20151229 Ver 1_401 Water Quality Certification Report_20151130

401 WATER QUALITY
CERTIFICATION REPORT
HAECO FACILITY IMPROVEMENTS PROJECT
Submitted on Behalf of.•
Piedmont -Triad International Airport
Prepared by:
WK Dickson & Co., Inc.
720 Corporate Center Drive
Raleigh, North Carolina 27607
November 2015

Table of Contents
1. Introduction.......................................................................................................................1-1
1.1. Project Description.....................................................................................................1-1
2. Hydrology and Hydraulics..............................................................................................
2-1
2.1. Methodology..............................................................................................................2-1
2.2. Hydrology...................................................................................................................
2-1
2.2.1 Drainage Areas.................................................................................................
2-1
2.2.2 Rainfall...............................................................................................................2-2
2.2.3 Land Use............................................................................................................
2-2
2.2.4 Hydrograph Translation.................................................................................
2-2
2.2.5 NRCS Curve Numbers....................................................................................
2-3
2.2.6 Channel/Storage Routing................................................................................
2-4
2.2.7 Summary of Hydrologic Results....................................................................2-4
2.3. Hydraulics..................................................................................................................2-4
2.3.1 Energy Loss Coefficients.................................................................................2-5
2.3.2 Starting Water Surface Elevation...................................................................2-5
2.3.3 Model Run Descriptions.................................................................................
2-5
2.3.4 Hydraulic Evaluation of Radar Road............................................................2-5
2.3.5 Evaluation of Downstream Flooding............................................................
2-6
2.3.6 Closed Drainage Systems...............................................................................
2-7
2.3.7 Outfall Protection for Closed Drainage System ..........................................
2-7
3. Water Quality Compliance............................................................................................. 3-1
3.1. Overview..................................................................................................................... 3-1
2.3.1 Proposed Impervious Areas...........................................................................3-1
2.3.2 High Flow Rate Bioretention Pond Design Criteria .................................... 3-2
2.3.3 Water Quality Volume (WQV)...................................................................... 3-2
2.3.4 Pond Design Summary................................................................................... 3-3
3.2. Conclusion...................................................................................................................3-6
HAECO Facility Improvements Project Page i
Stormwater Report

Tables
Table 1: Summary of Area Required for Treatment............................................................1-1
Table 2: Summary of Water Quality Treatment Credits.....................................................1-2
Proposed Concept Plan
Table 3: Design Storm Rainfall Depths..................................................................................
2-2
Table 4: Summary of Hydrologic Input Data.......................................................................
2-3
Table 5: Comparison of Peak Flows at Radar Road.............................................................
2-4
Table 6: Energy Loss Coefficients...........................................................................................
2-5
Table 7: Bend Loss Coefficients..............................................................................................
2-5
Table 8: Culvert Performance for at Radar Road.................................................................
2-6
Table 9: Hydraulic Summary of Harris Teeter Open Channel ..........................................
2-6
Table 10: Minimum Area of Impervious Cover Required for Treatment .........................
3-1
Table 11: Proposed Impervious Cover to SCM....................................................................
3-1
Table 12: Calculated Storage Volumes..................................................................................
3-2
Table 13: Water Surface Elevations at Proposed Pond ........................................................
3-3
Table 14: Summary of Flow Splitter Design.........................................................................
3-4
Table 15: Flow Splitter Performance......................................................................................
3-4
Appendices
Appendix A
Proposed Concept Plan
Appendix B
Input Data for SWMM
Appendix C
Existing and Proposed Conditions Drainage Area Maps
Appendix D
Existing and Proposed Conditions Land Use Mapping
Appendix E
CD with Digital Copy of EPA SWMM Models
Appendix F
Outlet Protection Calculation
Appendix G
Water Quality Calculation and Stage -Storage Relationship for SCM
Appendix H
Anti -Floatation Calculation for Riser
Appendix I
Detention Time Calculation
Appendix J
Maintenance and Operation Plan
HAECO Facility Improvements Project Page ii
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Section 1: Introduction
1.1 Project Description
This report supports the design of the stormwater control measures (SCMs) needed to
develop the HAECO Facility Improvements project at the Piedmont Triad International
Airport in compliance with the North Carolina Department of Environmental Quality
(NCDEQ) regulatory requirements for new development at an airport. A 0.8 -acre high
flow rate bioretention pond is being proposed to meet the regulatory water quality
requirements for NCDEQ. This bioretention pond was designed to infiltrate runoff
generated from the 1St inch of rainfall at a relatively high rate to satisfy the water quality
requirements outlined in Session Law 2012-200. As shown in the concept plans
included in Appendix A, the airport is proposing a 15.9 -acre site development project
including the construction of the following:
♦ 5.06 acres of new impervious area associated with the proposed HAECO hangar;
♦ 5.51 acres of new impervious area associated with the proposed HAECO apron;
♦ 0.32 acres of new impervious area associated with the proposed HAECO fire
lanes flanking the proposed hangar;
♦ 0.09 acres of new impervious area associated with the proposed HAECO
sidewalks;
♦ Removal of an existing fire suppression pond;
♦ Removal of an existing 1.1 -acre wet pond being used for detention and water
quality; and
♦ Construction of a new 0.7 -acre high flow rate bioretention pond that will result in
infiltration of the water quality rainfall event.
In addition to providing treatment for the proposed new impervious areas associated
with the HAECO Facility Improvements project, the SCM will replace the treatment
being provided by an existing wet pond located on the eastern side of the site. This
existing wet pond has a contributing drainage area of 15.29 acres with 14.04 acres of
impervious cover. In total, the proposed SCM will need to provide treatment for 24.61
acres of impervious cover as shown in the following table:
Table 1: Summary of Area Required for Treatment
Location
Proposed Hangar
Proposed Apron
Proposed Access Route
Proposed Sidewalk
Existing HAECO Site (Wet Pond)
HAECO Facility Improvements Project
Stormwater Report
Impervious Cover (acres)
5.06
5.11
0.32
0.09
14.03
TOTAL = 24.61 acres
Page 1-1

