (8a through 8e), reng
the various outlalls. Sub -basin 8a is drained by a dosed ripe system, which is of
adequate capacity. Puny of the older pipe segments in this system have been
rehabilitated over the last 5 years to address severe joint leakage and consequent
subsurface soil erosion.
Sum
Sub -basin 9 comprises 59 acres on the east side of the airport. It includes airfield
pavemeryt� aircraft hangars and grassy areas. Sid -bash 9 Is drained by two dosed
pipe systems which are generally of adequate capacity. Many of the older pipe
segments in this system have been rehabilitated over the last 5 years to address
severe joint leakage and consequent subsurface sal erosion. The sub -basin drains
Via a 3T culvert under North Kerr Avenue,
Sub -Basin 10
Sub -basin 10 comprises 209 acres one the east side of the airfield. The sub -basin
includes airfield pavement and large areas of grassy open space. The lower
reaches of the sub -basin are wooded. ` be sub -basin is drained by dosed pipe
systems, swales and culverts. A tributary of Smith Cnmely sometimes Known as
Acorn Branch, passes through the sub -basin via triple. band culverts under Tadway
B and Runway 5-24. The sub -basin, and Acorn Branch, drain via a triple 72"
culvert under Na;th Kerr Avenue.

Wilmington International Ahport (ILM)
StGMI : 'ater MCIS"V Plan
The pipe systems in sub -basin 10 are generally of adequate capa ft for existing
conditiorns. Many of the older pipe segments in these systems ham been
rehabilitated over the last 5 years to address severe joint leakage and consequent
surface soil erosion.
Sub -Basin 11
Sub -basin 11 comprises 103 acres located in the northerly quadrant of the
airport. The sub -basin is primarily grassy open space, plus a small area of airfield
pavement. The sub -bar n drains Via swales to a 42' culvert under North Kw
Avenue.
�
Sub -basin 12 comprises 91 acres located In the central portion of the airfield.
Ding ground cover includes airfield pavement and large anus of grassy open
space. The sub -basin is drained by a closed pipe system, which is generally of
adequate capacity. Many of the older pipe segments in this system have been
rehabilitated over the last S years to address severe joint leakage and consequent
subsurface soil erosion. Sub -basin 12 dischargess to an off -site channel which flows
to Acorn Branch, upstream of Sub -basin 10.
Sub -Basin 13
Sub -basin 13 comprises 207 acres located in the northerly portion. of the airfield.
The sub -basin includes airfield pawr=nent, grassy open space, wooded areas and a
developed area between Taxwvay A and Trask Drive. The sub -basin is drained by
dosed pipe systems and open channels. Many of the older pipe segments in these
systems have been rehabilitated over tyre last S years to address severe joint
leakage and consequent subsurface soli erosion.
The pipe system which drains the twdway and runway areas of sub -basin 13 is
generally of adequate capacity and is in goad condition. The pipe systems which
serene the notth vamp and old airline tertninal areas in the sub -bay vary in

