SW7020908_HISTORICAL FILE_20021015

STORMWATER. DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW Z�9 %&
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
HISTORICAL FILE
DOC DATEti)GDI�
YYYYMMDD

r
October 14, 2002
Mr. Bill Moore
NCDENR — Division of Water Quality
943 Washington Square Mall
Washington, NC 27889
RECEIVED
OCT 15 2002
DWQ-WARO
RE: Dare County Regional Airport
Overlay Parallel and Stub Taxiways, 'taxiway "D" and Apron Expansion
TBI No. 2301-0101
Dear Mr. Moore:
I appreciate you taking the time to visit the Dare County Regional Airport on Wednesday
morning, October 10, 2002 to discuss the stormwater permit issues for the referenced project. As
we discussed the airport has historically been permitted as a low density area as noted in our
original application dated August 2002. You expressed some concern as to whether or not the
low density option should be available to the airport due to a "high density pockets" located
within the airport property. You mentioned that in the past you have permitted projects with a
"hybrid permit" which allows the property to remain a low density area, and would permit this
project in a similar fashion.
As discussed, stormwater runoff from the proposed apron will be treated using an infiltration
basin with a wide bottom and flat side slopes. The original swale designed for the project was
more than adequate for capturing the first 1.5" of runoff from the apron, however the swale side
slopes were steep and would be difficult to maintain. A new basin configuration has been
developed to allow for maximum 5:1 side slopes and a wide bottom to increase the surface area
for infiltration. The top of the storage volume will be at elevation 8.0 and the bottom will be at
elevation 6.0. 'file elevation of 8.0 was set using the elevation of the concrete apron around the
existing drop inlet that will be used for runoff in excess of the Swale volume. Overflow from the
basin storage volume will spill into the vegetated area surrounding the basin and drain into the
existing drop inlet. The required storage volume for the infiltration basin is 14,370 cubic feet
and the proposed swale will provide a volume of 14,375 cubic feet with a basin bottom area of
6,500 square feet.
Based on historical data taken from soils reports performed at different times of the year, and
from the soils report performed with this project the seasonal high water table is approximately
4.5 to 5 feet below ground. The existing ground elevation at the location of the infiltration basin
is 9.5, giving a water table elevation of 4.5 to 5.0 above mean sea level. This will provide a
separation of 12" to 24" between the bottom of the basin and the water table. You mentioned
during the site visit that you would like to have at least 12" separation. The bottom elevation of
I NGINL:F;RING & PLANNING CONSUIYANTS
W11'11'.TA1.BF 1'ANDBRK) FITCONA
4810 SHELLEY DRIVE WILMINGTON. NC 28405 910.7635350 FAX [phone]
WILMINGTON. NOM-11 CAkOLINA • CIIARLO TF.. NOU11 CAROLINA • RICHMOND, VIRGINIA

the proposed basin is constrained by the invert elevation of the outlet pipe from the new apron
being at elevation 6.0. To maximize the distance from the water table and bottom of swale, a
localized area at elevation 6.0 was provided for the outfall pipe from the apron, and the
remainder of the swale bottom was set to 6.5. Infiltration rates were not available in the soils
report for this area, therefore a rate of 7 inches per hour was assumed. This will provide a
drawdown time of 3.7 hours. if we used the minimum allowable hydraulic conductivity of 0.52
inches per hour (as noted in checklist item h) for calculation purposes, the drawdown time is 50
hours, still much less than the required five days. We feel very certain that the infiltration rate of
the soils present is much better than 0.52 inches per hour and should not have any trouble with
infiltration based on this constraint. This proposed infiltration basin will meet the requirements
for this "high density pocket", however we would still like the airport to be classified as a low
density area since the total impervious area is less than 25% of the total area.
Attached to this letter is the infiltration Basin Supplement. The Operation and Maintenance
Agreement signed by the Airport Manager is being sent to you directly from 'rim Gaylord. As
we discussed the Operation and Maintenance Agreement applies to maintaining the basin while
in service and does not prohibit future expansion over the existing basin. We understand this
agreement does not prevent the Airport from demonstrating compliance or eligibility for the low
density option of any future project at the Dare County Regional Airport. I have also include a
sketch showing the proposed basin (I1"x17") and two sets of revised plans (24"06") as per
your request.
Again I would like to thank you for your time regarding this project. As I mentioned the airport
is ready to begin construction so please let us know what additional information if any is
required to expedite the approval process. If you have any questions please do not hesitate to
cal1.
Yours truly,
John M. Massey, P. E.
C: Mr. Tim Gaylord

