20041743 Ver 2_More Info Received_20080520

ILY? THE LPA GROUP of North Carolina, p.a.
Transportation Consultants
5000 FALLS OF NEUSE ROAD ¦ SUITE 304 ¦ RALEIGH, NORTH CAROLINA 27609 ¦ 919-954-1244 ¦ FAX [phone]
May 19, 2008
Ms. Annette Lucas
NCDENR, Division of Water Quality
DWQ 401 Permitting Unit
2321 Crabtree Blvd., Suite 250
Raleigh, North Carolina 27604
Re: Martin County Airport
Taxilane Development
Dear Annette:
D?f -I193 ?z
Enclosed please find two copies of the plans, calculations, BMP Checklist, and soils
report for the above referenced project for your review and approval. Also enclosed is a
signed and notarized copy of the of the Operation and Maintenance agreement for the
wet detention pond.
The enclosed plans correspond to the first phase of development in the taxilane area.
The initial project consists of the construction of three taxilanes to be used for access to
a t-hangar building as well as future corporate hangars. This initial phase also includes
the construction of a wet detention pond that has been designed for the full buildout of
this area.
The plans for this project have been packaged together with a separate parallel taxiway
project that is to be bid at the same time. Due to the amount of excess information,
have only enclosed the plan sheets that are relevant to the taxilane development and
the pond. If you think you need additional sheets, let me know and I'll get them to you
as soon as possible. The required check, in the amount of $570.00, was submitted in
December.
If you have any questions or need additional information, please do not hesitate to call.
Sincerely,
THE LPA GROUP of North Carolina, p.a.
aso L. Elliott, EI
Aviation Design
Enclosures
Member of THE LPA GROUP INCORPORATED
rzn
MAY ? 2.008