Wilmington International Airport (M ) .
7rc. 777a417 Tact 77er 7 s-77
condition from good to poor. The configuration of this system is poor. System
improvements should be undertaken in support of any significant development or
redevelopment activity in the sub -basin. Sub -basin 13 discimrges to an off -site
channel which flows to Acorn Branch, upstream of Sub -basin 10.
Sub -Basin 14
Sub -basin 14 comprises 66 acres located in the nordwvest quadrant of the airport.
The sub -basin is predominantly forested, with areas of grassy open space. Sub -
basin 14 drains via a 42w cuhrert under the CSX railroad and Blue Clay Road. This
culvert outlets to Wildcat Branch, a tributary of the Nortiv3ast Cape Fear River. The
area immediately downstream of the culvert is a residential area known as Heritage
Paris, which is subject to frequent flooding. A study conduces in 2001 indicates
that flow from the airport side of Blue Clay Road does not contribute substartally
to the flooding problem in Heritage Park. The eidsting ground cover and low flow
velocities on the airport land, coupled with a large storage volume available in the
depression on the upstream end of the 4r culvert; result in minimal discharge to
Wildcat Branch. Storrrwvater from any, new development within sub -Sin 14
should be directed away from the Wildcat Branch watershed, so as to avoid any
potential increase in flooding in Heritage Park.
Sub -basin 15 comprises 64 acres located on the west side of the airport. the sub -
basin is largely forested, with the exception of the existing USDA and New Hanover
County facilities located near the intersection of Gardner and Hewlett Drives. Sub -
basin 15 is gained by small closed pipe systems, ditches and culverts. These
systems are generally small and of marginal capacity. The sub -basin outlet is a 3W
culvert under the CSX railroad and Blue Clay Road. 'Downstream of Blue Clay
Road, the discharge passes through an industrial area before passing under North
23"° Street. The capacity of this system is considered marginal. The sub -basin
i~iaciudes a 10 acre leasehold parcel upon which the 84 Lumber Company plans to
build a contractor yard served by a rail spur.
Page-10

Wilmington International A'Irp ort (ILM) ��
ito-rr►,:Yatep �Atter F aC�s',
IV..Airu;ort Develo mmd and Re €evellopmenrt
Planning for development and redevelopment projects at the wilmington
International Airport is essentially a continuous process. Airport development plants
evolve over time in response to user arid. community needs, priorities and
opportunities. Addlbonally, the airport anticipates growing demand for airport
business park leasehold space. The following discussion presents a `ksnap shot" of
near berm and tong germ airport development concepts considered in this
Stormwater Master Plan.
General Aviation
Expansion and enhancement of the general aviation facilities is a significant near
germ and continuing long term goal at the airport New general aviation terminal
building facilities, aircraft hangars, aircraft parking apron space, fuel storage
Wities and automobile parldng are needed to accommodate growing demand.
The expansion and enhancement of general aviation facilities Is planned on both
the west side of the airport and the soudteast side of the airport.
Airline Teri
The airport has recently completed a major remodeling project at the airline
terminal. Strong gr . in airline passenger counts is anticipated. Near term
needs include passenger paridng lot expansion and rental car lot expansion. In the
long term, a second gate concourse and associates apron expansion are planned,
as demand warrants.
Airfield
Near term projects on the airfield include perimeter roadway imp (saf ty
and security access inside the airport fence), Runway 6-24 pavement rehabilitation,
general aviation apron pavement rehabilitation and the installation of Instrument
Page-11

Wilmington International Airport (ILM)
Stormwater Master Ma
Landing Systems (Its) serving bath ends of Runway 6-24. Longer term airfield
improvements include additional airfield pavement rehabllit,Rlkim— pmj (te
and aprons), t wdway wideningtrelocation projects and a potential 2,000 foot
eDdension of Runway 6-24 and its parallel ta)dvvray.
Other Aviation Related Facilities
Other anticipated or potential aviation related airport development/redevelopment
projects include large corporate aviation needs (such as larger air cargo or aircraft
maintenance facilities), relocation of rental car servicing facilities,
expandon/improvement of U. S. Customs facilities, and re -use of the old airline
terminal building.
The airport is actively marketing airport business park leasehold sites on the west
side of the airport fnr a variety of potential uses including office, hots, light
manufacturing, warehousing, wholesale and other compatible uses. A site has
recently been leased to the 84 Lumber Company for a contractor lumber yard.
V. North Carolina der Rules
I
The North Carolina Stormwater Rules are codified at 15A NCAC 02H.1000 and are
`. administered b`i the North Carolina Department of Environment and Natural
Resources, Division of 'Water Quaiity (NCDENR). The rules originally went into
effect on January 1, 1988, and were amended in 1995. The rules require a
stormwater permit for any development activity within a coastal county which
requires a CAMA major development permit or a imentation/Erosion Control
Plan (required for land disturbances of one acre or more). Development is defined
as any land disturbing activity which increases the amount of built -upon area (i.e.,
pavement, gravel roads, roof hops) or which otherwilse deavases the infiltration of
precipitation Into the soil.
Page-12