Permit No.
(to be provided by DWQ)
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
INFILTRATION BASIN SUPPLEMENT
This form may be photocopied for use as an original
DWQ Stormwater Management Plan Review:
A complete stormwater management plan submittal includes a stormwater management permit application, an
infiltration basin supplement for each system, design calculations, soils report and plans and specifications
showing all stormwater conveyances and system details.
I. PROJECT INFORMATION
Project Name: &(LS C.oJn3T� IZECo'o, ^t, ANa-foi t - APea,-) CCpa..�S�.�•.1
Contact Person: J o u -1 IA a SS EJ Phone Number: ('?I D ) -7
This worksheet applies to: Basin No. in Drainage Area
(as identified on plans) (from Form SWU-101)
11. DESIGN INFORMATION - Attach supporting calculations/documentation. The soils report must be
based upon an actual field investigation and soil borings. County soil maps are not an acceptable source
of soils information. All elevations shall be in feet mean sea level (fmsl).
Soils Report Summary
Soil Type
Infiltration Rate
SHWT Elevation
Basin Design Parameters
Design Storm
Design Volume
Drawdown Time
Basin Dimensions
Basin Size
Basin Volume Provided
Basin Elevations
Bottom Elevation
Storage Elevation
Top Elevation
Form SWU-103 Rev 3.99
5A,St> C50 11411(.t054:
' inlhr r cf/hr/sf (circle appropriate units)
"1 QGQ JoL ;
i , 5" To $, O fmsl (Seasonal High Water Table elevation) xz') �l`'H,gis�eSF
x I'-1 !?70GK
1. S inch (1.5 inch event for SA waters, 1 inch event for others)
j 3? o c.f.
3,1 4ayZ— 4-bag,s
3 4> ft. X 570 ft. = w, �oD ,sq. ft. (bottom dimensions)
S c.f. -L Ar 545.0
7,5, 12,19 G F A,'r E L.6 J A-n o .0 �. Q
(0.0 fmsl
6,0 fmsl
5.0 fmsl
Page I of 3

III. 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, February 1999) and Administrative Code
Section: 15 A NCAC 2H .1008.
Initial in the space provided to indicate that 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. Attach justification if a requirement has not been met.
a3
Applicants Initials or +^ ° �'�
a. System is located 50 feet from class SA waters and- 30 feet from other surface waters.
b. System is located at least 100 feet from water supply wells.
c. Bottom of system is at least 2 feet above the seasonal high water table. (I • e`� 2 ' o s °'
d. Bottom of the system is 3 feet above any bedrock or impervious soil horizon.
e. System is not sited on or in fill material or DWQ approval has been obtained.
� A £ System is located in a recorded drainage easement for the purposes of operation and,
maintenance and has recorded access easements to the nearest public right-of-way. r
g. Drainage area for the device is less than 5 acres.
h. Soils have a minimum hydraulic conductivity of 0.52 inches per hour and soils report is
attached.
i. System captures and infiltrates the runoff from the first 1.0 inch of rainfall (1.5 inch event for
areas draining to SA waters ). Design volume and infiltration calculations attached.
j. System is sized to take into account the runoff at the ultimate built -out potential from all
surfaces draining to the system, including any off -site drainage. Calculations attached.
k. All side slopes stabilized with vegetated cover are no steeper than 3:1 (H:V).
�J-�aE .,pcbJ
1. A pretreatment device such as catch basi grease trap, filter strip, grassed swale or
sediment trap is provided.
m. Bottom of the device is covered with a layer of clean sand to an average depth of 4 inches or
dense vegetative cover is provided. C 3 tom, s s
5 +-t n. Vegetated filter is provided for overflow and detail is shown on plans (Required minimum
length is 50 feet for SA waters, 30 feet for other waters).
I� A o. Flow distribution mechanism within the basin is provided.
p. A benchmark is provided to determine the sediment'accumulation in the pretreatment device.
q. Runoff in excess of the design volume bypasses off-line systems (bypass detail provided).
r. System is designed to draw down the design storage volume to the proposed bottom
elevation under seasonal high water conditions within five days. A soils report and all
pertinent draw -down calculations are attached.
s. Plans ensure that the installed system will meet design specifications (constructed or
restored) upon initial operation once the project is complete and the entire drainage area is
stabilized.
Form SWU-l03 Rev 3.99 Page 2 of 3