Section 1: Introduction
As outlined in this report, the proposed SCM will provide water quality treatment for a
total of 44.52 acres of impervious cover which exceeds the minimum required for
treatment (24.61 acres). As a result, the airport is formally requesting water quality
treatment credits to offset a site development project in the future with up to 19.91 acres
of impervious surface. The following table summarizes the water quality treatment
credits being requested:
Table 2: Summary of Water Quality Treatment Credits
Description Impervious Area (acres)
Required Area for Treatment 24.61
Provided Area for Treatment 44.52
DIFFERENCE = 19.91 acres
Also provided in this report is an evaluation of downstream flooding resulting from the
proposed site changes. The analysis showed that the proposed project will cause
increases to peak flows downstream but will not flood insurable structures, roads, or
cause damage to existing property or the existing Harris Teeter detention pond.
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Section 2: Hydrology and Hydraulics
2.1 Methodology
The Environmental Protection Agency (EPA) Storm Water Management Model 5.0
(SWMM) was used to size the proposed collection system, flow splitters, and
bioretention pond with riser. SWMM simulates the surface runoff response to
precipitation for an interconnected system of surfaces, channels, closed pipe systems,
culverts, flow splitters, and ponds. SWMM is an ideal model for a complex drainage
system such as the one seen at the HAECO site as it combines hydrology and hydraulics
and allows the user to not only size on-site improvements but also evaluate downstream
flooding. Combining hydrology and hydraulics eliminates the need to iterate between a
hydrologic model and a hydraulic model which eliminates the potential for errors.
2.2 Hydrology
Input data for the model was developed using topographic, landuse, and soils maps in
GIS to delineate and calculate the basin areas, percent impervious, and Natural
Resources Conservation Service (NRCS) hydrologic parameters. The precipitation data
for the 24-hour duration, Type II storm was used to represent the synthetic rainfall
event. SWMM estimates surface runoff for a sub -basin based on percent impervious,
basin width, basin slope, and NRCS curve number for the unconnected pervious areas.
A copy of the SWMM input values for the existing and proposed conditions is provided
in Appendix B. Unit hydrographs are translated using the watershed basin and slope
parameters. This is unique to SWMM.
2.2.1 Drainage Areas
Drainage area maps for the existing and proposed conditions have been included with
this report in Appendix C. Drainage areas were delineated using the following
topography:
♦ 2 -foot contour interval existing conditions topographic mapping from Guildford
County GIS;
♦ 1 -foot contour interval topographic mapping provided by Michael Baker &
Associates titled "ADP Mapping (May 2014).dwg";
♦ Inventory mapping of pipes and catch basins provided by Michael Baker &
Associates titled "ADP Mapping (May 2014).dwg"; and
♦ 1 -foot contour interval proposed conditions topographic mapping generated by
WK Dickson.
2.2.2 Rainfall
Rainfall distributions for the SWMM model were derived using the NRCS Type II
standard distribution. Total rainfall depths for the modeled frequency storms were
HAECO Facility Improvements Project Page 2-1
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Section 2: Hydrology and Hydraulics
obtained online from the NOAA's Nation Weather Service website. Table 3 shows the
total rainfall depths used for this study.
Table 3: Design Storm Rainfall Depths
Design Storm
Rainfall Depth (in)
2 -year, 24-hour
3.31
10 -year, 24-hour
4.77
25 -year, 24-hour
5.65
50 -year, 24-hour
6.35
100 -year, 24-hour
7.07
Source: NOAA's Nation Weather Service website
2.2.3 Land Use
Land use is the watershed cover condition as it relates to the actual type of development
within the watershed. Land use influences the runoff characteristics of a sub -basin, and
combined with other basin characteristics is used to determine the percent impervious
and NRCS curve number for the basin. Appendix D shows the existing and proposed
conditions land use mapping for this project. Input data for the existing and proposed
percent impervious values is found in Table 4.
2.2.4 Hydrograph Translation
NRCS methodologies typically use a time of concentration parameter to help calculate
the response of the watershed to rainfall. SWMM uses watershed basin width and slope
parameters to create the unit hydrograph used in the model that will translate the
rainfall into runoff. The watershed width is a parameter unique to SWMM that helps
define the watershed shape by taking the watershed area and dividing it by the length of
the longest flow path. Additionally, SWMM requires input of a basin slope in the
calculations used to translate the hydrograph. The basin slope is the maximum grade
change from the upstream end of the watershed to the downstream end divided by the
length of the longest flow path. The sub -basin slopes and widths are included in Table 4.
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Section 2: Hydrology and Hydraulics
Table 4: Summary of Hydrologic Input Data
2.2.5 NRCS Curve Numbers
The NRCS curve number approach was used in computing the runoff response in
SWMM. Runoff curve numbers (RCNs) were generated for the pervious areas of the
sub -basins using the NRCS document entitled Urban Hydrology for Small Watersheds,
dated June 1986 and commonly referred to as TR -55. This method relates the drainage
characteristics of soil group, land use category, and antecedent moisture conditions to
assign a runoff curve number. The runoff curve number and an estimate of the initial
surface moisture storage capacity are used to calculate a total runoff depth for a storm in
HAECO Facility Improvements Project Page 2-3
Stormwater Report
Existing/
Existing
Proposed
Proposed
Proposed
Drainage
Drainage
Proposed
Percent
Percent
Basin
Basin
Basin
Area
Pervious
Impervious
Impervious
Slope
Width
ID
(acre)
RCN
(M
M
M
(feet)
10
77.1
74
31%
31%
0.6%
1019
20
28.8
74
34%
34%
0.8%
995
30
19.3
74
40%
40%
1.0%
454
40
4.1
74
44%
44%
1.1%
176
50
3.6
74
21%
21%
1.9%
301
60
5.2
74
8%
8%
1.7%
269
70
9.2
74
100%
100%
1.3%
331
80
14.3
71
99%
100%
1.9%
568
90
8.9
74
24%
82%
2.0%
286
100
19.3
74
82%
43%
0.6%
573
110
6.1
74
43%
29%
1.3%
531
120A
13.95
74
92%
85%
1.6%
409
120B
2.43
74
92%
50
3.3
165
130
4.5
74
92%
47%
3.7%
207
142
9.9
74
44%
32%
5.0%
608
144-A
0.84
74
2%
100%
0.5%
266
144-B
0.86
74
2%
100%
0.5%
302
144-C
0.75
74
2%
100%
0.5%
239
144-D
0.88
74
2%
100%
0.5%
252
144-E
0.51
74
2%
100%
0.5%
126
144-F
0.47
74
2%
100%
0.5%
201
144-G
0.54
74
2%
100%
0.5%
220
144-H
1.74
74
2%
42%
0.5%
320
146-A
0.81
74
2%
100%
0.5%
86
146-B
1.71
74
2%
100%
0.5%
184
146-C
1.53
74
2%
100%
0.5%
164
146-D
1.99
74
2%
100%
0.5%
193
146-E
0.67
74
2%
28%
0.5%
274
148
1.08
74
2%
10%
16.2%
171
2.2.5 NRCS Curve Numbers
The NRCS curve number approach was used in computing the runoff response in
SWMM. Runoff curve numbers (RCNs) were generated for the pervious areas of the
sub -basins using the NRCS document entitled Urban Hydrology for Small Watersheds,
dated June 1986 and commonly referred to as TR -55. This method relates the drainage
characteristics of soil group, land use category, and antecedent moisture conditions to
assign a runoff curve number. The runoff curve number and an estimate of the initial
surface moisture storage capacity are used to calculate a total runoff depth for a storm in
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Section 2: Hydrology and Hydraulics
a basin.
2.2.6 Channel/Storage Routing
Flood peaks attenuate, or reduce, as they travel downstream due to the storage
characteristic of the channel itself. Channel routing was simulated in the hydraulic
block of SWMM. Routing was modeled using dynamic wave routing. Dynamic wave
routing uses the actual shape and condition of the stream channel input into the
hydraulic model to calculate the attenuated downstream flows.
2.2.7 Summary of Hydrologic Model Results
The EPA SWMM model was used to compute peak runoff for the 2-, 10-, 25-, 50- and
100- year design storms for the existing and proposed conditions. The results of the
existing conditions hydrologic model are summarized in Table 5. A CD containing the
digital files for the SWMM model is included in Appendix E.
Table 5: Comparison of Peak Flows at Radar Road
Condition WQ Event 2 -year
(cfs) (cfs)
Existing 12 63
Proposed 40 288
Storm Event
10 -year
25 -year
100 -year
(cfs)
(cfs)
(cfs)
108
138
185
420
466
513
Although Session Law 2012-200 precludes the project from having to provide detention,
a detailed hydrologic and hydraulic evaluation was performed to confirm there are no
adverse impacts to downstream properties with regards to flooding. A summary of this
evaluation is found in the following Hydraulics section of the report.
2.3 Hydraulics
EPA SWMM 5.0 was chosen as the hydrologic/hydraulic model because of its ability to
model complex drainage systems and to evaluate downstream flooding. The project
involves the construction of a single central high flow rate bioretention pond to provide
water quality treatment for the proposed site development. The airport desires to
reduce the potential for bird strikes by eliminating two existing wet ponds referred to in
this report as the fire suppression wet pond and the existing HAECO site wet pond.
The existing conditions SWMM model attenuates peak flows through these two ponds
to more accurately determine the proposed projects effects on peak flows. To fully
evaluate the project's impacts on downstream properties, the SWMM model was
extended through the Harris Teeter distribution site and immediate downstream open
channel. In addition, a HEC -RAS model was developed to provide a quality control
measure for the changes to water surface elevations developed using EPA SWMM.
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Section 2: Hydrology and Hydraulics
2.3.1 Energy Loss Coefficients
Contraction and expansion of flow produces energy losses caused by transitioning. The
magnitude of these losses is related to the velocity and the estimated loss coefficient.
Where the transitions are gradual, the losses are small. At abrupt changes in cross-
sectional area, the losses are higher. Energy losses resulting from expansion are greater
than losses associated with contraction. Energy loss coefficients used for the SWMM
models are presented in Table 6:
Table 6: Energy Loss Coefficients
Type of Transition Expansion Contraction
None 0 0
Manhole/Inlet 0.35 0.25
Culvert 1.0 0.9 - Projecting from fill CMP
Open Channel 0.3 0.1
Additional energy losses for structures having bends were divided between the two
joining pipes. The bend losses used for this project are based on NCDOT values, and are
shown below in Table 7.
Table 7: Bend Loss Coefficients
Angle (°)
Loss Coefficient
Angle (°)
Loss Coefficient
90
0.70
40
0.38
80
0.66
30
0.28
70
0.61
25
0.22
60
0.55
20
0.16
50
0.47
15
0.10
2.3.2 Starting Water Surface Elevation
The downstream limit of the HAECO Facility Improvements study area is located near
the mouth of Horsepen Creek. The starting water surface elevations for the SWMM
models were generated using the normal depth method based of the channel slope at the
outfall (0.008 ft/ft).
2.3.3 Model Run Descriptions
The EPA SWMM model was used to compute flood elevations at each structure located
in the HAECO Facility Improvements project study area for the water quality event, 2-,
10-, 25-, 50- and 100 -year storm events. A digital copy of the SWMM model is included
on the CD provided in Appendix E.
2.3.4 Hydraulic Evaluation of Radar Road
The following table summarizes the performance of the twin 8.9' x 6.6' corrugated metal
pipe (CMP) arches at Radar Road:
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Section 2: Hydrology and Hydraulics
Table 8: Culvert Performance for at Radar Road
Flood Culvert Invert
Elevation levation
(feet NAVD 1988)
Roadway
Elevation
(feet NAVD 1988)
Existing Water
Surface
Elevations
(feet NAVD 1988)
Proposed Water
Surface
Elevations
(feet NAVD 1988)
WQ Event 831.29 840.90 831.76 832.14
2 -Year
831.29
840.90
832.38
834.07
10 -Year
831.29
840.90
832.72
835.59
25 -Year
831.29
840.90
832.89
836.23
100 -Year
831.29
840.90
833.19
837.18
Although there are increases to peak flows, the downstream drainage system can
accommodate these increased flows. The existing twin 9.8' by 6.6' arched CMPs pass
896 cfs when flowing full. The 104" diameter closed CMP located at the Harris Teeter
distribution center conveys 753 cfs when flowing full. The Radar Road culverts and
Harris Teeter closed pipe will be flowing approximately half full during a 100 -year
storm event therefore there are no impacts to the performance of either of these
drainage systems.
2.3.5 Evaluation of Downstream Flooding
Approximately 85 feet from the top of bank (in the left overbank) is the toe of the water
quality pond embankment for the Harris Teeter distribution center. For this reason, a
check was made to confirm that the additional flows from the HAECO Facility
Improvements project would not cause adverse impacts to the existing water quality
pond embankment. Table 9 summarizes the size, slope and hydraulic characteristics of
the channel located immediately downstream of Harris Teeter.
Table 9: Hydraulic Summary of Harris Teeter Open Channel
Bottom Top
Side
Channel Channel
Floodplain
Depth
Width Width
Slopes
Slope Capacity
Capacity
(feet)
(feet) (feet)
(ft/ft)
(ft/ft) (cfs)
(cfs)
10 25 4
2:1
0.014 300
2,150
Assumed Manning's 'n' value= 0.06
Floodplain capacity is the flow needed to inundate
the toe of the existing Harris Teeter pond
As shown in Table 9, the existing channel can almost convey the proposed conditions
10 -year flood without overtopping its banks. The flow needed to inundate the lowest
toe elevation of the Harris Teeter pond is 2,150 cfs which is significantly more than the
513 cfs that will leave the proposed HAECO site.
This existing open channel extends approximately 290 feet downstream of the Harris
Teeter culvert prior to entering Horsepen Creek which is a FEMA stream with an 832 -
acre (1.3 square miles) drainage area and 100 -year peak flow of 1,598 cfs. On the
upstream side of Radar Road (along Horsepen Creek), the drainage area increases to
HAECO Facility Improvements Project Page 2-6
Stormwater Report