ATLANTA ¦ BALTIMORE ¦ BATON ROUGE ¦ CHARLOTTE ¦ COLUMBIA ¦ GREENSBORO ¦ IRVINE ¦ JACKSONVILLE ¦ KENNESAW ¦ KNOXVILLE ¦ LITTLE ROCK
McLEAN ¦ MOBILE ¦ NASHVILLE ¦ OCEAN SPRINGS ¦ ORLANDO ¦ RALEIGH ¦ SARASOTA ¦ TALLAHASSEE ¦ TAMPA ¦ WEST PALM BEACH
Permit Number:
(to be provided by DWQ)
Drainage Area Number:
Wet Detention Basin Operation and Maintenance Agreement
I will keep a maintenance record on this BMP. This maintenance record will be kept in a
log in a known set location. Any deficient BMP elements noted in the inspection will be
corrected, repaired or replaced immediately. These deficiencies can affect the integrity
of structures, safety of the public, and the removal efficiency of the BMP.
The wet detention basin system is defined as the wet detention basin,
pretreatment including forebays and the vegetated filter if one is provided.
This system (check one):
? does ® does not incorporate a vegetated filter at the outlet.
This system (check one):
? does ® does not incorporate pretreatment other than a forebay.
Important maintenance procedures:
- Immediately after the wet detention basin is established, the plants on the
vegetated shelf and perimeter of the basin should be watered twice weekly if
needed, until the plants become established (commonly six weeks).
- No portion of the wet detention pond should be fertilized after the first initial
fertilization that is required to establish the plants on the vegetated shelf.
- Stable groundcover should be maintained in the drainage area to reduce the
sediment load to the wet detention basin.
- If the basin must be drained for an emergency or to perform maintenance, the
flushing of sediment through the emergency drain should be minimized to the
maximum extent practical.
- Once a year, a dam safety expert should inspect the embankment.
After the wet detention pond is established, it should be inspected once a month and
within 24 hours after every storm event greater than 1.0 inches (or 1.5 inches if in a
Coastal County). Records of operation and maintenance should be kept in a known set
location and must be available upon request.
Inspection activities shall be performed as follows. Any problems that are found shall
be repaired immediately.
BMP element: Potential problem: How I will remediate the problem:
The entire BMP Trash/debris is resent. Remove the trash/ debris.
The perimeter of the wet Areas of bare soil and/or Regrade the soil if necessary to
detention basin erosive gullies have formed. remove the gully, and then plant a
ground cover and water until it is
established. Provide lime and a
one-time fertilizer application.
Vegetation is too short or too Maintain vegetation at a height of
long. approximately six inches.
Form SW401-Wet Detention Basin O&M-Rev.3 Page 1 of 4
Permit Number:
(to be provided by DWQ)
Drainage Area Number:
BMP element: Potential problem: How I will remediate the problem:
The inlet device: pipe or The pipe is clogged. Unclog the pipe. Dispose of the
swale sediment off-site.
The pipe is cracked or Replace the pipe.
otherwise damaged.
Erosion is occurring in the Regrade the swale if necessary to
swale. smooth it over and provide erosion
control devices such as reinforced
turf matting or riprap to avoid
future problems with erosion.
The forebay Sediment has accumulated to Search for the source of the
a depth greater than the sediment and remedy the problem if
original design depth for possible. Remove the sediment and
sediment storage. dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Erosion has occurred. Provide additional erosion
protection such as reinforced turf
matting or riprap if needed to
prevent future erosion problems.
Weeds are present. Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the plants rather than spraying.
The vegetated shelf Best professional practices Prune according to best professional
show that pruning is needed practices
to maintain optimal plant
health.
Plants are dead, diseased or Determine the source of the
dying. problem: soils, hydrology, disease,
etc. Remedy the problem and
replace plants. Provide a one-time
fertilizer application to establish the
ground cover if a soil test indicates
it is necessary.
Weeds are present. Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the plants rather than spraying.
The main treatment area Sediment has accumulated to Search for the source of the
a depth greater than the sediment and remedy the problem if
original design sediment possible. Remove the sediment and
storage depth. dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Algal growth covers over Consult a professional to remove
50% of the area. and control the algal growth.
Cattails, phragmites or other Remove the plants by wiping them
invasive plants cover 50% of with pesticide (do not spray).
the basin surface.
Form SW401-Wet Detention Basin O&M-Rev.3 Page 2 Of 4
Permit Number:
(to be provided by DWQ)
Drainage Area Number:
BMP element: Potential problem: How I will remediate the problem:
The embankment Shrubs have started to grow Remove shrubs immediately.
on the embankment.
Evidence of muskrat or Use traps to remove muskrats and
beaver activity is present. consult a professional to remove
beavers.
A tree has started to grow on Consult a dam safety specialist to
the embankment. remove the tree.
An annual inspection by an Make all needed repairs.
appropriate professional
shows that the embankment
needs repair.
The outlet device Clogging has occurred. Clean out the outlet device. Dispose
of the sediment off-site.
The outlet device is damaged Repair or replace the outlet device.
The receiving water Erosion or other signs of Contact the local NC Division of
damage have occurred at the Water Quality Regional Office, or
outlet. the 401 Oversight Unit at 919-733-
1786.
The measuring device used to determine the sediment elevation shall be such
that it will give an accurate depth reading and not readily penetrate into
accumulated sediments.
When the permanent pool depth reads 6.5 feet in the main pond, the sediment
shall be removed.
When the permanent pool depth reads 3.5 feet in the forebay, the sediment
shall be removed.
BASIN DIAGRAM
(fill in the blanks)
Sediment Removal
Bottom
Permanent Pool Elevation 67.2'
63.7 Pe anen?
--------------- I—/ Volume
62.7 -ft Min.
Sediment
Storage
FOREBAY
Pool
-----Sediment Removal Elevation 607
----------- Volume
Bottom Elevation 59.7' I 1-ft 1W
MAIN POND
Storage
Form SW401-Wet Detention Basin O&M-Rev.3 Page 3 of 4
' Permit Number:
(to be provided by DWQ)
I acknowledge and agree by my signature below that I am responsible for the
performance of the maintenance procedures listed above. I agree to notify DWQ of any
problems with the system or prior to any changes to the system or responsible party.
Project name:Martin County Airport - Parallel Taxiway and Taxilane
BMP drainage area number: Area 2 - Pond
Print name: Russell Overman
Title: County Manager Martin County
Address: Post Office Box 668, Williamston, North Carolina 27892-0668
Phone: (252) 7 24? -1%cA`(3oO
Signature: % `?^ gQ, ?
Date: SI iS/o
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, lip , a Notary Public for the State of
N` ?, tr ?L[ fp^ l I tit , County of mck r-}1 n , do hereby certify that
W , ?Russelk aKman personally appeared before me this
day of , goo% , and acknowledge the due execution of the
forgoing ym? detention basin maintenance requirements. Witness my hand and official
se
:f
? ti} ? >?rue!?eet
ms, y pj.?.
ter' CA
SEAL
My commission expires
Form SW401-Wet Detention Basin O&M-Rev.3 Page 4 of 4
Permit No.
(o be provided by DWQ)
# Vto v Oa?F W A TF9pG
h r
NCDENR °
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form must be filled out, printed and submitted.
The Required Items Checklist (Part III) must be printed, filled out and submitted along with all of the required information.
PROJECT INFORMATION
Project name Martin County Airport - T-Hangar Taxilane Construction
Contact person Jason L. Elliott, El
Phone number [phone]
Date 8-May-08
Drainage area number Drainage Areas 14
II. DESIGN INFORMATION
Site Characteristics
Drainage area 184,529.00 ft2
Impervious area 102,480.00 ftz
% impervious 55.54 %
Design rainfall depth 1.00 in
Storage Volume: Non-SR Waters
Minimum volume required 8,388.00 ft3
Volume provided 8,944.00 ft3
Storage Volume: SR Waters
1-yr, 24-hr runoff depth in
Pre-development 1-yr, 24-hr runoff ff3
Post-development 1-yr, 24-hr runoff _ ft3
Minimum volume required ft3
Volume provided ft3
Peak Flow Calculations
?
f
1-yr, 24-hr rainfall depth 3.11 in ${ t(?B
t
` " ?'