Wilmington International Abport (ILM)
Stormwatrr 7-7-7 aster I'.an
The Wilmington International Airport is located in coastal New Hanover County and
drains to Smith Creek and the Northeast rape Fear Rnw. Smith Creek is classffiled
as -C; Sw" (Aquatic Life, Secondary Recreation, Fresh, Swamp Waters) and the
Nortfieasr Cape Fear Rimer is classified as "SC; Sw" (Aquatic Life, Secondary
Recreation, Salk, Swamp Waters). In the absence of cliassificatIon as "SA" (Marker
Shelifishing, Salt Water), "ORW (Outstanding Resource Waters) or "HQW" (High
Quality Waters), the requirements of 15A NCAC 02H.1005 (3) apply. tinder this
paragraph, "Low, Densiiy" projects (l.e., projects for which structural stomBwater
controls are not required) are defined as developments having a built upon area of
30 percent or less. Low Density projects must also feature stormwaber runoff
transported primarily by vegetated conveyances, a stormwater conveyance system
which doers not include a discrete stormwater collection system, and a 30 foot wide
vegetative buffer adjacent to surface waters. "High Density" prza is (I.e., pro"
for which moral stormwater controls are required) are projects involving more
than 30 percent built -upon area. High dmnsity projects require stormwater control
systems which must be wet detention ponds, infiltration systems or "alternative
stormwater management systems," and which must be designed to control runoff
fi o n all surfaces generated by one inch of rainfall.
Historically, development projects at the Wilmington international Airport have
been permitted under the "Law Derma" option, due to the overall built -upon
surface area on airport property, wMhich is well under 30 percent. In May of 2001,
the iocai office of NCDENR advised the airport in writing that "additional built -upon
area at the Airport cannot be permitted under the Low Denft option until a
Master Drainage Plan is submitted to and perms by this office." The regulatory
basis for stormwvater master plan permits is found at 15A NCAC 02H.1003 (h)(3).
Officials from the Wilmington office of NCDENR have provided verbal guidance
regarding NCDENR pollol and practice relative bo master plan permits. The
following discussion paraphrmw that guidance. A facility may receive a master
plan permit under either high density or low density provisions. Facilities with ar,
PaW13

V VMington International AiTort (ILM)
Storm -water
overall built -upon area density in excess of the high density threshold would be
required th .hold a high density master plan wit: These facilrities would be
required to implement high density BMP controls for all development projects
involving an increase in butt -upon area. Facilities with an overall built -upon area
density below the high density threshold would be allowed to hold a low density
master plan permit, even if certain areas within the facility site are characterized as
pockets of high density development. Facilities with a low density master plan
penrlt would be allowed to construct development projects which are consistent
with low density criteria without implementing high dimity BMP controls. For
development projects characterized as pockets of high density development at
facilities with a low density master plan, NCDENR would require implementation of
high density BMP controis.
NCDENR officials advise that three cr1teeria are evaluated in making a determination
as W whether a development mr4ect psi 11 be charactetized as a pocket of high
density development The criteria for high density pockets are as fblbws:
1. Built -upon surfaces in high density pockets are clustered
(concentrated) together geographically within the fbaft site.
2. Nigh density podeft are drained by stormwater collection systems.
3. Built -upon surfaces in high density pockets do not drain by shy ftw
across vegetated surfaces.
This Stormwater Master Plan is based on overall low density with anticipated
pockets of high density development
The existing runway and taxiway complex on the airfield are considered to be
consistent with low density criteria because the built -upon surfaces are distributed
through the site and the built upon. surfaces gain by sheet flown over large grass
areas. The runway and taxiway c complex is served by a stormwater collection
system which prelates the Storrnwater Rules and which collects the runoff:

Wilmington International Ahport (ILM)
Sto� 'r-aste-, Plal!
downstream of the sheet flow areas.
. Kew- tia��� County Storm Water +i_nagement Ordl-Aanae
New Hanover County adopted a Storm Water Management Ordinance on
September 5, 2000. A copy of the ordinance is included as Appendix B. The
ordinance requires peak flow attenuation for new development in the County such
that peak flow rates for post -development conditions do not exceed peak stow rates
for pre -development conditions for 2-year, 101ear and 25-year sbxrn events.. For
redevelopment activities, the ordinance requires peak flow attenuation for a 10-
year event The design of extended dry detention basins on the airport must
satisfy these requirements.
VM Wildiife Hazard C udderattilons
Wildlife activity on and in the vidnIty of airports resents a serious hazard to
aviation safety. On May 1, 1997, the Federal Aviation Administration (FAA) issued
Advisory Circular No. 150/52a0-33, "Hazardous VViiidiife Attractants On Or Near
Airports," (the `Widlife AC"). A draft revision of this document was issued by FAA
on January 30, 2004. The revised AC, designated as No. 150/5200-33A, was
issued on July 27, 2004. A copy of the current AC is included In Appendix C.
The Wildlife AC was developed by FAA from a nation-wide perspective. During
development of the scope of work for the Stormwater Faster Plan project;, the
wildlife hazard issue relative to stormwater BMP design was recognized as a key
Issue in development of the Plan. It was considered prudent to review wildlife
concerns from a iocai, site specific perspective as well as in the nation-wide context
of the Wildlife AC. The united States Department of Agriculture, wildlife Services,
has provided this local perspective, based on site visits to the airport and
discussions with Talbert & Bright and airport staff. A letter report summarizing the
findings and recommendations of Wildlife Services Is indudled In Appendix D.
Page-15

Wilmington International Airport (ILM)
q. T i
The Wildlife Service report states that the guidance of. the W!#dW- AC is applicable
to the Willmington International Airport. The report strongly advocates avoidance
of wet detention basins and recommends the use of extended dry detention basins
for stormwater management. The report provides further recommendations
relative to the design details for extended dry debention basin and grassed Swale m
BMP's on the airport.
The Wildlife AC provides guidance on the design of stormwater detention basins on
airports. Specifically, the AC stipulates the use of steep -sided, narrow, linearly
shaped (dry) detention basins with a maximum detention time of 48 hours fbr the
design storm.
Most large development projects in coastal Southeastern North Carolina utiCiZe wet
detention basins as the primary stormwater BMP. Use of wet basins for the
Wlmingtan International Airport was achy studied during plan preparation,
however due to the wildlife hazard issue, it has been determined that stormwater
management at the Wilmington International .Airport should be accomplished
primarily with a combination of extended dry detention banns and grassed swales
needed to meet the required 85% pollutant removal efficiency stipulates! under
North Carolina stoimwater rules. NCQENR has assigned a removal efcleney of
50% to the eWonded dry detention BMP and 35% to the grassed swale BMP. The
extended dry detention basins will also serve tD meet the peak discharge
attenuation requirements of the New Hanover County Storm Water Management
Ordinance.
Wet detention. ; basins, extended detention wetlands, pocket wetlands, bkwet mftn
areas, infiltration devices, and other BMPs which involve a permanent pool of open
water., water quality draw -awn times exceeding 48 hours, and/or artiftia# wetland
Page-lf