Section 2: Hydrology and Hydraulics
1,344 acres (2.1 square miles) with a 100 -year peak flow of 3,018 cfs. A field walk and
inspection of aerial topography shows this reach of Horsepen Creek does not have any
insurable structures located in the reach upstream of Radar Road where the 329 cfs
increase would be roughly 10% of the total flow in Horsepen Creek. As shown in this
report, the proposed HAECO Facility Improvements Project will not adversely cause
flooding downstream to an insurable structure or road.
Figure 1: FEMA FIRM Panel
2.3.6 Closed Drainage Systems
Closed systems were designed to pass the 10 -year flood without surcharging the pipe.
With the exception of the SCM underdrain system, all drainage pipes are reinforced
concrete (RCP).
2.3.7 Outfall Protection for Closed Drainage System
Rip -rap pads are proposed at two locations in the high flow rate bioretention. These
outfalls are located where the flows enter back into the natural drainage system or the
bioretention ponds. The NY DOT method was used to design the length, width, depth
and size of the rip -rap pads. Appendix F shows the calculation used to size the rip -rap
pads.
HAECO Facility Improvements Project Page 2-7
Stormwater Report

Section 3: Water Quality Compliance
3.1 Overview
To satisfy the water quality requirements outlined in Session Law 2012-200, a proposed
0.8 -acre high flow rate bioretention pond is being proposed. Session Law 2012-200
requires runoff generated from the 1st inch of rainfall for a development project shall be
infiltrated into the ground. There are no specific requirements to remove total
suspended solids (TSS), nitrogen, or phosphorus. In addition, there are no requirements
to detain the 1 -year or any other storm event to at or below pre -project conditions. As
shown in this report, the proposed high flow rate bioretention pond exceeds the
minimum infiltration requirements set forth in Session Law 2012-200.
3.1.1 Proposed Impervious Areas
The separately attached construction plans and concept plan provided in Appendix A
show the proposed pond, new and existing impervious areas, location of flow splitters
and overall site layout. The following table summarizes the proposed impervious areas
associated with the HAECO Facility Improvements project:
Table 10: Minimum Area of Impervious Cover Required for Treatment
Location Impervious Cover (acres)
Proposed Hangar 5.06
Proposed Apron 5.11
Proposed Fire Access Roads 0.32
Proposed Sidewalk 0.09
Existing HAECO Site to the East 14.03
TOTAL = 24.61 acres
Because the existing fire suppression pond is being abandoned as part of this project, the
proposed SCM will need to be designed to accept runoff from the system currently
going to the existing fire suppression pond. The stormwater runoff generated in sub -
basins 60, 70 and 80 will be redirected into the proposed SCM. Appendix C highlights
the areas that will drain to the pond along with a breakdown for the impervious area
contributed from each sub -basin. As a result, an additional 20.49 acres of impervious
area will be infiltrated in the proposed SCM as shown in the following table:
Table 11: Proposed Impervious Cover to SCM
Location
Impervious Cover (acres)
Proposed Hangar
3.35
Proposed Apron
5.11
Proposed Fire Access Roads
0.32
Proposed Side Walk
0.09
Existing HAECO Site to the East
11.92
Sub -Basin 60
0.42
Sub -Basin 70
9.22
Sub -Basin 80
14.09
TOTAL = 44.52 acres
HAECO Facility Improvements Project Page 3-1
Stormwater Report

Section 3: Water Quality Compliance
In total, the proposed SCM will have a contributing drainage area of 54.0 acres with
44.52 acres of impervious cover.
3.1.2 High Flow Rate Bioretention Pond Design Criteria
The State BMP Manual does not specifically have a set of design guidelines for a high
flow bioretention pond so the following guidelines were used in the design of the
proposed high flow bioretention pond:
♦ Infiltrate 100% of the runoff generated from the 1St inch of rainfall;
♦ Side slopes shall be no steeper than 3(H):1(V);
♦ SCM shall be located in a recorded drainage easement;
♦ A bypass or internal overflow is required for bypassing storm flows in excess of
the design flow;
♦ Media permeability shall be between 6 and 10 inches per hour with a targeted
detention time of 10 to 15 hours for infiltrating the water quality volume;
♦ Ponding depth for the water quality event shall be limited to 4.0 feet;
♦ Media depth will be 2 feet for each of the two soil media zones of the
bioretention pond;
♦ An underdrain shall be located under the soil media to keep the pond dry and
prevent groundwater from entering the pond; and
♦ A rip -rap energy dissipater shall be located at the outfall of each pipe entering
the pond.
3.1.3 Water Quality Volume (WQV)
The volume of runoff generated from the 1St inch of rainfall was calculated using an in-
house spreadsheet based on the Schuler Simple Method. This spreadsheet shows the
calculated water quality volume along with proposed SCMs stage -storage sizing (see
Appendix G). The following table summarizes the minimum required volume along
with the provided volume:
Table 12: Calculated Storage Volumes
Description Impervious Area Surface Runoff
(acres) (ft3)
Required Area for Treatment 25.01 72,582
Compensatory Treatment of Sub -basins 60, 70, 80 23.72 82,679
Total Provided Area for Treatment 44.52 155,260
Net Credit for WQ Treatment 19.51 82,678
As shown in Table 12, the proposed high flow rate bioretention pond will infiltrate an
additional 82,678 cubic feet of runoff and 19.51 acres of impervious cover more than
required.
HAECO Facility Improvements Project Page 3-2
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Section 3: Water Quality Compliance
3.1.4 Pond Design Summary
A concrete riser structure is proposed to control flows leaving the high flow rate
bioretention pond. The primary spillway will include the following elements: a poured,
reinforced concrete box riser and reinforced concrete outfall pipe with gaskets at joints.
Because the weir length on these structures is 12' and the flows entering the ponds are
generally very small, there were no emergency spillways proposed for the pond. The
following is a summary of the design for the proposed high flow rate bioretention pond
(See the separately attached plan set for additional details):
♦ Surface Area: The proposed high flow rate bioretention pond is larger than the
minimum size needed to achieve the water quality goals of the project. The
surface area of the pond was achieved by targeting a pond depth of less than 4.0
feet and a detention time between 10 and 40 hours. The more well -draining the
soils the smaller the footprint of the pond needed to drain the pond in
approximately 10 hours. As shown in this report, the surface area that drains the
pond in approximately 11 hours is 28,005 square feet (0.64 acres).
♦ Primary Outfall: A concrete box riser with an outside dimension of 7'x7' is
proposed with a primary weir elevation set at 583.75 feet NAVD 1988. The total
weir length of the primary outfall is 18 feet (four 4.5' long weirs).
♦ Emergency Overflow: The primary spillway was designed to pass flow larger
than the 100 -year flood without overtopping the top of dam. A 15' wide rip -rap
lined emergency overflow will convey flows over the top of dam should the riser
be clogged for some unforeseen reason. This emergency spillway ties into a
grass lined swale until it reaches an 18" RCP with a flared section opening.
♦ Top of Dam: The top of dam is set at elevation 855.25 feet which is approximately
1.7 feet above the 100 -year flood elevation. The total dam height measured from
the toe of the embankment on the downstream side is approximately 3.0 feet.
The following table summarizes the water surface elevations at the proposed pond for
the water quality event, 1-, 10- and 100 -year floods:
Table 13: Water Surface Elevations at Proposed Pond
Water Quality 1 -Year Storm
Event (NAVD'88)
853.28 853.48
10 -Year Storm 100 -Year Storm
(NAVD'88) (NAVD'88)
853.50 853.52
Riser
The riser detail provided in the separately attached plan set shows the 6'x6' concrete box
to control water surface elevations inside the proposed SCM. The primary spillway was
set at elevation 853.30 feet which is the dynamic elevation calculated inside EPA SWMM
for the water quality storm event (an NRCS Type I1 distribution with 1.0 inches of
HAECO Facility Improvements Project Page 3-3
Stormwater Report