Rational C, pre-development
016
(unitless) s
Rational C, post-development 0.59 (unitless) MAY 2 0 2008
Rainfall intensity: 1-yr, 24-hr storm 0.13 in/hr
Pre-development 1-yr, 24-hr peak flow 0.09 ft3/sec DENR - WATER OUAU i r
WETLANDS AND STORMWATER BRANCH
Post-development 1-yr, 24-hr peak flow 0.33 ft3/sec
Pre/Post 1-yr, 24-hr peak flow control 0.24 ft3/sec
Basin Elevations
Basin bottom elevation 59.70 ft
Sediment cleanout elevation 60.70 ft
Bottom of shelf elevation 66.70 ft
Permanent pool elevation 67.20 ft
SHWT elevation 68.0 (approx.) ft
Top of shelf elevation 67.70 It
Temporary pool elevation 68.00 It
Form SW401-Wet Detention Basin-Rev.4 Parts I. & II. Design Summary, Page 1 of 2
Permit
(to be provided by DWQ)
11. RESIGN INFORMATION
Volume and Surface Area Calculations
SA/DA ratio 4.60 (unitless)
Surface area at the bottom of shelf 7,930.00 ftz
Volume at the bottom of shelf 25,757.00 ft3
Permanent pool, surface area required 8,734.00 ft2
Permanent pool, surface area provided 9,624.00 ft2 OK
Permanent pool volume 28,927.00 ft3
Average depth for SA/DA tables 3.01 ft OK
Surface area at the top of shelf 11,788.00 ft2
Volume at the top of shelf 35,483.00 ft3
Forebay volume 5,756.00 ft3
Forebay % of permanent pool volume 19.90 % OK
Temporary pool, surface area provided 12,212.00 ft2
Drawdown Calculations
Treatment volume drawdown time 3.40 days OK
Treatment volume discharge rate 003 ft3ls
Pre-development 1-yr, 24-hr discharge 0.09 ft3/s OK
Post-development 1-yr, 24-hr discharge 0.12 ft3/s Decrease discharge rate
Additional Information
Diameter of orifice 1.5 in
Design TSS removal 85 %
Basin side slopes 3.00 :1 OK
Vegetated shelf slope 10.00 :1 OK
Vegetated shelf width 10.00 ft OK
Length of flowpath to width ratio 2.50 :1 Too short, increase ratio to at least 3:1
Length to width ratio 1;90 :1 OK
Trash rack for overflow & orifice? Y (Y or N) OK
Freeboard provided 1.50 ft OK
Vegetated filter provided? N (Y or N) Design must be based on 90% TSS removal
Recorded drainage easement provided? NIA (Y or N) OK
Capures all runoff at ultimate build-out? Y (Y or N) OK
Drain mechanism for maintenance or emergencies Pump Out
Form SW401-Wet Detention Basin-Rev.4 Parts I. & II. Design Summary, Page 2 of 2
Permit No
(to be provided by DWQ)
III. `REQUIRED ITEMS CHECKLIST
Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will
result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to
indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a
requirement has not been met, attach justification.
Pagel Plan
Initials Sheet No.
- a-.;Z 1. Plans (1" - 50' or larger) of the entire site showing:
Design at ultimate build-out,
Off-site drainage (if applicable),
Delineated drainage basins (include Rational C coefficient per basin),
Basin dimensions,
- Pretreatment system,
High flow bypass system,
- Maintenance access,
Proposed drainage easement and public right of way (ROAN),
Overflow device, and
- Boundaries of drainage easement.
v 2. Partial plan (1" = 30' or larger) and details for the wet detention basin showing:
Outlet structure with trash rack or similar,
- Maintenance access,
- Permanent pool dimensions,
- Forebay and main pond with hardened emergency spillway,
- Basin cross-section,
Vegetation specification for planting shelf, and
Filter strip.
3. Section view of the dry detention basin (1" = 20' or larger) showing:
- Side slopes, 3:1 or lower,
- Pretreatment and treatment areas, and
- Inlet and outlet structures.
G Q'2 4. If the basin is used for sediment and erosion control during construction, clean out of the basin is specified
on the plans prior to use as a wet detention basin.
5. A table of elevations, areas, incremental volumes & accumulated volumes for overall pond and for forebay,
to verify volume provided.
6. A construction sequence that shows how the wet detention basin will be protected from sediment until the
entire drainage area is stabilized.
7. The supporting calculations.
8. A copy of the signed and notarized operation and maintenance (0&M) agreement.
9. A copy of the deed restrictions (if required).
10. A soils report that is based upon an actual field investigation, soil borings, and infiltration tests. County
soil maps are not an acceptable source of soils information.
Form SW401-Wet Detention Basin-Rev.4 Part III. Required Items Checklist, Page 1 of 1
JUSTIFICATION FOR NOT USING VEGETATIVE FILTER STRIP
Despite being designed for 85% TSS removal, the pond outlet system does not include a
Filter Strip. The main reason for this is that the site is just too flat to be able to release the
water high enough. The only option was to release the outflow directly into the
downstream ditch. The ditch, however, should be an adequate substitution for the extra
stormwater treatment required. The outlet pipe is released into a new 650 ft long v-ditch
with a 0.15% longitudinal slope and 3:1 side slopes. During the 2-yr storm, the velocity
in this ditch is 1.48 fps. The new ditch connects to an existing v-ditch w/ 5:1 side slopes
and a similarly flat longitudinal slope. The water will travel 175 ft down this existing
ditch to where it will connect to the existing ditch running parallel to the runway.
Martin County Airport May 2008