Wilmington Internationad Airport (ILM)
-SfCrr.-w L':-r 11.aszep Plail
type conditions will be excluded from consideration at the Wilmington International
Airport These BMPs are generally aqxcted to create conditions #tat attract Wid!;fe
species which are hazardous to .avlation. In accordance with the Wildlife AC,
creation of these potential attractants of hazardous wildlife- roust be avoided.
37G P+opomW BMP Dc*N+gjv CAteria
Design criteria specific to the Wilmington International Airport have been
developed for extended dry detention basins and grass swales. The a terla are
Based on the requirements set forth in the North Carolina Storrnwater Rules,
guidance in the NCDENR Stormwater BMP Manual (see Append"o( E), the
requirements of the New Hanover County Storm Water Management Ordinance
and the requirements of FAA AC 150/5200-33A, "Hazardous Wildlife Attractions on
or Near Airports". The following is a list of aitexla developed using the prey,
mentioned documents:
amended Dry Basins
1. The basin si-ould be p-Mcled, narrow, and iinearly-shaped.
2. Capture the runoff from a 1" rainfall and release over a period of 48 hours.
3. Provide a minimum flow leng"-basin width ratio of 3:1
4. Provide side slopes in the range of 3:1 to 4:1 {horizontal: vertical).
S. ]install outlet orifrce in an dosed structure with a sump. Provide a trash
rack on the inlet to the structure. Do not provide an open permanent pool.
6. Provide a rip -rap or concrete lined low -flow channel from inlet to outlet with
a minimum depth of one (1) foot.
7. Slope basin bottom at a 2% preferred and 1% minimum grade toward low
flow channel.
8. Provide heavy equipment access for clan -out and maintenance.
9. Provide excess storage in the tower levels of the basin amounting to 20% of
the 1" rainfall event runoff volume.
10. Provide for peak flow attenuation above the 1" storm storage, in
accordance with the New Hanover County Storm Water Management
Page-17

Wilmington International Airport (ILM)
Stormwarer blaster Plan
Ordinance.
11. Provide for seeding the basin bottom side slopes and berms with common
Bermuda grass or odw appropriate mix. Seed mixture shall not contain any
form of millet, rye grass or other large seed producing grasses.
12. Stabilize the basin within 14 days of construction completion.
13. To the extent possible, position the bottom of the basin above the seasonal
high water table.
14. Provide for safe conveyance of a 100-year storm event.
1. Swales will typically be located upstream of extended dry detention basins.
2. Provide a 0.2% minimum to 4.0% maximum longitudinal slope.
3. Provide side shapes no steeper than 3:1 (horizontal: vertical) with 5:1
preferred. The swale moss section should be triangular or parabolic.
4. Swale bottom should be located above the seasonal high water table.
5. 9wales should be designed for ready mowing with standard mowing
equipment.
6. Flow Veloft should be limited to 2 fleet per second for the 2-year design
flow and a non -erosive velocity for the 10jear design ftm.
7. An attempt shall be made to provide 100 linear feet of swat per acre of
drainage area. No less than 50 linear feet of Swale per acre shall be
prov'ded.
8. Provide for seeding the swale with common Bermuda grass or otter
appropriate mix. Seed In'ixture shall not contain any form of miile% rye
grass or other large seed producing grimes.
9. Stabilize the swale within 14 days of construction completion.
X, Proposed Of sn^water Management Concept
This plan presents two solutions to stormwater management for the west side of
the Wilmington international Airport. These two solutions include a centralized
Page-18

Wilmington Internatiomd Airport (ILM)
'st ,�Yr 1. V a er 11aster Mara
stormwater management concept and a distributed stormwater management
concept. Both concepts will require won of new stormwater conveyance
pipelines to serve the west side of the airport properly. Discussion of each concept
is included in the following sections.
The extended dry detention basin and stormwater conveyance pipeline designs
included and depicted in this Flan have been developed to the conceptual design
level only. Final design, supported by topographic survey, wetlands delineation
and subsurface exploration efforts, must be undertaken for all faoIities prior to
The extended dry detention basin designs have been developed with an assumed
development density of 65% butt -upon area for extended dry detention basin No.
1 and for the distributed concept example basin. An assumed density of 60% was
used in the design of extended dry detention basin No. 2.
Centralized Stormwater Management Concept
The Centralized Stormwater Management Cow involves _stormwater conveyance
to centralized stormwater detention facilities for treatment and control of peak
flaws. This concept is depicted on Rgure/Plan Street PR1.1. In the centralized
concept, two large extended dry detention basins would be constructed to serve
the future built -upon areas on the west side of the airport.
Extended dry detention basin No. 1 would be located south of Airport Boulevard
and is sized to capture and treat runoff from approximately 328 acres. The area
draining to this basin includes the airport business park
deveiopmentjredevelopment, the aldine terminal facility expansion and the GA
apron expansion/redevelopment area. Conveyance of stormwater from the
individual project sites will be through a new, stormwatw conveyance .system,
Included as part of this master plan. Stormwater will discharge from basin No. 1
through four outlet control structures located at existing airport outfali points.
page-19