Section 3: Water Quality Compliance
rainfall). The riser has a 42" diameter RCP barrel that conveys flow from the pond to a
new 48" diameter closed drainage system. This 48"diameter closed system conveys the
by-pass flows for larger storm events from the eastern side of the existing HAECO
development. An anti -floatation calculation (See Appendix H) was performed for the
pond riser resulting in a factor of safety of 1.22. This calculation ignores the friction
forces of the underlying soil and therefore a factor of safety larger than 1.22 would be
achieved in real conditions. Because this is a dry pond and water levels will rarely reach
6" above the crest of the weir therefore a factor of safety of 1.22 is acceptable.
Flow Splitters
Three flow splitters are proposed to divert stormwater runoff from the proposed closed
drainage system into the high flow rate bioretention pond. For water quality rainfall
event (1.0 inch of rain), 100% of the runoff generated will flow directly into the high flow
rate bioretention pond. Inside each flow splitter is a weir wall that will direct flows
generated from larger storm events into a closed by-pass pipe. The elevation of this weir
wall was calculated in EPA SWMM by iteratively adjusting the elevation of the wall
until no flow was being diverted in the water quality rainfall event.
The splitter box located just north and west of the pond (Structure 5) will require a
special design. Flows that go over the weir wall will drop into a concrete manhole
structure and eventually into the sites main 72 inch diameter RCP. The following table
summarizes the key elevations for the three proposed concrete flow splitters:
Table 14: Summary of Flow Splitter Design
Pipe to Pond
Pipe to Pond
Diameter (in)
Splitter #
Invert Elevation
Weir Wall Height
15"
(feet NAVD 1988)
(ft)
1 (structure 20)
872.21
0.85
2 (structure 25)
855.10
2.75
3 (structure 5)
851.68
1.45
Pipe Sizes
Pipe to Pond
Entering Splitter
Diameter (in)
Box (in)
10 -Year Storm Event
30"
15"
48"
24"
54" and 42"
30"
The separately attached design plans provide additional details on the size and
construction of the flow splitters being used for this project.
Table 15: Flow Splitter Performance
Splitter #
Water Quality Event
10 -Year Storm Event
Flow To Pond Flow Around Pond
Flow To Pond
Flow Around Pond
(cfs) (cfs)
(cfs)
(cfs)
1 (structure 20)
4 0
6
17
2 (structure 25)
10 0
20
50
3 (structure 5)
27 0
40
121
As shown in Table 15, approximately 67% of the peak flows from the larger storm events
will be diverted around the pond.
HAECO Facility Improvements Project Page 3-4
Stormwater Report

Section 3: Water Quality Compliance
Detention Time and Soil Media for High Flow Rate Bioretention Pond
Per discussions with DEQ, it was agreed that the proposed high flow rate bioretention
pond would detain the water quality event for between 10 and 40 hours. To achieve this
goal, a well -draining sand media is needed that promotes infiltration at a rate that is not
too quick (3 or 4 hours) and not too long (over 40 hours). With an assumed infiltration
rate of 10 inches per hour for this well -draining sand, a footprint was iteratively
determined until the time to drain the pond was 10 hours. This area was calculated to
be 14,563 square feet. For those areas outside the well -draining sands an infiltration
rate of 2 inches/hour was assumed. As shown in Appendix I, the combined flow rate
passing through the soil media and leaving the pond is 3.9 cfs.
For the area of well -draining sand, the construction of the high flow rate bioretention
pond will mimic the design of a PGA golf green. It is assumed that the best draining
soils that can be stockpiled from the onsite borrow area will be used for those areas
outside the well -draining sands. At a minimum this media in Zone 1 will have a
permeability of 2 inches/hour. The following is a summary of the construction for the
area of the pond that mimics the PGA golf green:
Option #1 for Zone 2 (No. 57 Stone at base)
• 12" thick base of No. 57 stone (approximately 3/4' in size)
• 4" of washed sand
• 2' of well -draining sand -soil mix (with a permeability of 10 inches/hour)
Option #2 for Zone 2 (Pea Gravel at base)
• 12" thick base of peak gravel (100% passage of 3/8" sieve)
• 2' of well -draining sand -soil mix (with a permeability of 10 inches/hour)
Specifications for the two soil zones will be prepared at final design.
Channel Liner
As shown on the separately attached design plans, two shallow rip -rap lined swales are
proposed to convey runoff from small storm events to the side of the SCM with the riser.
The swales were designed to be relatively shallow (1 foot in depth) and flat in order to
promote infiltration. It was assumed that the entire pond bottom would be inundated
fairly quickly and the need to size a large swale to minimize erosion would not be
necessary. A calculation for the channel liner design is provided in Appendix J.
Maintenance and Operation Procedures
A maintenance and operation plan for the bioretention facilities has been included with
this report as Appendix K.
HAECO Facility Improvements Project Page 3-5
Stormwater Report

Section 3: Water Quality Compliance
3.2 Conclusion
As shown in this report, the proposed high flow rate bioretention pond is designed to
bring the HAECO Facility Improvements project at the Piedmont -Triad International
Airport in compliance with the State's requirements for water quality as outlined in
Session Law 2012-200. By diverting runoff for the water quality rainfall event from
basins 60, 70 and 80 into the proposed SCM, the airport is providing treatment for 44.52
acres of impervious cover. As shown in this report, the proposed SCM is providing
approximately 19.51 acres more than the minimum required amount. The airport would
like to request a water quality credit to offset the need to provide or minimize treatment
with a future onsite development.
HAECO Facility Improvements Project Page 3-6
Stormwater Report

WDICKSON
communily Inlfaslructure consultants
Proposed Concept Plan - Appendix A
High Flow Rate Bioretention Pond
Piedmont -Triad International Airport
HAECO Site Development
200 100
1 inch = 200 feet
200 Feet