401 WATER QUALITY CERTIFICATION
FOR
TAXILANE DEVELOPMENT
AT
MARTIN COUNTY AIRPORT
PROJECT DESCRIPTION AND PURPOSE
Due to an increasing general aviation and corporate presence at Martin County Airport,
additional hangar space is needed to meet the current and future needs of Airport users. The
Airport is preparing to begin two projects which will address needs associated with ongoing and
future growth.
The first project is the addition of Taxiway A, which is a parallel taxiway southwest of the
existing terminal and apron. The second project is the initial phase of the proposed Hangar Area
Development. The Taxiway A project is considered a Low-Impact Development and should not
require the use of a BMP for stormwater treatment purposes. The Hangar Area Development is
considered a High-Impact Development that will impact forested wetlands. This project is
required to go through the Section 401 / 404 permitting process.
EXISTING CONDITIONS
This project, located in Williamston, North Carolina, lies within the Tar-Pamlico River Basin.
The unnamed tributaries within the project site lead to the Huskanaw Swamp and eventually to
the Tar River. The Huskanaw Swamp is considered a class C waterway, with supplemental
classifications as NSW (nutrient sensitive waters), and Sw (swamp waters).
PROPOSED DEVELOPMENT
The proposed Hangar Area Development has been divided into two phases. The initial phase of
this project is the addition of three taxilanes to be used for access to the t-hangar building, which
is to be constructed on the site. The second phase would consist of the construction of two
corporate hangars, a paved apron, parking, and access roads.
The current phase of development for the Hangar Area will include 28,650 square feet of new
impervious area. An additional 28,016 square feet of impervious area will be added upon the
construction of the t-hangar building. Stage 2 of development in this area will add 42,614 square
feet of impervious area. Upon completion of both stages of development, 99,280 square feet (2.3
Acres) of impervious area will be added, draining to the proposed wet detention pond.
SOILS INFORMATION
A subsurface exploration was performed on the project site in November, 2006. The soil on the
site consisted of inter-layered coastal plain deposits of sands (SM, SC) and clays (CL). A water
table elevation was not established during the exploration. It was, however, noted that
groundwater was observed in existing drainage ditches at approximately 1 to 3 feet below the
ground surface.
Martin County Airport 1 May, 2008
I
STORMWATER QUALITY ANALYSIS
Much of the existing area is composed of wetlands and flat land. The majority of runoff is either
contained in low areas or exits through the existing ditch, which is located on the northwestern
side of the site. This ditch connects to the ditches that run parallel along the runway, through
which it eventually leaves the Airport property.
Due to the large percentage of new impervious area and the impacts to the existing wetlands, a
wet detention pond is being added to treat the first 1 inch of rainfall, in accordance with the
NCDENR Stormwater BMP Manual. The wet pond is being designed to remove 85% TSS. The
runoff which exceeds the 1 inch rainfall will bypass the pond through a new ditch which the
pond outlet will connect to. The ditch will then go around the hangar area and will be connected
to the existing ditch on the northwest edge of the site.
The temporary pool elevation is set at 0.8 feet above the permanent pool elevation. This
elevation provides a slightly larger volume than the required treatment volume of 8,388 cubic
feet. The actual volume of the temporary pool, at this elevation, will be 8,944 cubic feet.
The first 1 inch of rainfall will be detained by a diversion structure located in the new ditch, just
beyond the pond's inlet pipe. The diversion structure will consist of an earthen weir with a height
of 8 inches. The invert elevation of the ditch at the base of the weir is 67.35 feet. The crest of the
weir is designed to match the temporary pool elevation. Runoff will drain into the pond's forebay
through the 15 inch inlet pipe until the temporary pool is filled and will then begin to flow over
the diversion weir and through the ditch.
The stormwater will go from the forebay to the main pond via an earthen berm. The main pond
contains a riser structure and an emergency outlet with a concrete apron. The riser structure will
have a submerged orifice with a 1.5 inch opening, set to match the permanent pool elevation.
Runoff that exceeds this elevation will leave through the orifice. The orifice is designed to
release the full volume of the temporary pool over 3.4 days. The riser will have a rectangular
weir opening with a crest matching the temporary pool elevation. The weir opening will have a
height of 8 inches and a width of 4 feet. Flow from both the orifice and the weir will be
discharged from the structure through a 12 inch outlet pipe. The invert of the outlet pipe will be
equal to the permanent pool elevation.
Despite being designed for 85% TSS removal, the pond outlet system does not include a Filter
Strip. The main reason for this is that the site is just too flat to be able to release the water high
enough. The only option was to release the outflow directly into the downstream ditch. The
ditch, however, should be an adequate substitution for the extra stormwater treatment required.
The outlet pipe is released into a new 650 ft long ditch with a 0.15% longitudinal slope and 3:1
side slopes. During the 2-yr storm, the velocity in this ditch is 1.48 fps. The new ditch connects
to an existing ditch w/ 5:1 side slopes and a similarly flat longitudinal slope. The water will
travel 175 ft through this existing ditch to where it will connect to the existing ditch running
parallel to the runway.
Martin County Airport 2 May, 2008
DRAINAGE AREAS
DRAINAGE AREA PERVIOUS AREA IMPERVIOUS AR EA TOTAL AREA C CN TIME OF IMP %
EXISTING PROPOSED FUTURE TOTAL CONCENTRATION
SQ. FT ACRES SQ. FT. SQ. FT. SQ.FT. SQ. FT. ACRES SQ. FT ACRES HR MIN.
Drainage Area 1 16,438 0.38 3,200 9,654 33,037 45,891 1.05 62,329 1.43 0.74 90 0.1 6 74%
Drainage Area 2 16,329 0.37 0 47,012 3,104 50,116 1.15 66,445 1.53 0.75 92 0.1 6 75%
Drainage Area 3 5,249 0.12 0 0 677 677 0.02 5,926 0.14 0.24 77 0.083 5 11%
Drainage Area 4 42,681 0.98 0 0 7,148 7,148 0.16 49,829 1.14 0.26 77 0.1 6 14%
TOTALS = 80,697 1.85
3,200 56,666 43,966 103,832 2.38 184,529 4.24
56%
T-Hangar Taxilane Pond
Martin County Airport
May 2008
PIPE DATA, 2-YEAR STORM

Name

Shape
Diameter/Depth
inches

Len th feet
Conduit Slope
%
Upstream Invert
Elevation feet Downstream
Invert Elevation
feet

Ditch Side Slopes

Max Flow cfs
Max Velocity
ft/s
FP-2* Circular Pie 18 40 0.20 67.85 67.77 0 5.76 4.16

Ditch Below Taxilanes Trapezoidal Ditch
5' bottom
24
115
0.20
67.77
67.53
4:1
5.48
0.57
FP-3* Circular Pie 24 40 0.20 67.53 67.45 0 11.59 5.78