Wilmington International Airport (IL )
Outfall structures are sized to limit flow lift downstream channels to
predevOe opment peaks to minimize any erg or ration of the eking
channels. Three of the outfaii points flow through open channels to Smith Creek.
The other outfall paint will be through an existing culvert under 23d Street.
Fdended dry detention basin No. 2 would be looted west of Runway 17 35, with a
portion of the Eras',n located between the Runway and Taxiway W and the second
portion of the basin located north of Taxiway W. These two basin areas w411 be
interconnected with a 60' pipe. Extended dry detention basin No. 2 is sized to
capture and treat runoff from approximately 164 acres and will be used to provide
brabinent for stormwater runoff from the General Aviation facilities expansion area
and other aviation related or commercial development along Trask Drive, north of
the existing General Aviation area. Stormwater Ml discharge 1 No. 2
through three outlet control structures connected to existing stormwater pipelines.
Concrete or rip -rap low flaw channels will be constructed in the bottom of both
basin No. i and No. 2 to help maintain a dry basin bottom as mquired by the
Wildlife AC and to facilitate maintenance. Bath extended dry detention basins are
designed to treat the runoff from a r rainfall event:, along with attenuating the
peak flow leaving the airport property for 2-year, 10-year and 25-rear storm
events. The basins will also be able to safely convey a 100-year storm event.
Computations are included in the technical appendix.
Distributed Stormwater Management Conaerxt
The distributed Stonnwater Management Concept is based on the idea that
stormwater is detained and treated locally at each project site and then conveyed
off airport property. This concept is depicted on Figure/Man Sheet PR1.2. The
distributed concept will be used only fior the approximately 328 acres of land which
drain to extended dry detention basin: No. i in the centralized concept. Anticipated
development in this area includes airport business park development, airline
terminal facility expansion and general aviation facility expansion. The 164 acres
Page-20

Wilmington International Airport (ILM)
Stormwater 3 as:er P Lip:
of land discussed in the centralized stormwaber management concept that drains to
extended dry detention basin No. 2 will also drain to this basin in t4e distributed
One example extended dry detention basin design has been completed for the
distributed concept. The example basin would serve the general aviation, long
term parking and rental car parking expansion projects. Computations are included
in the technical appendix. Individual extended dry detention basins have been
sized approximately for each development area, using a ratio of basin area to
tributary area developed from the example basin design. An outlet control
strucdbure will be constructed in each basin to control flow Into the sWn water
conveyance system included as part of this master plan. The untended dry
detention basins sized for the master plan are based on the Idea that each
development area will have one basin. The actual number, location and size of the
distributed basins will depend on the nature and scope of individual airport and
tenant projects as they arise.
Concrete or rip -rap lined low flow dwinnels, will be constructed in the bottom of all
basins to help maintain a dry basin bottom as required by the Wildlife AC and to
facilitate maintenance. AN dry detention basins will be designed to treat the rurx ff
from a 1" rainfall event:, along with attenuation of the peak flow leaving the airport
property for the 2-ywr, to -year and 25-year storm events. 7he basins will also be
able to safely convey the 100 year storm event.
StDmrwater Conveyance Plpelines
Both the centralized concept and the distributed caret will require constructim
of stormwater conveyance pipelines to collect and convey runoff from the 328 acre
development area tributary to extended dry detention basin No. 1. The
conveyance system consists of three pipelines !A, B and Q located within the
Business Park Development area. Conveyance system A will be used to carry
runoF from the G+, terrininal expanfor, area, aldine terminal expansion, area and
Page-21