Project: HAECO Facility Improvement @ PTIA, Greensboro, NC
Prepared by: DJK
Date: November 9, 2015
SWMM Input Data
Appendix B
EXISTING CONDITIONS
SUBBASINS
Flow
Basin
Percent
SWMM Sub-
Pervious
Area
Width
Elevation
(sq. ft.)
Length
Slope
Impervious
Basin ID
RCN(acres)Area
(ft.)
Change (ft.)
(ft )
M
M
10
74
77.1
3356329
3294
1019
21
0.64%
31%
20
74
28.8
1253061
1259
995
11
0.83%
34%
30
74
19.3
842697
1856
454
19
1.03%
40%
40
74
4.1
180429
1027
176
12
1.12%
44%
50
74
3.6
156421
520
301
10
1.92%
21%
60
74
5.2
225908
841
269
14
1.66%
8%
70
74
9.2
401743
1215
331
16
1.34%
100%
80
71
14.4
627272
1095
573
21
1.91%
100%
85
71
3.0
131013
338
388
36
10.65%
24%
90
74
8.9
388935
1359
286
27
1.98%
82%
100
74
19.3
840092
1465
573
9
0.58%
43%
110
74
6.1
263574
496
531
7
1.31%
29%
120
74
15.3
665778
958
695
25
2.56%
92%
130
74
4.5
195877
944
207
35
3.65%
44%
142
74
9.4
407511
707
576
35
4.95%
26%
145
74
12.2
529689
1513
350
49
3.25%
2%
240.27
PROPOSED CONDITIONS SUBBASINS
Flow
Basin
Percent
SWMM Sub-
Pervious
Area
Width
Elevation
Area (sq. ft.)
Length
Slope
Impervious
Basin ID
RCN
(acres)
(ft.)
Change (ft.)
(ft.)
(%)
(%)
10
74
77.05
3356329
3294
1019
21
0.6%
31%
20
74
28.77
1253061
1259
995
11
0.8%
34%
30
74
19.35
842697
1856
454
19
1.0%
40%
40
74
4.14
180429
1027
176
12
1.1%
44%
50
74
3.59
156421
520
301
10
1.9%
21%
60
74
5.19
225908
841
269
14
1.7%
8%
70
74
9.22
401743
1215
331
16
1.3%
100%
80
71
14.09
613567
1095
560
21
1.9%
100%
90
74
8.93
388935
1359
286
27
2.0%
82%
100
74
19.29
840092
1465
573
9
0.6%
43%
110
74
6.05
263574
496
531
7
1.3%
29%
120A
74
13.95
607823
1487
409
25
1.6%
85%
1208
74
2.43
105911
640
165
21
3.3%
50%
130
74
4.50
195877
944
207
35
3.7%
47%
142
74
9.36
407511
707
576
35
5.0%
32%
144-A
74
0.84
38104
143
266
0.715
0.5%
100%
144-B
74
0.86
38293
127
302
0.635
0.5%
100%
144-C
74
0.75
32703
137
239
0.685
0.5%
100%
144-D
74
0.88
38306
152
252
0.76
0.5%
100%
144-E
74
0.51
22097
175
126
0.875
0.5%
100%
144-F
74
0.47
20479
102
201
0.51
0.5%
100%
144-G
74
0.54
23709
108
220
0.54
0.5%
100%
144-H
74
1.74
75931
237
320
1.185
0.5%
42%
146-A
74
0.81
35111
406
86
2.03
0.5%
100%
146-B
74
1.71
74691
406
184
2.03
0.5%
100%
146-C
74
1.53
66657
406
164
2.03
0.5%
100%
146-D
74
1.99
86824
450
193
2.25
0.5%
100%
146-E
74
0.67
29025
106
274
0.53
0.5%
28%
148
74
1.08
47109
275
171
44
16.2%
10%
240.27

�wl<
iDICKSON
community infrastructure consultants
Existing Conditions Drainage Area Map - Appendix C
Piedmont -Triad International Airport
HAECO Site Development
500 250 0 500 Feet
1 inch = 500 feet

I
1
1
�wl<
iDICKSON
community infrastructure consultants
Contributing Drainage Areas and Impervious Cover to SCM - Appendix C 4-1
Piedmont -Triad International Airport r.
HAECO Site Development
300 150 0
300 Feet
1 inch = 300 feet

I
�wl<
W DICKSON
community infrastructure consultants
Existing Landuse Map - Appendix D 4 500 250 0 500 Feet
Piedmont -Triad International Airport s
HAECO Site Development 1 inch = 500 feet

�wl< Proposed Landuse Map - Appendix D 4-500 250 0 500 Feet
W DICKSON Piedmont -Triad International Airport s�
community infrastructure consultants HAECO Site Development 1 inch = 500 feet

25
z 20
LENGTH MINIMUM
U
OF THICKNESS
STONE STONE
��
15
�
r\
2 STONE LIGHT 6"
6 X O 12"
�
` 1
10
O
8 X D 30'
5 STONE HEA VY 23"
10 X D 30"
6 STONE HEAVY 23"
5
m
5
10 �15
DIAMETER OF PIPE IN FEET
APPENDIX F
ZONE APRON CLASS SIZE
LENGTH MINIMUM
MATERIAL OF OF
OF THICKNESS
STONE STONE
APRON k OF STONE
I STONE FINE J.
4 X 0 9"
2 STONE LIGHT 6"
6 X O 12"
3 STONE MEDIUM l3"
8 X D 18"
4 STONE HEAVY 23"
8 X D 30'
5 STONE HEA VY 23"
10 X D 30"
6 STONE HEAVY 23"
12 X D 30"
REQUIRES LARGER STONE OR ANOTHER TYPE OF
7 DEVICE. DESIGN IS BEYOND THE SCOPE OF THIS
PROCEDURE.
WWDTH V
WDTH = DIAMETER f D.4 (LENGTH)
: 6� MINIMUM
LENGTH TO PREVENT SCOUR HOLE, MIN LENGTH 1D'
i
i
i NAME I 910CHT SIZE SPECIFICATIONS
i
' RIP -RAP
iI 30% SHALL WEIGH AT LEAST 100
CLASS 1 5 — 200 LBS EACH. NO MORE THAN 102'
SHALL NEIGH LESS THAN 15 LBS
EACH.
60% SHALL WEIGH AT LEAST 100
20 25 CLASS 2 25 — 250
LBS
&L EACH.
SS THANA 50 LBS.
EACH.
EROSION CONTROL STONE
CLASS A 2" _ B" 108 TOP & 8OTTOM SIZES
NO GRADATION SPECIFIED.
CLASS B 15 — 300 NO GRADATION SPEC0ED.
STRUCTURE
LOCA17ON
Q—FLDW
DIAMETER OF
OUTLET
DEPTH
N1DOT
APRON
APRON
APRON
APRON
RIP—RAP REMARKS
OR
(CFS)
PIPE
VELOCITY
OF FLOW
ZONE
LENGTH
WIDTH 3Do
WWDTH V
THICKNESS
CLASS
LINE
(IN.)
(FTS.)
(FT.)
(FT)
(FL)
(FT)
(IN.)
PADA
PIORETENTION POND
3D
36
4.J
1.3
2
18
9
10
24"
TYPE I RIP—RAP
PAD,f2
l
EVORETENTION POND
26
24
5.4
1.4
2
-
15
6
8
24"
TYPE I RIP—RAP
4
SOURCE; BANK & CHANNEL LINING PROCEDURES,
NEW YORK DEPARTMENT OF TRANSPDRTAlION,
DIVISION OF DESIGN AND CONSTRUCRON, 1971.
7za 04, Me r�N1ER DRIVE
W,K1 720 0N, NC Z7Ba7
DICKSON (918) 7B2—a19B
orcr<. �uans
North t. o ha
communityGaargia
infrastructure consu€tants samh Cwdma no tla