Ditch to Diversion Weir Trapezoidal Ditch
5' bottom
24
50
0.20
67.45
67.35
4:1
11.47
1.16
Bypass Ditch V-Ditch 24 135 0.18 68.00 67.10 3:1 5.48 1.48
P-3 Circular Pie 15 35 0.43 67.35 67.20 0 6.07 5.19
P-4 Circular Pie 12 47 0.21 67.20 67.10 0:00 -1.39 -1.72
Outlet Ditch V-Ditch 36 656 0.14 67.10 66.16 3:1 6.98 1.48
Orifice Area Orifice Invert Max Velocity
Name s .ft. Orifice Shape Orifice Type Elevation feet Max Flow cfs ft/s
Orifice from Wet Detention Pond to
Riser Structure 0.012 Circular Side Outlet 67.2 0.08 6.08

Name
Weir Type Weir Length
feet Weir Crest
Elevation feet Weir Crest Top
feet
Max Flow cfs Max Velocity
ftls
Diversion Weir Transverse weir 10 68 70.4 5.59 0.00
Weir from Forebay to Wet
Detention Pond
Transverse weir
20
66.7
67.2
7.63
0.00
Riser Weir Transverse weir 12 68 68.7 -1.29 0.00
Emergency Overflow Weir Transverse weir 28 70 71 0 0.00
* FP-2 and FP-3 are Future Pipes,
to be installed in Phase 2
Martin County Airport
T-Hangar Talilane Pond May 2008
PIPE DATA, 10-YEAR STORM

Name

Shape
Diameter/Depth
inches

Length feet
Conduit Slope
%
Upstream Invert
Elevation feet Downstream
Invert Elevation
feet

Ditch Side Slo es

Max Flow cfs
Max Velocity
ft/s
FP-2` Circular Pie 18 40 0.20 67.85 67.77 0 9.69 5.30

Ditch Below Taxilanes Trapezoidal Ditch
5' bottom
24
115
0.20
67.77
67.53
4:1
9.19
0.60
FP-3' Circular Pie 24 40 0.20 67.53 67.45 0 19.27 7.07

Ditch to Diversion Weir Trapezoidal Ditch
5' bottom
24
50
0.20
67.45
67.35
4:1
19.13
1.28
Bypass Ditch V-Ditch 24 135 0.18 68.00 67.10 3:1 11.1 1.80
P-3 Circular Pie 15 35 0.43 67.35 67.20 0 8.25 6.54
P-4 Circular Pie 12 47 0.21 67.20 67.10 0:00 -2.86 -3.63
Outlet Ditch V-Ditch 36 656 0.14 67.10 66.16 3:1 14.19 1.83
Orifice Area Orifice Invert Max Velocity
Name s .ft. Orifice Shape Orifice Type Elevation feet Max Flow cfs ft/s
Orifice from Wet Detention Pond to
Riser Structure 0.012 Circular Side Outlet 67.2 0.08 6.07

Name
Weir Type Weir Length
feet Weir Crest
Elevation feet Weir Crest Top
feet
Max Flow cfs Max Velocity
ft/s
Diversion Weir Transverse weir 10 68 70.4 11.34 0.00
Weir from Forebay to Wet
Detention Pond
Transverse weir
20
66.7
67.2
11.63
0.00
Riser Weir Transverse weir 12 68 68.7
_ -2.79 0.00

Emergency Overflow Weir
Transverse weir
28 I
70
71 t
0
0.00
" FP-2 and FP-3 are Future Pipes,
to be installed during Phase 2
Martin County Airport
T-Hangar Talilane Pond May 2008
CONICAL VOLUME METHOD
COMBINED (POND & FOREBAY)
Elevation (ft) Area (sq. ft.) Area (ac) Al+A2+SQRT(Al*A2) Volume (ac-ft) Sum (ac-ft) Acc. Vol. (cu. ft)
59.7 1,003 0.02 0.02 0.46
60.7 1,433 0.03 0.08 0.03 0.03 1,212
61.7 1,932 0.04 0.12 0.04 0.07 2,888
62.7 2,935 0.07 0.17 0.06 0.12 5,304
63.7 3,873 0.09 0.23 0.08 0.20 8,697
64.7 4,974 0.11 0.30 0.10 0.30 13,109
65.7 6,225 0.14 0.38 0.13 0.43 18,697
66.7 7,930 0.18 0.49 0.16 0.59 25,757
67.2 9,624 0.22 0.60 0.10 0.69 30,139
67.7 11,788 0.27 0.74 0.12 0.81 35,483
67.8 11,928 0.27 0.82 0.03 0.84 36,669
67.9 12,070 0.28 0.83 0.03 0.87 37,869
68.0 12,212 0.28 0.84 0.03 0.90 39,083
68.1 12,355 0.28 0.85 0.03 0.93 40,311
68.2 12498 0.29 0.86 0.03 0.95 41,554
68.7 13221 0.30 0.89 0.15 1.10 47,983
69.7 14730 0.34 0.96 0.32 1.42 61,951
* Volume = (1/3) * (Elev. 2 - Elev. 1) * [Al +A2 + SQRT (A1 * A2)
Permanent Pool Volume = 30,139 - 1,212 = 28,927 cf
Forbay Volume @ Permanent Pool Elevation = 5,756 cf (20% Permanent Pool Volume)
Avg. Depth of Permanent Pool = 28,927 cf / 9,624 sf = 3.0 ft
CONICAL VOLUME METHOD
FOREBAY
Elevation (ft) Area (sq. ft.) Area (ac) Al+A2+SQRT(A1*A2) Volume (ac-ft) Sum (ac-ft) Acc. Vol. (cu. ft)
62.7 435 0.01 0.01 0.21
63.7 738 0.02 0.04 0.01 0.01 580
64.7 1,114 0.03 0.06 0.02 0.03 1,499
65.7 1,561 0.04 0.09 0.03 0.06 2,831
66.7 2,080 0.05 0.12 0.04 0.11 4,645
67.2 2,366 0.05 0.15 0.03 0.13 5,756