Wilmington International Airport (ILM)
the portion of the Business Park Development area north of Hewlett Drive and east
of Gardner Drive. Conveyance system B will be used to carry runoff from the
Business bark Development area north of Airport Boulevard, east of Gardner Drive
and south of Hewieft Drive. Conveyance system C will be used to carry runoff from
the Business Park Development area north of Airport Boulevard, west of Gardner
Drive and extending north to gain the existing forested depression to be used as a
deten! basin located adjacent to Blue Clay Road.
The size of the conveyance system pipelines varies based on the management
concept. For both cam, the Conveyance system is smed to convey 25 year
storm flows with minimal surcharge (hydraulic grade lure no more than 2 feet
above the pipe crown). For the centralized concept;, the pipelines vwll be larger
than for the distributed concept since they will be required to convey runoff directly
from the development area without any peak flow attenuation. The pipelines well
outlet into extended dry detention basin No. 1 which will treat and attenuate the
flown prior to leaving the Airport.
For the distributed concept, the pipelines vWl be .smaller than fir the centralized
concept since they will convey the attenuated sto.mwater flows from the
distributed -basins. The pipelines will outlet into a distribution system that WIN
distribute the runoff to existing Airport outfall pipes and channels.
Cost 90nions for Stormwater Management Conte
Cost opinions; have been developed for the stormwater management concepts
developed for the west side of the Airport. These cast opinions are intended solely
as budgetary planning tools. More detailed cost opinions should be developed for
individual system components during the project design development process to
verify budgetary considerations.
The total cost opinion for the centralized cone, in 2004 dollars, is $9.7 Million.
The total cost opinion %r the distributed concept, in 2004 dollars, is $10.7 Million.

Wilmington International Airport (ILM)
Storrnwater �eiuster Plan
Cast opinion worlds are presented in Appendix"-".
Construction of infrastructure Improvements for both stormmanagement
concepts can be phased to spread Implementation costs over a period of Urne as
development progresses. The distributed concept can be more readily phased than
the centralized concept A phasing plan (plan suet rPHU) has been prepared for
the distributed concept The plan presents four phases of construction. Costs for
each phase have been divided between Airport costs and tenant costs. phase one
would include expansion of the existing airline terminal parldng lot and expansion
of the existing general aviation area. The work would include construe of an
extended dry detention basin for each development area which would initially
outlet into the existing drainage conveyance system (and ultimately into the new
conveyance system). The cost of the basins would be an Airport cast Prase one
would also include development of two business park sides directly south of Airport
Boulevard which would also require extended dry detention basins for each
development area. Construction of these stormwater basins world be a tenant
cosL The distributed concept phasing there progresses to the north in three
additional Increments.
XT. metho&lnagy
The SCS unit hydrograph method has been used for project hydrology,
implemented using PondPack software from Haestad Methods, Inc. CN and time of
c oncenhation data were developed using SCS TR 55 methods. The hydrologic son
groups firer the various soil units on the airport were taken from the Appendix A
listing of TR 55. The SCS soil map for New Hanover County was used to Identify
r
soil units. For soiis with multiple hydrologic soil groups, the lowest (most well
drained) group was used. Jhe SCS type M 24- our rainfall distribution was used.
Rainfall depths were taken from the New Hanover County Storm Water Design
Manual. FHWA pipe curt hydraulic: data and standard weir and orifice hydraulic
methods were employed. Pipeline hydraulic grade lines were computed using
Page-23