Appendix G
Water Quality Volume and Stage Storage at Proposed Central High Flow Bioretention Pond
Project: HAECO Facility Improvement @ PTIA, Greensboro, NC
Prepared by: DJK
Checked by:
Date: November 3, 2015
Summary of Inovervious Areas
Stage -Storage from Contours - Proposed Detention Facility - High Flow Bioretention Pond
Impervious Area
Total Drainage
Description
ac)
Area ac)
Basin 60
.42
5.1
Basin 70
9.22
9.22
Basin 80
14.09
14.09
Basin 120
11.92
13.95
ProposedApron
5.11
6.59
Proposed Hangar
5.06
5.95
Proposed Access Rd
0.32
0.66
Hangar Area Not Draining to Pond
-1.71
-1.71
Proposed Sidewalk
0.09
0.09
Tota(
44.52
54.03
EI,yiA - . Planners . S. -y -
L -d -Pt Atthile 15
R„ Runoff coefficient
The R. is a measure of the site response to rainfall events, and in theory is calculated as:
R,. = r y, where r and p are the volume of storm runoff and storm rainfall,
respectively, expressed as inches.
The R, for the site depends on the nature of the soils, topography, and cover. However, the
primary influence on the R,, in urban areas is the amount of imperviousness of the site.
Impervious area is defined as those sufaces in the landscape that cannot infiltrate rainfall
consisting of building rooftops, pavement, sidewalks, driveways, etc. In the equation R„ _
0.05 + 0.009(1), "P' represents the percentage of impervious cover expressed as a whole
number. A site that is 75% impervious would use I = 75 for the puposes of calculating R..
Calculate the runoff coefficient:
Rv=0.05+0.009(la) Calculate the required volume to be detained for the first 1" of runoff:
Rv = runoff coefficient = storm runoff (inches) / storm rainfall (inches) Volume = (Design rainfall)(Rv)(Drainage Area)
la = percent impervious = impervious portion of the drainage area (ac.)/drainage area (ac.) Volume = 1" rainfall * Rv * 1/12 (feet/inches) * Drainage Area
la 82.40 Volume = 3.6 acre-feet
Rv= 0.79 (in./in.) Volume = 155,260 W
Stage Storage Relationship V.2 = %(A, +AZ+ A, • AZ
Incremental volume determined using "conic" method as described in USACE HEC -1 manual
Pond bottom
Elevation that exceeds the water quality volume (assuming static elevation with no infiltration)
Stage -Storage from Contours - Proposed Detention Facility - High Flow Bioretention Pond
S
S
SW MM
CONTOUR
INCREMENTAL
ACCUMULATIVE
TOTAL
NODE INVERT
CONTOUR
DEPTH
AREA
VOLUME
VOLUME
VOLUME
(FT)
(FT)
(FT)
(AC)
(SF)
(GAL)
(CF)
(AC -FT)
(GAL)
(CF)
(AC*FT)
(%)
848.50
848.50
0.00
0.00
1
849.00
0.50
0.00
2
6
1
0.000
6
1
0.000
0%
850.00
1.50
0.00
319
2
0.000
24
3
0.000
0%
Pond Bottom
851.00
2.50
0.33
14,563
36842
4925
0.113
36,866
4,928
0.113
2% 1
852.00
3.50
0.56
24,328
143909
19238
0.442
180,775
24,166
0.555
8%
853.00
4.50
0.60
26,138
188715
25228
0.579
369,490
49,394
1.134
17%
854.00
5.50
0.64
28,005
202469
27066
0.621
571,959
76,460
1.755
26%
855.00
6.50
0.69
29,929
216648
28962
0.665788,607
105,421
2.420
36%
856.00
7.50
0.73
31,910
231254
30914
0.710
1,019,862
136,336
3.130
47%
856.60
8.35
0.76
33,133
145958
19512
0.4481,
165,819
155,847
3.578
54%
857.00
8.50
0.78
33,948
246287
32924
0.756
1,266,148
169,259
3.886
58%
858.00
9.50
0.83
36,043
362123
48409
1.111
1,628,271
217,668
4.997
75%
859.00
10.50
0.88
38,196
539362
72102
1.655
2,167,634
289,770
6.652
100%
Incremental volume determined using "conic" method as described in USACE HEC -1 manual
Pond bottom
Elevation that exceeds the water quality volume (assuming static elevation with no infiltration)

Riser Structure Flotation Calculation
Project: HAECO Site Development
Prepared by: DJK
Dated: 11-3-15
Appendix H
_alc
QC Check on Calcs
Inside Lgth (ft) (perpendicular to flow)
Inside Width (ft)
Outside Loth (ft) (perpendicular to flow)1
Bottom of pond with regards to soil (invert of underdrain system is 848.5
Invert Out Elev.
1 6.00
5.30
5.30
0.67
I 0.50
1.25
848.00
Primary Weir Elev.
853.30
0.00
0.00
42.00
9.62
Overflow Weir Elev.
853.30
Concrete weight (lbs/cu ft)
Water weight (lbs/cu ft)
(Secondary Weir Hght (ft)
1.50
99.20 Weir capacity
Secondary Weir Width (ft)
4.67
calc
Primary Weir Hght (ft)
1.50
calc
Primary Weir Width (ft)
4.67
calc
Top of Box Elev.
855.30
calc
Appendix H
_alc
QC Check on Calcs
Inside Lgth (ft) (perpendicular to flow)
Inside Width (ft)
Outside Loth (ft) (perpendicular to flow)1
4.67
I 4.67
6.00
Outside Width (ft)
Primary weir hgth (ft) (CALCULATED) 1
Overflow weir hgth (ft) (CALCULATED)
Wall thickness (ft)
Top thickness (ft)
Base thickness (ft)
1 6.00
5.30
5.30
0.67
I 0.50
1.25
Inside width of box
5.67
Orifice diameter (in)
,Orifice area (sq -ft)
Outlet pipe dia (in)
Outlet pipe area (sq ft)
0.00
0.00
42.00
9.62
7.00
Concrete weight (lbs/cu ft)
Water weight (lbs/cu ft)
146.00
62.40
Probable
�Str volume (cu -yd)
4.89
Height of box (below top)
4.8
Str weight (lbs)
19,267
81.066667 cu ft
Buoyant force (lbs)
15,837
_alc
Thickness of top
Resultant weight (lbs)
3,430
Volume of top
24.5 cu ft
Factor of Safety
1.22
61.25 cu ft
Bearing Weight (lbs/sq ft)
535.19
Weight of Concrete
Appendix H
_alc
QC Check on Calcs
_alc
Check on Volume
_alc
Inside width of box
5.67
_alc
Outside width of box
7.00
Area of inside box
32
Area of outside box
49
Design Input (Target factor of safety of 1.2)
Height of box (below top)
4.8
Net Volume of Walls
81.066667 cu ft
Top Area of structure
49
_alc
Thickness of top
0.50
Volume of top
24.5 cu ft
:alc
Volume of base
61.25 cu ft
Total Volume of Concrete
166.81667
Weight of Concrete
24,355
Conservative Assumptions:
Bouyant force measured at top of structure lid
100 -year flood depth is 8.6 feet in depth (calculation went to elevation 9.5 feet)
Weight of soil on outfall pipe not accounted for in calculation
Anti-Floatation.xls
Volume of displaced water 320.95 cu ft
Unit weight of water 62.4
Force of displaced water 20,027
Factor of Safety 1.22

Detention Time and Design of High Flow Rate Media
Project: HAECO Facility Improvement @ PTIA, Greensboro, NC
Prepared by: DJK
Checked by:
Date: October 23, 2015
Description
Basin 60
Basin 70
Basin 80
Basin 120
Proposed Apron
Proposed Hangar
Proposed Access Rd
Total
Impervious Area (ac)
0.4
9.2
14.1
11.9
5.1
5.1
0.3
44.5
Total Drainage Area (ac)
5.2
9.2
14.1
14.0
6.6
6.0
0.7
54.0
Calculate the runoff coefficient:
Rv=0.05+0.009(la)
Rv = runoff coefficient = storm runoff (inches) / storm rainfall (inches)
la = percent impervious = impervious portion of the drainage area (ac.)/drainage area (ac.)
Ia 82.40
Rv= 0.79 (in./in.)
Calculate the runoff volume for the water quality event (first 1" of runoff):
Volume = (Design rainfall)(Rv)(Drainage Area)
Volume = 1" rainfall * Rv * 1/12 (feet/inches) * Drainage Area
Volume = 3.6 acre-feet
Volume = 155,260 ft3
DWK
[31 CHCS(3N
I.an4yap, AmFOWts
Appendix I
Infiltration Zone and Assumed Infiltration Rates for Pond
Assumed Infiltration Rate Assumed Infiltration Rate Assumed Infiltration
Zone Area (sq ft) (inch/hr) Whr) Rate (ft/sec)
1 (moderately draining soils) 12,403 2 0.2 0.000046
2 (well draining sand) 14,563 10 0.8 0.000231
Calculate Peak Flows and Drawdown Time for WQ Event
Time to Drain Pond Time to Drain
Zone 1 Peak Flow (cfs) Zone 2 Peak Flow (cfs) Total Flow (cfs) Time to Drain Pond (sec) (min) Pond (hours)
0.6 3.4 3.9 39,354 656 10.9