IV. IlVFILTRATION. BASIN OPERATION AND MAINTENANCE AGREEMENT
1. . After every runoff producing rainfall event and at least monthly inspect the inf ltration system for erosion,
trash accumulation, vegetative cover, and general condition.
2. Repair eroded areas immediately, re -seed as necessary to maintain adequate vegetative cover, mow
vegetated cover to maintain a maximum height of six inches, and remove trash as needed.
3. After every runoff producing rainfall event and at least monthly inspect the bypass, inflow and overflow
structures for blockage and deterioration. Remove any blockage and repair the structure to approved design
specifications.
4. Remove accumulated sediment from the pretreatment system and infiltration basin annually or when depth
in the pretreatment unit is reduced to 75% of the original design depth. The system shall be restored to the
original design depth without over -excavating. Over -excavating may cause the required water table
separation to be reduced and may compromise the ability of the system to perform as designed. Removed
sediment shall be disposed of in an appropriate manner and shall not be handled in a manner that will
adversely impact water quality (i.e. stockpiling near a stormwater treatment device or stream, etc.).
A benchmark shall be established in the pretreatment unit. The benchmark will document the original
design depth so that accurate sediment accumulation readings can be taken. The measuring device used to
determine the depth at the benchmark shall be such that it will give an accurate depth reading and not
readily penetrate into accumulated sediments.
When the design depth reads tO - ; - feet in the pretreatment unit, the sediment shall be
removed from both the pretreatment unit and the infiltration basin. 6 0 Ite.,t ,sr r. w ,, Ava L*
A-r +7otle dV TL.tcT t S F,"v) .J trr+ 6Ct)&-4r&,3't"). aIL '..(A" to/*P)
5. If the Division determines that the system is failing, the system will immediately be repaired to original
design specifications_ If the system cannot be repaired to perform its design function, other stormwater
control devices as allowed by NCAC 2H .1000 must be designed, approved and constructed.
I acknowledge and agree by my signature below that I am responsible for the performance of the five
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to any
changes to the system or responsible party.
Print Name and Title:_ William T. Gaylord, Airport Director,-,
Address: P 0 429, Manteo, NC 27954
252-473-2600
Date: October :14, 2002
Note: The legally responsible party should not be a homeowners association unless more than 50% of the lots have been sold and a
resident of the subdivision has been named the president.
I, Crystal Sidwell a Notary Public for the State of North Carolina County of
Dare do hereby certify that William T . Gaylord personally appeared before me this____
day of October 14_ 2002 and acknowledge the due execution of the forgoing infiltration basin maintenance requirements.
%JIM814r(,Ag1�
Witness � d qg� seal;
• -C - ' SEA1fJ ? �p'tARY My commission expires May 16 2007
pV 6 L'1G C.
9
Form 1d3 • •Re%iPage 3 of 3
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1. UNDERGROUND UTILITIES INCLUDING WATER UNE9, ELECTRIC SERVICE AND TELEPHONE SERVICE a.x.e Aus�Aa�
ARE LOCATED WITHIN THE CONSTRUCTION AREA_ APPROXIMATE LOCATIONS OF UTILITIES ARE
SHOWN ON SHEET 22. THE CONTRACTOR IS RESPONSIBLE FOR LOCATING ALL UTILITIES PRIOR TO "_t Hu
BEGINNING CONSTRUCTION. ANY DAMAGE TO UNDERGROUND UTILITIES DUE TO CONSTRUCTION 2�m-[nm
ACTIVITIES SHALL BE REPAIRED IMMEDIATELY. COST OF REPAIRS ARE TO BE BORNE BY THE 30 15 0 30 60 90
CONTRACTOR,
2. SEE SHEET 25 FOR TYPICAL PAVEMENT SECTIONS AND DETAILS, 2 3
3. SEE SHEET 26 FOR PROPOSED STORM DRAIN PROFILE AND DROP INLET DETAILS, SCALE IN FEET
4, SEE SHEETS 25 AND 28 FOR LIGHTING, WINDCONE AND ELECTRICAL PLAN AND DETAILS. 1.- 30