20121049 Ver 1_More Info Received_20130603

Strickland Bev
From: [e-mail]
Sent Monday, June O3.2O135:48PK4
To: Lucas, Annette; Stu Henry
Cc: Chris Unnberger; Honnewood, Sue; Sthok|ond, Bev; Alex Rosser(RossenA@gsooicorg); Lorry
Allen
Subject: RE: Honda K4RO Facility Detention
Annette,
Here isapdfof the Addendum that vve have been discussing. | have also included a copy of the revised drawing [2.55
that describes the modifications from a sediment basin to the detention basin. This is where vve have added the use of
native grasses for the basin in lieu of the fescue previously specified. VVe have talked with a nursery regarding these
mixtures and they should be suited for the intended use in the frequently saturated zones and the remainder of the
basin wall areas. These species do not have flowers nor are likely to attract waterfowl or birds. | will submit the hard
copies by overnight FedEx tomorrow for Wednesday delivery.
Please let me know if there is anything else vve should supply.
Thanks again for all your assistance,
Ed McHugh. PE | Project Engineer | Barge Waggoner Sumner & Cannon. Inc.
1n1oo Sherri nawu, Suite cnn Knoxville, Two7eoc|aas.aoT.umu -Office | 865.599.3924 -Mobile
From: Lucas Annette[maiKo:annetteJucas@ncdenr.00v]
Sent: Sunday, ]uneO2,2O1]9:27PM
To: Stu Henry
Cm: Ed McHugh; ChrisUmbenger; Homewood, Sue; Strickland, Bev
Subject: RE: Honda MRO Facility Detention
This all sounds fine. Can you please submit the information to the address below for my formal review? We need one
hard copy of the information and one disk with all the information in pdf.
Thanks,
Annette
Annette M. Lucas, PE
Environmental Engineer
lVCI}IClVR I DW() I Wetlands and BtorcuwaterBranch
I85O Mail Service Center, Raleigh, lVC278QQI85O(D�ail)
512 N. Salisbury St, Raleigh, NC 27804 1 Q'u Floor (.Looatiora 8n Parcels)
Phone: (QIQ)8O7-838I 1 Fax: (QIQ)8O7-84Q4 1 Email:
Weboite:
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E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be disclosed to
third parties.
From: Stu Henry[[e-mail]
Sent: Thursday, May 30, 2O1]4:16 PM
To: Lucas, Annette
Cm: Ed McHugh; Chris Umberoer
Subject: RE: Honda MRO Facility Detention

Here is the recommendation for the plant mix;
Selecting a plant type that both handles the periodic moisture associated with a storm water detention basin, without
creating wildlife habitat as discouraged by the FAA regulations is a challenge. The following plant types would be
potential options, as they are lower growing, and mostly seed free, which should be a minimal attraction to surrounding
bird populations.
Please let us know if there are any additional recommendations or comments from your folks.
Stu
From: Lucas, Annette
Sent: Thursday, May ]O,2O1]2:O1IPM
To: Stu Henry
Cm: Ed McHugh; ChrisUmbenger
Subject: RE: Honda MRO Facility Detention
Stu,
Soit looks like about a 5O/5O split between infiltration and surface flow. What did you find out about vegetating the
invert of the basin?
Annette
From: Stu Henry
Sent: Thursday, May 30, 2013 12:14 IPM
To: Lucas, Annette
Cm: Ed McHugh; Chris Umberoer
Subject: Honda MRO Facility Detention
Ed asked that I forward this to you as a draft to see if it satisfied your comments.
Please feel free to contact Ed or myself if any further questions were generated.
Stu
PEI

Stuart N. Henry, P.E.
Vice President
BWSC
[phone] office
[phone] fax
[e-mail]
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ADDENDUM TO
CONSTRUCTION f , TER
DETENTION POND CALCULATIONS