CONICAL VOLUME METHOD
MAIN POND
Elevation (ft) Area (sq. ft.) Area (ac) Al+A2+SQRT(Al*A2) Volume (ac-ft) Sum (ac-ft) Acc. Vol. (cu. ft)
59.7 1,003 0.02 0.02
60.7 1,433 0.03 0.08 0.03 0.03 1,212
61.7 1,932 0.04 0.12 0.04 0.07 2,888
62.7 2,500 0.06 0.15 0.05 0.12 5,098
63.7 3,135 0.07 0.19 0.06 0.18 7,909
64.7 3,860 0.09 0.24 0.08 0.26 11,401
65.7 4,664 0.11 0.29 0.10 0.36 15,656
66.7 7,930 0.18 0.43 0.14 0.50 21,881
67.2 9,624 0.22 0.60 0.10 0.60 26,263
67.7 11,788 0.27 0.74 0.12 0.73 31,607
67.8 11,928 0.27 0.82 0.03 0.75 32,793
67.9 12,070 0.28 0.83 0.03 0.78 33,993
68.0 12,212 0.28 0.84 0.03 0.81 35,207
68.1 12,355 0.28 0.85 0.03 0.84 36,435
68.2 12,498 0.29 0.86 0.03 0.86 37,678
68.7 13,221 0.30 0.89 0.15 1.01 44,107
69.7 14,730 0.34 0.96 0.32 1.33 58,075
* Volume = (1/3) * (Elev. 2 - Elev. 1) * [Al +A2 + SQRT (Al * A2)
Permanent Pool Volume = 30,139 - 1,212 = 28,927 cf
Forbay Volume @ Permanent Pool Elevation = 5,756 cf (20% Permanent Pool Volume)
THE LPA GROUP OF NORTH CAROLINA, P.A.
5000 Falls of Neuse Road, Suite 304
Raleigh, North Carolina 27609
[phone]
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5000 Falls of Neuse Road, Suite 304
Raleigh, North Carolina 27609
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[Max Flow = 9.6862][Max Velocity = 5.30]
Upstream Elevation Downstream Elevation Flow
69.5
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Time
J J J J
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9PM 25 Fri 3AM 6AM 9AM 12PM
5.5
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[Max Flow = 9.1944] [Max Velocity = 0.60]
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[Max Flow= 19.2715] [Max Velocity = 7.07]
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24 Thu 3AM 6AM 9AM 12PM 3PM 6PM 9PM 25 Fri 3AM 6AM 9AM 12PM
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[Max Flow = 19.1337][Max Velocity = 1.28]
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24 Thu 3AM 6AM 9AM 12PM 3PM 6PM 9PM 25 Fri 3AM 6AM 9AM 12PM
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Pond - 10 yr
[Max Stage = 68.161 ]
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67.5
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[Max Flow = 14.1895][Max Velocity = 1.83]
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Apr 2008 Time
Pond - 50 yr
[Max Stage = 68.507]
68.4
68.2
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67.6
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24 Thu 3AM 6AM 9AM 12PM 3PM 6PM 9PM 25 Fri 3AM 6AM 9AM 12PM
Apr 2008 Time

November 17, 2006
S&ME
The LPA Group of North Carolina, P.A.
4904 Professional Court, Suite 201
Raleigh, North Carolina 27609
Attention: Mr. Terry Bumpus
J
Reference: Subsurface Exploration Report
Proposed Corporate Apron and Taxiway
Martin County Airport
Williamston, North Carolina
S&ME Project No. 1051-06-365
Dear Mr. Bumpus:
S&ME, Inc. is pleased to submit this report of the subsurface exploration conducted for the
referenced project. Work was conducted in accordance with S&ME's Revised Proposal P059-06E
3rd Revision dated June 21, 2006. The purpose of the exploration was to evaluate subsurface
conditions as they relate to site grading and pavement subgrade support for the proposed corporate
apron and taxiway. This report presents a summary of pertinent project information, a description of
our exploration program, and results of field testing. A Boring Location Plan, Generalized
Subsurface Profile, and Test Boring Records are included in the Appendix.
PROJECT AND SITE DESCRIPTION
A Corporate Apron and Taxiway are planned for the Martin County Airport located in Williamston,
North Carolina. The proposed taxiway will be approximately 1,200 feet long and constructed south
of the existing apron and taxiway. The proposed Corporate Apron portion of the project will consist
of two taxiways constructed to the east of the existing apron.
l
S&ME, INC. / 3201 Spring Forest Road / Raleigh, NC 27616 / p 919.872.2660 f 919.876.3958 / www.smeinc.com
Subsurface. Exploration Report S&ME Project No. 1051-06-365
Proposed Corporate Apron and Taxiway November 17, 2006
' Martin County Airport
Williamston, North Carolina
• Based on our site reconnaissance, the site is relatively flat with drainage ditches along the runway
and tree line on the northeastern portion of the site. The site is mostly open with pine trees in the
vicinity of the proposed Corporate Apron. An access road runs along the proposed taxiway. The
existing apron and access road are paved with asphalt.
J
EXPLORATION PROGRAM
The exploration program for this project included the performance of 9 soil test borings. Soil test
J borings were advanced to an approximate depth of 10 feet beneath existing ground surface. The
J boring locations were selected by The LPA Group of North Carolina and were located in the field
J by a representative of S&ME by estimating distances from existing site features. Two of the
J provided boring locations (B-8 and B-9) were moved out of the woods since clearing was not
allowed. The approximate boring locations are shown on Figure 1 in the Appendix.
The soil borings were advanced using hollow stem auger drilling procedures with a CME-45-06
drill rig. Within each of the soil test borings, samples of subsurface soils were obtained at
approximately 2-1/2 foot intervals to a depth of 10 feet using a split-spoon sampler. Standard
penetration tests were conducted in conjunction with split-spoon sampling in general accordance
7 with ASTM D 1586.
The boreholes were observed for groundwater at completion of drilling. Boreholes were then
backfilled up to the original ground surface with auger cuttings. Boreholes performed in pavement
areas were patched with cold patch asphalt.
A Generalized Subsurface Profile drawing (Figure 2) and Test Boring Records presenting
subsurface information from the borings are included in the Appendix. Stratification lines shown on
the Test Boring Records are intended to represent approximate depths of changes in soil types.
Naturally, transitional changes in soil types are often gradual and cannot be defined at a particular
depth.