Wilmington International Airport (ILM)
e
i
StorinCad software, also from Haestad Methods, Inc.
For extended dry detention basin design, the runoff volume for the one inch rainfall
event was estimated using the Schueler equation;
Rv=.009(I)+.05
The required 20% sediment storage was computed based on this volume, and was
assumed to occupy the lowest level of the basin on either side of the low flow
channel. For the PondPack model, this volume was subtracted from the stage -
storage curve. The SCS method yields very low runoff volumes for a 'nch 24-
hour rainfall, due to the standard initial abstaction. Therefore, a higher 24-hour
rainfall was input into the PondPack model such that the model would generate a
runoff hydrograph with a volume equal to that predicted by the Schueler equation.
This hydrograph was then routed throto the basin In order to size the dewatering
device to drain the runoff from the equivalent 1'® design storm In approadmately 48-
hours (this detention time is dent with the minimum required to meet
NCDENR ulteria and the maximum consistent with the Wiild1fe AQ. The drain time
was taken as the cltferenc:e in time from the start of outflow W the end of outflow
in the basin routing outflow hydrograph. Reservoir routings were completed fbr 2-
year, 10-year, 25-year and 100-year ralnfall everts as well, in order to size the
peak attenuation storage and outlet structures, confirm pre- versus post -
development peak discharge control, and confirm the safe passage of a 100-year
event.
Xg. Lmpiememlation of StmmwaW Coobvils
Stormwater controls will be implemented on an Incremental basis as high density
development involhAng a net increase in bullt upon area occurs. It is not the invent
of the Airport Authority to Implement BMP's W serve areas that are already
developed as of the date of this Plan, nor for redevelopment of such areas (to the
Page-24

Wilmington International AiTort (ILM)
�
�f torr2'ti''!er Visas!erP:.28t
extent that such redevelopment does not result in a net increase in impervious
surfacing).
XECE. Alternadve Sokdkm and Plan Modification
This Plan has been developed based on analysis, study and consultation with
airport staff. It presents workable solutions to the long term storm water
management needs of the airport The plan is conceptual in nature.
Implementation of the Plan will depend in large part on the exact nature,
magnitude and sequence of development projects which move forward, and on
funding resouroes which becorne available for construction of sh mwater
improvenxn ts. Nothlr,1 'In tali plan is intended to limit or restrict the airport or its
current or pect�je tenants mth rmp-,ct to pursuing alternate or modified
stormwater management solutions in various locations.
Page-25

IN
Hydrologic Soil
Symbol Name Group
Be
Ba meade
A
Bp
Borrow Pit
--
JO
Johnston
D
Le
Leon
LS
Lynchbura
C
No
Norfolk
B/D*
On
Onslow
B/D*
Pn
Pan o
D*
Ra
Rains
B/D*
Se
Seagate
D*
St
Stallincis
C
Wr I
IM ' htsboro I
C
*- First soli group denotes drained condition
while the second denotes undrained condition.
Sources:
New Hanover County Sail Map
Exhibit A, SCS TR55, 2nd Ed., 6/86

11
0
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u
V) O
U o w
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s' O N
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•oea 'ATMM - na 1GW1 aoz 'ec My 'awaaYo•M-6we�ot�lsp,wJ,1,L—a �oY1wM\�a6w, \ a7n^v\�a.

®
Stream Identifier
®
Wetland Identifier
b
Wetland Flag
*
Field Data Station
—� Ditch
Culvert
Intermittent Stream (R4)
Ephemeral Stream (R6)
Stormwater Ponds
Wetlands
R' Palustrine Open Water (POW)
E— Relatively Permanent Water
1. Waters of the U.S. within the project study limits have been located
using submeter, Sluetooth GPS antennas by Timmons Group.
2. The eastern half of this site was delineated by Timmons Group as an
addendum to the wetland area previously delineated by WithersRavenel
and approved by the U.S. Army Corpo of Enginocr on 12212010
(SAW-2010-01904).
3. Waters of the U.S. delineated by S. Thebert and S. Law on 09/182019
and 10/D4/2019.
4. Waters of the U.S. have not been confirmed by the U.S. Army Corps of
Engineers until stamped.
5. Project limits are approodmale.
6. Topography based on USGS MAR.
7. Cowardin Stream Classifications are based solely on field
observations. No formal Stream assessment methodology was
completed to determine these Cowardin Classifications.
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JOB NUMBER
37630.054
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1 OF 1
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