Shear Stress Analysis of Rip -Rap Ditches Inside SCM Pond
Project: HAECO Site Development Project, PTIA Airporl
Engineer: DJK
Date: 11-3-15
Appendix J
Mannings Equation, Q =(A) 1.49 Rh.66S0.5
n
36 Inch RCP on Western Side of Pond
Storm
Design
Chan Bot
Side Side Slope
Design
Chan
Wetted
Hydraulic
Mann.
Channel
Q
Calc.
Calc.
Shear
Temp.
Perm.
Event
Flow (cfs)
Width
Slope Length
Depth
Area
Perim., Pw
Radius
"n"
Slope
Allow.
Depth
Velocity
Stress
Liner
Liner
10 -Year
30
3
3 6.3
2
18
16
1.2
0.040
0.002
32
1.9
1.8
0.2
Straw w/ net
Class A
1 -Year
9
3
5 5.1
1
8
13
0.6
0.040
0.002
9
1.0
1.2
0.1
Straw w/ net
Class A
24 Inch RCP on Eastern Side of Pond
Storm
Design
Chan Bot
Side Side Slope
Design
Chan
Wetted
Hydraulic
Mann.
Channel
Q
Calc.
Calc.
Shear
Temp.
Perm.
Event
Flow (cfs)
Width
Slope Length
Depth
Area
Perim., Pw
Radius
"n"
Slope
Allow.
Depth
Velocity
Stress
Liner
Liner
10 -Year
26
3
3 6.3
2
18
16
1.2
0.040
0.002
33
1.9
1.8
0.2
Straw w/ net
Class A
1 -Year
9
3
5 5.1
1
8
13
0.6
0.040
0.002
9
1.0
1.2
0.1
Straw w/ net
Class A
IShear Stress, T= yds
T = shear stress in Ib/sq. ft.
y = unit weight of water, 62.4 Ib/cu. ft.
d = flow depth in ft.
s = channel slope in ft./ft.
Notes:
Side slope = horiz./vert.
TemporaryLiners
AllowSheafitress
Material
(lb/sglt)
Tacked Mulch
0.35
Jute Net
0.45
Straw w/Net
1.45
SytheticMat
2.00
C1assA
1.25
ClassB
2.00
Classl
3.40
Classll
4.50
Max Permi ss ibb Vel ocitiesfor Unpro eeted Sot l sin Ex. Channels
Material
Max. Permissibb Velocity(ff/s)
FineSand(noncollidl)
2.5
Sand Loam(nonco I I idl)
2.5
Si ltLoam(noncollidl)
3.0
OrdinaryFirm Loam
3.5
Fine Gravel
5.0
Stiff Clay (very collidal)
5.0
Graded,Silt toCobbles
5.0
IDepth and Velocity calculated using AutoCAD's Hydroflow Express
Max. Allow. Design V for Vegetative Channels
ChannelSlope Soil
GrassLining
Permissibb V (11/s)
0-5% Sands/Silk
Bermuda
5.0
Tall Fescue
4.5
KYBluegrass
4.5
Grass-legumemix
3.5
Clay Mixes
Bermuda
6.0
Tall Fescue
5.5
KY Bluegrass
5.5
Grass-leguinemix
4.5
5-10% Sands/Silt
Bermuda
4.5
Tall Fescue
4.0
KYBluegrass
4.0
Grass- legume mix
3.0
Clay Mixes
Bermuda
5.5
TallFescue
5.0
KYBluegrass
5.0
Grass-legumemix
3.5

Permit Number:
(to be provided by DEMLR)
Drainage Area Number:
High Flow Rate Bioretention Pond
Operation and Maintenance Agreement
I will keep a maintenance record on this BMP. This maintenance record will be kept in a
log in a known set location. Any deficient BMP elements noted in the inspection will be
corrected, repaired or replaced immediately. These deficiencies can affect the integrity
of structures, safety of the public, and the removal efficiency of the BMP.
Important maintenance procedures:
— The drainage area of the high flow rate bioretention pond will be carefully
managed to reduce the sediment load to the sand filter.
— Once a year, sand media will be skimmed.
— The sand filter media will be replaced whenever it fails to function properly after
maintenance.
The high flow rate bioretention pond will be inspected once a quarter and within 24
hours after every storm event greater than 1.0 inches. Records of operation and
maintenance will be kept in a known set location and will be available upon request.
Inspection activities shall be performed as follows. Any problems that are found shall
be repaired immediately.
BMP element:
The entire BMP
The grass filter strip or
other pretreatment area
The flow diversion
structure (if applicable)
Potential problem:
Trash/debris is present.
Areas of bare soil and/or
erosive gullies have formed
Sediment has accumulated to
a depth of greater than six
inches.
The structure is clogged
The structure is damaged
How I will remediate the problem:
Remove the trash/debris.
Regrade the soil if necessary to
remove the gully, and then plant a
ground cover and water until it is
established. Provide lime and a
one-time fertilizer application.
Search for the source of the
sediment and remedy the problem if
possible. Remove the sediment and
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Unclog the conveyance and dispose
of any sediment off-site.
Make any necessary repairs or
replace if damage is too large for
repair.
High Flow Rate Bioretention Pond O&M Page 1 of 3

BMP element:
The bioretention cell:
soils and mulch
Permit Number:
Potential problem:
Mulch is breaking down or
has floated away.
Soils and/or mulch are
clogged with sediment. Water
is ponding on the surface for
more than 24 hours after a
storm.
(to be provided by DEMLR)
How I will remediate the problem:
Spot mulch if there are only random
void areas. Replace whole mulch
layer if necessary. Remove the
remaining mulch and replace with
triple shredded hard wood mulch at
a maximum depth of three inches.
Check to see if the collection system
is clogged and flush if necessary. If
water still ponds, remove the top
few inches of the filter bed material
and replace. If water still ponds,
then consult an expert.
Outlet device Clogging has occurred. Clean out the outlet device and
dispose sediment in a location that
will not impact a stream or the
BMP.
The outlet device is damaged. Repair the outlet device.
The observation well(s) The water table is within one Contact DEMLR Stormwater
foot of the bottom of the Permitting staff immediately at
system for a period of three 919-707-9220.
consecutive months.
The emergency overflow
berm
The receiving water
The outflow pipe is clogged
The outflow pipe is damaged.
Erosion or other signs of
damage have occurred at the
outlet.
Erosion or other signs of
damage have occurred at the
outlet.
Provide additional erosion
protection such as reinforced turf
matting or riprap if needed to
prevent future erosion problems.
Repair or replace the pipe.
The emergency overflow berm will
be repaired or replaced if beyond
repair.
Contact the N.C. Division of Water
Resources 401 Certification Program
staff at 919-707-8789.
High Flow Rate Bioretention Pond O&M Page 2 of 3

Permit Number:
(to be provided by DEMLR)
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 DEMLR of
any problems with the system or prior to any changes to the system or responsible party.
Project name: HAECO Site Development Project
BMP drainage area number:
Print name:
Title:
Address:
Phone:
Signature:
Date:
Note: The legally responsible party should not be a homeowners association unless
more than 50% of the lots have been sold and a resident of the subdivision has
been named the president.
a Notary Public for the State of
County of , do hereby certify that
personally appeared before me this _
day of , and acknowledge the due execution of the
forgoing high flow rate bioretention pond maintenance requirements. Witness my hand
and official seal,
SEAL
My commission expires
High Flow Rate Bioretention Pond O&M Page 3 of 3

DIVISION OF MITIGATION SERVICES (DM'S)
IN -LIEU FEE REQUEST FORM Revised 4/23/2015
Complete requested information, sign and date, email to kellv.williamsftncdenr.aov. . Attachments are acceptable for clarification
purposes (location map, address or lat long is required). Information submitted is subject to NC Public Records Law and may be
requested by third parties, Review meetings are held on Tuesday afternoons. -
CONTACT INFORMATION APPLICANT'S AGENT APPLICANT
1. Business/Company Name Michael Baker Engineering, Inc. Piedmont Triad Airport Authority
2. Contact Person Richard Darling Alex Rosser, PE
3. Street Address or P O Box 5000 Regency Pkwy., Suite 600 1000-A Ted Johnson Pkwy.
4. City, State, Zip Cary, NC 27518 Greensboro, NC 27409
5. 919.4$1.57 Telephone Number --
- 40 336.665.5600
6. E -Mail Address [e-mail]
PROJECT INFORMATION
7. Project Name
8. Project Location (nearest town, city)
9. Lat-Long Coordinates or attach a map
10. County
11. River Basin & Cataloging Unit (8 -digit)
(See Note 1)
12. Project Type "*indicate owner type and
write in project type (e.g. school, church, retail,
residential, apartments, road, utilities, military,
etc.)**
13. Riparian Wetland Impact (ac.) (e.g., 0.13)
14. Non -Riparian Wetland Impact (ac.)
HAECO Facility Improvements
[e-mail]
Radar Road, Greensboro, NC 27410
36 05 49 N, 79 55 53 W
Guilford
Owner Type: ) Government 0 Private
Project Type: aviation development
0.81
C
15. Coastal Marsh Impact (ac.) 1 0
16. Stream Impact (ft.) (e.g. 1,234)
17. Riparian Buffer Impact (sq. ft.)
Include subwatershed if Jordan or Falls Lake:
18. Regulatory Agency Staff Contacts
USAGE. David Bailey
s
Warm. _ Cool Cold
1,601 i
Zone 1: Zone 2:
NCDWR:
Other: Sue Homewood
Check (�) below if this request is for a: By signing below, the applicant is confirming they ha)
revision to a current acceptance ! read and understand the DMS refund policy posted at
nceep.net and attached to this form.
renewal of an expired acceptance Signature f Ap cant or Authorized Agent:
extension of acceptance
unexpired
p
Date: 11(131 wtS
Note 1: For help in determining the Cataloging Unit, visit:www.nceeti.net or contact DMS
Direct questions to Felly Williams at 919-707-8915 or kellv.williamsCa)ncdenr.Qov or to the front desk at 919707-8976