t
J

1
l
1

a
a
Subsurface Exploration Report
Proposed Corporate Apron and Taxiway
Martin County Airport
Williamston, North Carolina
SUBSURFACE CONDITIONS
S&ME Project No. 1051-06-365
November 17, 2006
Borings B-2, B-4, and B-6 were performed in asphalt paved areas. Approximately 3 to 5 inches of
asphalt and 5 inches of aggregate base course (ABC) stone were encountered at the ground surface.
Topsoil was encountered at the ground surface in the remaining borings. Topsoil thickness ranged
from approximately 6 to 12 inches.
The typical subsurface profile below the pavement sections and topsoil consists of interlayered
coastal plain deposits of sands (SM, SC) and clays (CL, CH). SPT N-values within natural soils
ranged from 4 to 23 blows per foot. N-values indicate soft to stiff consistencies for clays and loose
to medium dense relative densities for sands. Natural soils appeared moist to wet.
Groundwater was not observed in any of the boreholes at the termination of drilling operations.
However, groundwater was observed in the drainage ditches approximately 1 to 3 feet below the
existing ground surface. Groundwater elevations can be expected to fluctuate due to seasonal
variations in rainfall, evaporation, and other factors.
LABORATORY TESTING
Laboratory testing consisted of natural moisture content, grain size analysis, Atterberg limits,
standard Proctor, and California bearing ratio (CBR) testing. Grain size analysis testing was
performed on a split-spoon sample obtained from boring B-3 at an approximate depth of 1 foot.
Testing indicates the sample contained mostly fine sand (73 percent) with 24 percent fines (silt and
clay).
Atterberg limits testing were performed on a split-spoon sample obtained from boring B-7 at an
approximate depth of 1 foot. Atterberg limits testing indicated a liquid limit of 28 percent and
plasticity index of 9 percent. These values indicate the sample was a low plasticity clay with USCS
classification of CL.
3
Subsurface Exploration Report S&ME Project No. 1051-06-365
Proposed Corporate Apron and Taxiway November 17, 2006
Martin County Airport
Williamston, North Carolina
A standard Proctor test was performed on the bulk sample of near surface soils obtained from
boring B-3. Testing indicates a maximum dry density of about 120 pounds per cubic foot with an
optimum moisture content of about 13.1 percent. Natural moisture content tests performed on near
surface soils-indicated moisture contents ranging from 8.7 to 21.3 percent.
A California bearing ratio (CBR) test was also performed on the recompacted bulk sample of the
soils obtained from boring B-3 from an approximate depth of 1 to 5 feet. The test specimen was
recompacted to approximately 98 percent of the standard Proctor maximum dry density neat the
optimum moisture content. The test specimen was then soaked. A California bearing ratio of 6.4
percent was measured. Based on the laboratory testing it is our recommendation that a CBR value
of 6 percent be used for the design of the corporate apron and taxiway. Subgrade soils should be
reworked and compacted to at least 98 percent of the standard Proctor maximum dry density within
plus or minus 3 percent of the optimum moisture content.
CONCLUSIONS AND RECOMMENDATIONS
If
The subsurface exploration indicates that the site is adaptable for the proposed construction
site grading does not occur during hot and dry conditions, some repair of moisture sensitive near
surface soils should be expected. The following paragraphs present more detailed conclusions
and recommendations regarding site development.
Site Preparation
Site grading will be difficult during wet periods of the year. Most near surface soils are moisture
sensitive, and when wet, will tend to rut and pump under rubber-tired traffic and provide poor
subgrade support for structures and pavements. To reduce potential earthwork problems, we
recommend that site preparation and grading be conducted during the typically drier summer
months, if possible. If grading is attempted during wet conditions, more extensive repair of near
surface soils and possible use of select off-site borrow will be necessary to adequately prepare
subgrades for new construction. Heavy rubber-tired construction equipment should not be allowed
4
Subsurface Exploration Report S&ME Project No. 1051-06-365
Proposed Corporate Apron and Taxiway November 17, 2006
Martin County Airport
Williamston, North Carolina
to operate on exposed subgrades during wet conditions. Even during drier periods of the year, we
recommend that exposed subgrades be sloped and sealed at the end of each day to promote runoff
and reduce infiltration from rainfall.
Site preparation should begin with clearing of all trees, vegetation, topsoil, existing asphalt, and
other unsuitable surface materials. The existing ABC stone may remain in place provided it is stable
during proofroll. However, the existing ABC stone should not be included as part of the new
pavement section. Approximately 6 to 12 inches of topsoil/rootmat was encountered in borings.
Deeper stripping depths are usually required to remove rootmat from areas with trees. The depth of
topsoil stripping will also depend on prevailing weather conditions at time of construction. During
wet conditions, rubber-tired equipment will mix topsoil with underlying "clean" soils, causing
stripping depths to be greater than topsoil depths indicated on borings. As such, actual stripping
depths could be greater than topsoil/rootmat thicknesses encountered. Topsoil may be stockpiled
on site and reused in landscaped areas. Topsoil should not be used for construction of permanent
slopes.
Following stripping, areas at planned grades and areas that will receive fill should be proofrolied
with a loaded tandem axle dump truck or equivalent. Any areas that are observed to rut, pump, or
deflect excessively during the proofrolling process should be repaired as recommended by the
geotechnical engineer. It is anticipated that some repairs will be required in the area of borings B-1,
B-7, B-8 and B-9. Possible repair measures may include undercutting to stable soils and backfilling
with well compacted, low-plasticity materials, discing/drying/compacting existing soils, placement
of a geotextile stabilization fabric and crushed stone, or some combination of these. The most
practical repair measure will be influenced by the degree of instability which exists and weather
conditions. As such, actual repair measures must be determined in the field at time of construction.
I Excavations
Based on results of borings, low to moderate consistency soils are present at the site. Past
experience indicates that these materials can be excavated by routine earth-moving equipment. That

