20191641 Ver 1_Stream Profile_20200504

Strickland, Bev
From: Nagy, Eric <[e-mail]>
Sent: Monday, May 4, 2020 2:21 PM
To: Wojoski, Paul A
Cc: Mangas, Jeffrey; Harrison, Trevor
Subject: RE: [External] Reggie Jackson Airport Honda - Zone 1 Buffer Impact Change
Attachments: 2020-05-01 Stream Profile.pdf
External email. Do not click links or open attachments unless you verify. Send all suspicious email as an attachment to
iflp'[e-mail]
Hi Paul,
Attached is a plan view and profile of the redesigned bypass system. From our HECRAS model, the existing 100-yr flow
rate to the existing 38"x60" downstream culvert is 182.92 cfs, whereas the proposed 100-yr flow rate is reduced to
166.78 cfs. Therefore, we are not creating a more erosive flow rate to the 104 linear foot of avoided stream segment
with this development. The rip rap apron at the outlet is sized based on the attached NCDOT standard detail which sizes
the rip rap based on an assumed flow for a specified pipe size. The apron width was increased due to the 2nd 48" pipe
being added rather than an increase in flow.
The stream segment proposed to be impacted by the rip -rap was already counted as a loss. There are no increases to
the length of the rip rap apron from the original design, only the width of the rip rap apron. This increases the proposed
buffer impacts but not the proposed stream impacts. The proposed rip rap will be placed at existing grade. Since the
stream banks are currently vertical they may need to be laid back before placing the rip rap. The rip rap will be placed
within the current stream channel by over excavating the bottom of the stream and backfilling with the rip rap.
Additionally, the reason for the increase in the bypass pipe size from the previous design is based on providing
additional storage volume rather than a need to pass additional flow through the system. In the existing condition, the
stream is able to "back up" in high storm events that can't pass through the existing 38"x60" pipe. The additional
volume provided in the larger bypass pipe is being used to serve this same function in the proposed condition,
preventing an increase in the flood elevations on the adjacent property. The site will be meeting the diffuse -flow
requirements by meeting the 30% TN removal requirement for added on -site impervious area via the underground
detention and sand filter system. There are no changes to the water quality draining from the adjacent properties and
passing through the bypass system, therefore added water quality treatment is not required or provided for the bypass
system.
Please let us know if you have any further questions. Much appreciated,
Eric Nagy
Senior Environmental Scientist
EMH&T Engineers, Surveyors, Planners, Scientists
5500 New Albany Road, Columbus, OH 43054
v.614.775.4518 1 f.614.775.4802 1 ENagy<a?emht.com
emht.com femht.coml
From: Wojoski, Paul A <[e-mail]>
Sent: Sunday, April 26, 2020 1:25 PM
To: Nagy, Eric <[e-mail]>

Cc: Mangas, Jeffrey <[e-mail]>; Harrison, Trevor <[e-mail]>
Subject: RE: [External] Reggie Jackson Airport Honda - Zone 1 Buffer Impact Change
Hi Eric —
Yes, I am in receipt of Jeff's email and lease information — thank you, Jeff.
Regarding the prosed storm sewer bypass redesign — I have some questions and comments, outlined below.
Can you provide a design detail showing the discharge point for the outlet and associated rip -rap highlighting the
impacts to the bed, bank and riparian buffer? The footprint exhibits you provided are helpful, but the design raises
questions about stream impacts and meeting the diffuse flow -requirement in the buffer rules, therefore a side profile
drawing would provide more clarity. Will the bed and banks be re-graded/laid-back? Also, the stream segment which is
proposed to be impacted by rip -rap was already counted as loss, correct?
As I understand the design, during larger storm events the outlet pipe at the headwall will be carrying stormwater from
the sand filter SCM and the on -site by-pass combined with the larger duel 48" pipe off -site by-pass and discharge onto a
rip -rap pad that will cover the stream bed, bank and some of Zone 1 riparian area. This design and increased rip -rapped
dissipater area in the buffer to accommodate the larger bypass culverts brings up concerns regarding the destabilization
of this southeast stream segment (104 LF) as outlined in our January 24, 2020 letter. I'm having our stormwater engineer
review the project modifications, but any information or comments to help understand the design and address these
concerns they would be welcome.
Thanks,
Paul
Paul Wojoski
401 & Buffer Permitting Branch Supervisor
Division of Water Resources
Department of Environmental Quality
[phone] office
[e-mail]
512 N. Salisbury Street (Archdale Building), Suite 942-F, Raleigh, NC 27604
1617 Mail Service Center, Raleigh, NC 27699-1617
Email correspondence to and from this address is subject to the
North Carolina Public Records Law and may be disclosed to third parties.
From: Nagy, Eric [mailto:[e-mail]]
Sent: Tuesday, April 21, 2020 10:47 PM
To: Wojoski, Paul A
Cc: Mangas, Jeffrey; Harrison, Trevor
Subject: [External] Reggie Jackson Airport Honda - Zone 1 Buffer Impact Change
External email. Do not click links or open attachments unless you verify. Send all suspicious email as an attachment to
[e-mail]
Hi Paul,

I'm sure that by now you saw Jeff Mangas' email concerning the letter from the Raleigh Durham Airport supporting a
lease to Hendrick Automotive Group for the proposed project. Hopefully this will allow you to move forward with your
review.
There is one other change that occurred recently. As our engineers worked through the stormwater design, they
realized they needed a wider rip -rap apron at the end of the proposed culvert design. Based on additional stormwater
modeling, the engineers were required to increase the size of the bypass storm sewer pipe in order to avoid causing a
flood elevation rise on the upstream adjacent parcels. After revising the bypass storm sewer design, the outlet pipe was
changed from a single 48" pipe to a dual 48" pipe. The additional width of having a second outlet pipe required a wider
rip -rap apron. The wider rip -rap apron does not add stream impacts or Zone 2 buffer zone impacts past what was
previously requested. However, it does increase the amount of Zone 1 impact needed to 20,592 square feet. This change
will increase the Zone 1 impact by 319 square feet. The attached exhibits show this proposed change to the rip -rap
apron.
The increase in the amount of Zone 1 Buffer Impacts would increase the amount of required mitigation to for Zone 1 to
61,776 square feet. The total buffer mitigation required will now equal 85,928 square feet. The buffer mitigation is
proposed to be accomplished by purchasing from an accredited mitigation bank that services this watershed.
Please let me know if you have any questions about the above description or require further information.
Much appreciated,
Eric Nagy
Senior Environmental Scientist
EMH&T Engineers, Surveyors, Planners, Scientists
5500 New Albany Road, Columbus, OH 43054
v. 614.775.4518 1 f. 614.775.4802 1 [e-mail]
emht.com femht.coml fclicktime.symantec.coml

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May 1, 2020
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JOB NO.
20191012
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