Print Form
DMS ILF Mitigation Request Statement of Compliance with §143-214.11 & 143-214.20
(link to G.S. 143-214.11)
Prior to accessing the Division of Mitigation Services (DMS), all applicants must demonstrate compliance
with G.S. § 143-214.11 and 143-214.24. All requests MUST include this form signed and dated by the
permit applicant or an authorized agent. Please refer to DENR's Implementation Poli\ for more details.
Compliance Statement:
have read and understand G.S. § 143-214.11 and 214.20 and have, to the best of my
knowledge, complied with the requirements. I understand that participation in the DMS is
voluntary and subject to approval by permitting agencies.
Please check all that apply:
Applicant is a Federal or State Government Entity or a unit of local government
meeting the requirements set forth in G.S. 143-214.11 and is not required to
purchase credits from a mitigation bank.
ri There are no listed mitigation banks with the credit type I need located in the
hydrologic unit where this impact will take place (link to DwR list)
Mitigation bank(s) in the hydrologic unit where the impacts will occur have been
contacted and credits are not currently available.
® The DWR or the Corps of Engineers did not approve of the use of a mitigation
bank for the required compensatory mitigation for this project.
F7 This is a renewal request and the permit application is under review. Bank
credits were not available at the time the application was submitted.
Enter date permit application was submitted for review:
Note: It is the applicant's responsibility to document any inquiries made to private mitigation
banks regarding credit availability.
I have read and understand the DMS refund policies (attached)
ini1 bete
J. Alex Rosser, PE; Deputy Executive Director
Signature of Applicant or Agent Printed Name
Date
HAECO Facility Improvements
Piedmont Triad International Airport
Project Name Location

Refund Policv for Fees Paid to DMS In -Lieu Fee Proqrams (912112009)
Purpose: The purpose of this policy is to make clear the circumstances and process under which a
permittee can obtain a refund while simultaneously balancing customer service and responsible
business practices. This policy applies to all refund requests made on or after the publication date of
this policy.
Policy Statement: The policy of DMS is to allow for refunds under certain conditions.
1. All refund requests must be made in writing to the DMS In -Lieu Fee Program Coordinator at
kellv.wiIIiams(&ncden r.gov.
2. All refund requests are subject to fund availability. DMS does not guarantee fund availability for
any request.
3. The request must either come from the entity that made the payment or from an authorized agent.
Third parties requesting refunds must provide written authorization from the entity that made the
payment specifying the name and address of the authorized refund recipient.
4. Refund requests related to unintended overpayments, typographical errors or incorrect invoices
should be brought the attention of the In -Lieu Fee Program Coordinator as soon as possible. Such
requests are typically approved without delay.
S. Payments made under the incremental payment procedure are not eligible for refunds.
b. Refund requests made within nine months of payment to DMS will only be considered for requests
associated with projects that have been terminated or modified where the permittee's mitigation
requirements have been reduced. Such requests must be accompanied by written verification from the
permitting agency that the project has been cancelled, the permits have been rescinded or have been
modified, or the mitigation requirements have been reduced.
7. Refund requests made more than nine months from the payment date will only be considered for
permits that were terminated or modified to not require any mitigation. Such requests must be
accompanied by written verification from the permitting agency that the project has been cancelled, the
permits have been rescinded and/or mitigation is no longer required.
8. Refund requests not meeting the criteria specified above are not eligible for a refund.
9. Refund requests that meet the criteria above will be elevated to DMS Senior Management for
review. The following considerations apply to all refund requests:
a. availability of funds after consideration of all existing project and regulatory obligations
b. the date the payment was made
c. the likelihood DMS can use the mitigation procured using the payment to meet other
mitigation requirements
10. Once a refund has been approved, the refund recipient must provide a completed W-9 form to the
DMS In -Lieu fee Program Coordinator within two weeks in order to process the refund though the
State Controller's Office,
11. All decisions shall be final.

11/252015
W Shipment Receipt
Address Information
FedEx Shp Manager -Print Yotr Labels)
Ship to: Ship from:
David Bailey Phyllis Best
US Army Corps of Engineers Michael Baker Corp.
3331 Heritage Trade Dr. 8000 Regency Parkway
Suite 105 Suite 600
WAKE FOREST, NC Cary, NC
27587 27518
US US
919-554-4884 919-463-5488
Shipment Information:
Tracking no.: 775064672806
Ship date: 11/25/2015
Estimated shipping charges: 8.60
Package Information
Pricing option: FedEx Standard Rate
Service type: Priority Overnight
Package type: FedEx Pak
Number of packages: 1
Total weight: 1 LBS
Declared Value: 0.00 USD
Special Services:
Pickup/Drop-off: Use an already scheduled pickup at my location
Billing Information:
Bill transportation to: MICHAEL BAKER JR INC -994
Project Number: 148092
Task Number: I
Invoice no. :
Department no:
Thank you for shipping online with FedEx ShipManager at fedex.com.
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FedEx will host he responsible fa any clam in excess of $100 per package, whedw the result of loss, damage, delay, r delivery, misdelivery, or misinfamabon, unless ypu d8dwO a higher
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includirig intrinsic value of the package, loss of sales, income interest, profit attorney's fees, costs, and other forms of damage whether direct, incidental, consequential, a special is limited to the
greats of $100 or the aulMrized declared value. Recovery cannot exceed achsl documented loss. Maximum for items M extraadnary value is $1000, e.g., jewelry, precias metals, negotiable
imbUrnerlb and mhw items listed in err Service Gude. Written Gams must be filed within strict Uma limits; Casult the applicable FadEx Service Guide for details.
The estimated shipping charge may be different than the actual charges for your shipment. Differences may occur based m ache) weight dmensions, and ofactors. Consult the applicable
F_drx Service Guoe a the FedEx Rete Sheels for details on how stopping charges we calculated.
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11/25/2015
Wal,K _ Shipment Receipt
Address Information
Ship to:
Karen Higgins
NCDENR-DWQ 401
Permitting
512 Salisbury St.
Archdale Blding, 9th Floor
RALEIGH, NC
27604
US
919-807-6360
Fei Ship Manager -Print Your l.abel(s)
Ship from:
Phyllis Best
Michael Baker Corp.
8000 Regency Parkway
Suite 600
Cary, NC
27518
US
919-463-5488
Shipment Information:
Tracking no.: 775064584645
Ship date: 11/25/2015
Estimated shipping charges: 22.66
Package Information
Pricing option: FedEx Standard Rate
Service type: Priority Overnight
Package type: Your Packaging
Number of packages: 2
Total weight: 10 LBS
Declared Value: 0.00 USD
Special Services:
Pickup/Drop-off: Use an already scheduled pickup at my location
Billing Information:
Bill transportation to: MICHAEL BAKER JR INC -994
Project Number: 148092
Task Number: 1
Invoice no. :
Department no:
Thank you for shipping online with FedEx ShipManager at fedexxom.
Please Note
FedEx will not be respatsible for any claim in excess of $100 pr package, whether the result d loss, damage, delay, nondelivery, misdelivery, Or misinformation, unless you dedwe a Mgher
value, pay an atlbtod charge, doc mem yon actual loss and file a timely clam. Umitadms found in Vie currera FedEx Service Gude apply. Vora nigh m recover horn FedEx for arty loss,
including intrinsic valued the package. loss of sales, income interest, profit, adarnei fens, costs, and other forms of damage whether direct, incidental, consmtAritial, a special is limited to Via
greeter of $100 or the authorized declared value. Recovery cannot exceed actual documented lass. Maximum far items of immaodinary value is $1000, e.g., lerelry, precious metals, negotiable
instruments and ether items listed in our Service Gude. Written dams must be filed vaatn strict time limit,; Consult the applicable FedEx Service Guidsfor details.
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FedEx Service Guide a ore FedEx Rate Sheets for debut is on how shipping charges we calculated.
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