20050122 Ver 1_More Info Received_20140224

1616 East Mdlbrook Road, Suite 160
®ld®IR Raleigh, NC 27609 ! o�
m o f f a t t& n i c h o l (919) 781 -4626 Fax [phone]
www moffattnichol com
To: NCDENR – DEMLR- Stormwater Program
1617 Mall Service Center
Raleigh, NC 27699 -1617
Attn: Annette Lucas
Phone: [phone]
TRANSMITTAL
Date: 2/20/2014
Subject. Klldaire Farm Road BMP Modification
M&N Job No: 8355
Submittal No:
WE ARE SENDING YOU VIA: ❑ FedEx ® USPS ❑ Hand - Delivery
❑ Messenger ❑ Attached ❑ Other mall
❑ Shop Drawings ❑ Information ® Drawings ❑ Samples /Catalog Cuts
❑ Specifications ® Letters ❑ Change Order ❑ Other
Copies Description
1 Letter
1 Plan sheet
❑
For your use
®
For approval
❑ As requested
❑
Submit —copies for
For review and comment
El For Bids Due
distribution
❑
Return of corrected prints
❑
Resubmit —copies for
❑ Return of Loaned Items
approval
❑
Other
REMARKS-
cc
SIGNED Ryan A Smith
I vvFEB Ix WA7R UALITY
nd9 , _
If enclosures are not as noted, kindly notify us at once.

",IR
moffott & nchol
February 20, 2014
1616 East Millbrook Road, Suite 160
Raleigh, NC 27609
(919) 781 -4626 Fax [phone]
www moffattnichol com
N C Division of Energy, Mineral and Land Resources
1612 Mail Service Center
Raleigh, NC 27699 -1612
Attn Annette Lucas
Re: Kildaire Farm Road BMP Modification, Cary, NC
Ms Lucas
I am sending this letter at the request of the Town of Cary, NC The Town is currently responsible for the
maintenance of a stormwater BMP on the north -west side of Kildaire Farm Road, between Steep Bank
Drive and Loch Highlands Drive, adjacent to Hemlock Bluffs Nature Preserve Based on conversations
with the Town, our understanding is that the BMP is not being regulated by NCDENR, however the Town
has requested that this letter be sent for your information
The BMP was initially constructed In association with the widening of Kildaire Farm Road and was
designed to be a bioretention cell The BMP has subsequently become clogged and after extensive
investigation, the Town has determined that the most appropriate course of action is to convert the
bioretention cell into a stormwater wetland Our company reviewed the available original design
information, collected field measurements and has completed a design for the conversion to a wetland
(plan sheet enclosed)
The first flush runoff volume from the 1 -inch rainfall was calculated, based upon information from the
original design received from the Town, to ensure that it could be captured by the modified system The
first flush volume calculated was 2990 cubic feet and the calculated storage volume in the new system
was 3230 cubic feet Additionally, in the original plan the water quality storage took place between
elevations 409 8 feet and 410 5 feet and in the modified system the water quality storage will take place
between elevations 409 9 feet and 410 6 feet We are maintaining the original ponding depth of 0 7 feet,
yet 0 1 feet higher within the same basin, which technically results a larger water quality storage volume
than the original design
A simple XPSWMM model was used to evaluate the hydraulics of the new system We used the model to
verify that the wetland outlet structure would draw the water surface back to the normal pool elevation in 2
to 5 days and to size the primary weir structure to pass the 10 -year storm peak flow (8 6 cfs, from the
original design) without activating the secondary overflow berm (shown on the enclosed plan sheet, on
the east side of the wetland)
Please contact us if you any concerns or need for additional information about the project
Sincerely,
C aRo
��p ESS•.!�%
2•�3 01
Moffatt & Nichol
yam;
SEAL
032731
Ryan A Smith, PE
Encl Graphics from the XPSWMM model (3 pages) '/ /1 I SI \ \ \V ° ---- -- �(J r(��
Kildaire Farm Road BMP Modification plan (1 sheet) D �����L�t fi
Tou^ CuNi6iLi .S Carolyn Lew,$ - ylq- 46y -Y36Z i ,.
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