•
6430 Ballinger Road
Greensboro,

The purpose of this addendum is to provide calculations showing the anticipated
infiltration capacity of the detention pond area at the east corner of the site along
Chimney Rock Road.
SUMMARY OF CALCULATIONS
Existing Conditions
The existing site conditions were determined from a site aerial survey from the Piedmont
Triad International Airport Authority (PTAA) and supplied to BWSC by the developer.
The approximately 62.73 acre total site is a previously undeveloped lease parcel owned
by the PTAA that is southeast of and immediately adjacent to the Piedmont Triad
International Airport. The site was previously used as pasture, forest, and low - density
residential development. Soils map information was obtained on -line from the U.S.
Department of Agriculture, Natural Resources Conservation Service web soil survey web
site ( http : / /websoilsurvey.nres.usda. 4ov /app /WebSoilSurvey.asox). A copy of the soils
mapping is included. The soil survey shows primarily sandy clay loams.
Proposed Conditions
The site is proposed to be used as an aircraft maintenance facility. The current planned
facility will contain offices and hangar bays for aircraft maintenance. The current grading
plan directs approximately 35.67 acres of the developed site to the detention pond at the
east corner of the site along Chimney Rock Road. This portion of the facility has an
estimated area - weighted SCS curve number of 85 after full build -out.
The previous detention calculations showed that the calculated post- development
condition peak flows at the pond outfall will be less than the calculated pre- development
flows for the reviewed storm events. Those calculations included runoff and routing
calculations for the 1" rainfall event to show the expected performance of the pond.
These computations did not include an estimate for infiltration of stormwater into the
pond bottom.
1

Methods and Assumptions
The hydrology and hydraulics for the area draining to the pond were simulated in the
Bentley CivilStorm software, V8i Edition. An SCS approach was used for the curve
numbers and times of concentration and 24 -hour, Type II, SCS storm events were used.
All catch basins were assumed to be full capture type with no bypass assumed. Structure
head losses were calculated using a HEC -22 approach. The detention pond was designed
as a dry pond in order to avoid classification by the Federal Aviation Administration as a
hazardous wildlife attractant (Section 3, FAA Advisory Circular AC No. 150/5200 -33)
and the resulting wildlife hazard mitigation techniques.
The NRCS soils data for the estimated saturated hydraulic conductivity were used and are
included. The NRCS soils data shows the expected soils in the pond area as
Mecklenburg sandy clay loam types with an area along the north property line of Poplar
Forest clay loam. Since the Mecklenburg clay loam is shown as to be the predominant
type for that area and had the lowest saturated hydraulic conductivity rating, this value
was conservatively used for the saturated hydraulic conductivity rating of the entire pond.
The saturated hydraulic conductivity reported by the NRCS was 5.1527 µm/s.
Conversion of this value to English units produces a value of 0.73 inches /hour which was
input to CivilStorm as an average infiltration value. All other inputs for the site drainage
were as described in the main calculation.
Average residence times were calculated for the pond at each time step. A triangular
profile was assumed for the stored flow radially out from the outlet structure. Therefore,
the average depth was calculated by dividing the depth at the outlet structure in half. An
average cross section width of 200 feet was measured from the plans, and the flow
velocity was then calculated by definition as flow divided by cross section width
multiplied by average depth. A plug flow condition was assumed due to the rock check
dam and low outlet flows. Therefore, the distance of the center of the triangular storage
profile was calculated as the water depth divided by the 1% slope multiplied by a factor
of three. The residence time was then calculated at each time step as the center of mass
distance divided by the velocity.
2

Pond Results
A graph of the CivilStorm results is included showing the pond hydraulic grade line
elevation, the total flow rate out, flow rate out of the pond through the outlet structure,
flow rate out for infiltration, and storage volume over the simulation time. A second
graph shows the runoff cumulative volumes over time comparing the pond inflow against
the outflow with the average residence time plotted on a secondary axis.
Review of the volume graph shows that the expected soil infiltration is approximately
48% of the total volume with 52% released from the outlet structure. Note that to
improve stability, the CivilStorm program does not preserve volume when the run is
extended in time. Therefore, the inflow at the end of the storm event continues at a
constant rate resulting in increasing volumes without additional rainfall. However, it can
be seen that the graphs stabilize to a constant outflow rate at about 36 hours (2,160
minutes), 12 hours after rainfall cessation. This can be assumed as the point where the
pond is empty, meeting the requirements for complete pond drawdown within 72 hours.
Inspection of the residence time graph shows some noise in the data. However, the
general residence time can be seen to increase as storage is filled and decrease as drain
down occurs. Calculations show a maximum residence time of about 9.5 hours,
minimum of 0.42 hours and an average of 4.14 hours.
9

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