*11
Subsurface Exploration Report S&ME Project No. 1051-06-365
Proposed Corporate Apron and Taxiway November 17, 2006
Martin County Airport
.
Williamston, North Carolina
is, mass excavation can be accomplished by bulldozer-pushed scrapers with light to moderate
preloosening of higher consistency soils by tractor-drawn rippers. A moderately heavy front-end
loader should be able to excavate these materials operating basically unassisted. Local excavations
for shallow utility trenches and foundations within soils and fill can likely be accomplished by a
conventional backhoe.
For confined excavations, trench safety must be evaluated on a case-by-case basis. The contractor
will be responsible for all site safety, including the determination of appropriate trench safety
measures according to OSHA guidelines.
Structural Fill
The soils at this site having a Unified Soil Classification designation of CL, ML, SC, and SM are
suitable for reuse as structural fill provided that the moisture content is properly controlled
during placement and compaction. The moisture condition of near surface soils will be influenced
by prevailing weather conditions. At the time our borings were performed, some of the near surface
soils were wet and would require some drying prior to use as fill.
All structural soil fill should consist of low plasticity soil (PI<30), be free of debris and have less
than 5 percent organics. Fill should be placed in 8 to 10 inch loose lifts and compacted to at least
95 percent of the standard Proctor maximum dry density (ASTM D 698) and within three percent of
the optimum moisture content. Fill within 18 inches of finished subgrade should be compacted to at
least 98 percent of the standard Proctor maximum dry density. In-place testing should be performed
during fill placement to confirm that the recommended degree of compaction is achieved.
QUALIFICATIONS OF REPORT
This report has been prepared in accordance with generally accepted engineering practice for
specific application to this project. Any wetland, environmental, or contaminant assessment efforts
are beyond the scope of this geotechnical exploration; and therefore, those issues are not addressed
1 ? ? 6
Subsurface Exploration Report S&ME Project No. 1051-06-365
Proposed Corporate Apron and Taxiway November 17, 2006
Martin County Airport
Williamston, North Carolina
in this geotechnical exploration report. The recommendations contained in this report are based on
the applicable standards of our profession at the time this report was prepared. No other warranty,
express or implied, is made.
Conclusions and recommendations submitted in this report are based, in part, upon the data
obtained from the geotechnical exploration. The nature and extent of variations between and
outside of the borings may not become evident until construction. If variations appear evident, then
it will be necessary to re-evaluate the recommendations of this report. In the event that any changes
in the grades, nature, design, or location of the proposed building or pavements are planned, the
recommendations contained in this report should be reviewed and modified or verified in writing.
We recommend that our firm be provided the opportunity for general review of final design
specifications to confirm that our recommendations are properly interpreted and implemented.
CLOSURE
S&ME, Inc. appreciates the opportunity to provide our professional engineering services on this
project. Should you have any questions concerning this report or if we may be of further assistance,
please contact us at your convenience.
Sincerely,
S&ME, Inc.
/? efF,r 3 ?8gy
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J. Adam Browning, E.I. Abner F. 4Riggsif".' P
Staff Professional Senior Geotechnial guiX 15, 5
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N.C. Registration No.1,415 o
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Attachments 4;(
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.....

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.1.2.....

......

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.

.8........
.
......

.....
.....

...::

.8........
..........

.....
.....

7......
.........

......
......

7..........................
...............................
..... ...... . ... .......... ...... ..
..
...................... .........
7 ........ ..........
7 ....... ...........
7 ....... .. ...........
9 ....... .. ......
14 .........
9 ...... ... ..........
13 ..... .. .........
. 6 ....... ...............................
8

Topsoil 0 Gravel
Silty Sand Clayey Sand
Silty Clay Sandy Clay
Asphalt
N = Standard Penetration Test resistance value (blows per foot). The depicted stratigraphy is shown for illustrative purposes only. The actual subsurface conditions will vary between boring locations.
SCALE: N.T.S. GENERALIZED SUBSURFACE CONDITIONS FIGUF
Forest Road
3201 S
rin
p
g NO.
CHECKED BY: JAB Raleigh, INC 27616

S&ME
Martin Co.Airport Taxiway
DATE: 11116/2006 - [phone] 2
[phone] fax North Carolina
Williamston
JOB NO: 1051-06-365 ENV RNONMENTTALSERVICES www•smeinc.com ,