20180134 Ver 1_More Info Received_20181115

Strickland, Bev
From:
Jeffrey Brown <[e-mail]>
Sent:
Thursday, November 15, 2018 5:21 PM
To:
Amschler, Crystal C SAW
Cc:
Corey Knox; Tate, Knox; Homewood, Sue
Subject:
[External] Re: [Non-DoD Source] Lake Tahoma Dredge
. • • • •. ernal email. Do not click links or open attachments unless verified. Send all suspicious email as an attachment to
Crystal, please find my answers below in blue.
Jeffrey,
Thank you for this information. This pretty much satisfies what I need to process the permit with just some
clarification needed after reviewing your response to the comments.
One of the concerns with lowering the lake is that sediment could be released downstream. You've addressed
the potential for sediment released at the dredge sites, but there is also the risk that sediment has accumulated
behind the dam, and that when the lake is lowered though the penstock, accumulated sediment could be
released to downstream waters at that time. Please address the potential for sediment to be released when
the penstock is opened to lower the lake and indicate any measures that will be taken to prevent this from
happening. Has there been, or could there be measurements taken at the dam site to determine if sediment
has accumulated behind the dam?
There is very to none — in the risk of sediment accumulated behind the dam to be released downstream. First,
the penstock is only 15 feet below the Lake pool elevation — and is operated in a fashion as to where the intake
side of the penstock remains free and clear of debris/siltation. The bulk of sediment build up is near the base of
the dam just below the Spillway opening. At the base of the Dam there is a 24 -inch valve. The 24 -inch control
valve at the base of the DAM is FROZEN. NCDEQ required Buck Creek to close it permanently as to reduce
ANY risk of down stream sediment.
Lastly, you've indicated that when the lake is lowered it will flow at an average of 103 CFS (approximately 66.6
mgd). For comparison, please indicate the current outflow rate, in mgd, that occurs at normal lake
levels. Additionally, please indicate how the lake will be refilled and what the outflow during refill will be to
ensure that the minimum of 3 mgd's requested by the City of Marion will be maintained.

Those are normal flows. The DAM is a RUN of the River Dam - The spillway cannot be raised, lowered,
closed, etc. It is a static opening with a capacity of 11,360 CFS.
It takes approx. 10 days to lower the lake 15 ft. It takes approximately the same time to fill, given that when
Lake Tahoma is refilled the penstock is closed half- full, which allows 40-55 CFS (this is based on head of lake
obviously) — insuring downstream flow and filling of the Lake.
Filling the lake has never been the issue, the issue has been keeping it lowered because the amount of flow
into the Lake. A 5-10 year storm can fill the Lake in an afternoon.
I'm currently working on the decision document for the proposed project and will continue to do so, and
incorporate the above requested information, to complete the final draft of the decision document in the coming
weeks. Once all the other approvals are received, the next step will be to finalize the decision document and
draft the permit for issuance and send the permit to the applicant for review.
Sincerely,
Crystal C. Amschler
Project Manager
Asheville Regulatory Field Office
151 Patton Avenue, Room 208
Asheville, NC 28403
(828)-271-7980 Ext 4231
The Wilmington District is committed to providing the highest level of support to the public. To help us ensure
we continue to do so, please complete the Customer Satisfaction Survey located at:
http://corpsmapu.usace.army.miIlcm apex/f?p=136:4:0
On Thu, Nov 15, 2018 at 4:54 PM Amschler, Crystal C CIV USARMY CESAW (US) <[e-mail]>
wrote:
Jeffrey,
Thank you for this information. This pretty much satisfies what I need to process the permit with just some clarification
needed after reviewing your response to the comments.
One of the concerns with lowering the lake is that sediment could be released downstream. You've addressed the
potential for sediment released at the dredge sites, but there is also the risk that sediment has accumulated behind the
dam, and that when the lake is lowered though the penstock, accumulated sediment could be released to downstream
waters at that time. Please address the potential for sediment to be released when the penstock is opened to lower
the lake, and indicate any measures that will be taken to prevent this from happening. Has there been, or could there
be measurements taken at the dam site to determine if sediment has accumulated behind the dam?
Lastly, you've indicated that when the lake is lowered it will flow at an average of 103 CFS (approximately 66.6
mgd). For comparison, please indicate the current outflow rate, in mgd, that occurs at normal lake levels. Additionally,

please indicate how the lake will be refilled and what the outflow during refill will be to ensure that the minimum of 3
mgd's requested by the City of Marion will be maintained.
I'm currently working on the decision document for the proposed project and will continue to do so, and incorporate
the above requested information, to complete the final draft of the decision document in the coming weeks. Once all
the other approvals are received, the next step will be to finalize the decision document and draft the permit for
issuance and send the premti to the applicant for review.
Sincerely,
Crystal C. Amschler
Project Manager
Asheville Regulatory Field Office
151 Patton Avenue, Room 208
Asheville, NC 28403
(828)-271-7980 Ext 4231
The Wilmington District is committed to providing the highest level of support to the public. To help us ensure we
continue to do so, please complete the Customer Satisfaction Survey located at:
http://corpsmapu.usace.army.mil/cm apex/f?p=136:4:0
-----Original Message -----
From: Jeffrey Brown [mailto:[e-mail]]
Sent: Friday, November 9, 2018 3:09 PM
To: Amschler, Crystal C CIV USARMY CESAW (US) <[e-mail]>; Corey Knox
<corev@brown Pa.net>
Cc: Tate, Knox <[e-mail]>
Subject: [Non-DoD Source] Lake Tahoma Dredge
Crystal,
please find the attached information, per your request.
If you have any questions, please let me know.
Jeffrey