[Federal Register Volume 83, Number 77 (Friday, April 20, 2018)]
[Notices]
[Pages 17541-17542]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-08291]
-----------------------------------------------------------------------
DEPARTMENT OF THE DEFENSE
Department of the Army, Corps of Engineers
Intent To Prepare a Draft Environmental Impact Statement for the
Dam Safety Modification Study Report for Center Hill Dam, DeKalb
County, Tennessee
AGENCY: U.S. Army Corps of Engineers, DoD.
ACTION: Notice of Intent.
-----------------------------------------------------------------------
SUMMARY: Pursuant to the National Environmental Policy Act (NEPA) of
1969, as amended, the U.S. Army Corps of Engineers, Nashville District
(USACE) is preparing a draft Environmental Impact Statement (EIS) to
support the Dam Safety Modification Study Report (DSMSR) for Center
Hill Dam. The study would evaluate the main dam spillway gate
operability, the saddle dam fuse plug operation, and spillway additions
to the new Roller Compacted Concrete (RCC) berm structure at the saddle
dam, all for the purpose of lowering risk at Center Hill Dam, DeKalb
County, Tennessee.
DATES: Comments regarding the NOI must be received by USACE within 30
days of publication of the NOI on or before May 20, 2018.
ADDRESSES: USACE-Nashville District, 110 9th Avenue South, RM 405A,
Nashville, Tennessee 37203-3817.
FOR FURTHER INFORMATION CONTACT: Please direct your comments to Joy
Broach, Aquatic Biologist, (615) 736-7956; email:
[email protected]. Written comments can be mailed to the
address above.
SUPPLEMENTARY INFORMATION: 1. Background Information. Center Hill Dam
was designed in the 1930s, constructed in the 1940s, and impounded in
the early 1950s. The dam was built on karst geology using accepted
engineering practices of the day. Center Hill Dam consists of a 248'
high by 1,400' long combination earthen embankment and concrete main
dam, and a 125' high by 800' long earthen embankment auxiliary dam
referred to as the saddle dam. The main dam has eight 34' x 57'
spillway gates that rotate upward to safely pass flow during and after
large rainfall events. To comply with updated design flood guidance, a
self-eroding fuse plug section was retrofitted into the top of the
saddle dam in 1992 to serve as an emergency spillway. The fuse plug
operation almost doubles Center Hill's total spillway capacity to keep
the main dam from overtopping during an extreme flood event. A Dam
Safety Modification Study to reduce the risk of a foundation seepage
dam failure was approved in late 2006 and consisted of three major
construction contracts beginning in 2008. The first contract injected
concrete grout into the foundation of the main dam embankment (soil
portion of the dam) and was completed in 2010. The second contract
installed a concrete barrier wall into the main dam embankment and was
completed in 2015. This concrete barrier wall is the permanent seepage
barrier protection for the main dam embankment. The third major
contract for construction of a Roller Compacted Concrete (RCC) berm
below the saddle dam began in September 2016 and is on-going. The
purpose of the RCC berm is to reduce the risk of saddle dam failure
caused by under-seepage or overtopping during an extreme flood event. A
Post Implementation Evaluation (PIE) was completed in 2017 to assess
the effectiveness of the above construction
[[Page 17542]]
efforts to reduce the risk of dam failure. During the PIE, additional
risk issues were noted concerning the 70-year old main dam spillway
gates. Electrical, mechanical and structural operability issues affect
the reliability of controlled spillway releases. If the spillway gates
do not reliably operate during an extreme flood event, the reservoir
would raise and potentially result in a premature fuse plug operation.
The fuse plug is designed to discharge approximately 400,000 cubic feet
per second within 30 minutes. The consequences of premature discharge
of an enormous volume of flood water are estimated to be above the
Corps of Engineer's tolerable risk limit. The draft EIS would address
the findings of the PIE and assess effectiveness of potential
alternatives to further reduce risk and increase dam safety. The dam
seepage repair construction contracts noted previously, have increased
dam safety and were covered under previous NEPA documents.
2. Potential Alternatives. The draft EIS would address an array of
alternatives that could reduce the risk of life loss, extensive
downstream damage, functional loss of the project, and the loss of
project benefits. The nature and extent of the alternatives would be
determined based on the results of on-going engineering studies, public
and agency input during the scoping period, and preparation of the
draft EIS. Alternatives, either individually or in combination, that
have potential to affect structures or operations of the dam may
include the following:
a. Replacement of the current gate machinery with hydraulic
machinery that can operate under water;
b. Addition of equipment to the current spillway gates to keep them
open if the operating machinery is underwater;
c. Modification of the spillway gates or gate machinery to allow
operation from the top of the dam;
d. Relocation of the gate operating machinery to the road level,
which would require raising or relocating Highway 96 which currently
crosses over the dam;
e. Removal of the existing fuse plug at the saddle dam and
installation of spillway additions on top of the newly constructed RCC
Berm to discharge flood water down the valley;
f. Modification of the emergency operations plan in the water
control manual that determines how to manage floods at Center Hill Dam;
and
g. Other alternatives as identified by on-going engineering
studies, the public, and agencies.
3. Issues To Be Addressed. USACE is evaluating ways of raising,
modifying, and/or replacing existing spillway gates and operating
equipment to address spillway gate reliability for all range of
possible flood events, especially large and more extreme flood events.
The DSMSR and draft EIS would evaluate the Center Hill Dam Water
Control Manual emergency operating procedures and potential alternative
spillway options to determine if changes are warranted to minimize
overall dam safety risk. The draft EIS would include, but is not
limited to identification and evaluation of effects to aquatic and
terrestrial habitats, cultural resources, state and federally listed
species, socioeconomics, public safety, structures, hydrology and
hydraulics, recreation, water supply, water quality, flood storage,
hydropower production, land use, visual and aesthetic resources, and
dam safety risk reduction at Center Hill Dam as a result of the
proposed alternatives.
4. Public Involvement and Scoping. This NOI serves as the initial
step to involve Federal and state agencies, Indian Tribes, local
governments, and the public in an early and transparent process in
accordance with NEPA requirements. The draft EIS would address impacts
to the human environment due to the proposed alternatives. Concerns
would be identified based on public and agency input during the scoping
process and during preparation of the draft EIS. All interested parties
are encouraged to submit their name and email address to the address
noted above, to be placed on the project mailing list to receive fact
sheets, newsletters and related public notices. All interested parties
are invited to identify issues that should be addressed in the draft
EIS. A scoping meeting is scheduled for May 3, 2018 from 6:00-8:00 p.m.
at The Buffalo Valley Community Center, 2717 Buffalo Valley School
Road, Buffalo Valley, Tennessee. The purpose of the public scoping
meeting is to present information to the public regarding potential
alternatives that would be addressed in the draft EIS, receive public
comments, and to solicit input regarding dam safety concerns,
alternatives to consider, and environmental or social issues of concern
to the public.
6. Availability of the Draft EIS. USACE intends to circulate the
draft EIS in the late 2018/early 2019 time frame. USACE will announce
availability of the draft EIS in the Federal Register and other media,
and will provide interested parties an opportunity to submit comments
to be addressed in the final EIS.
Dated: April 13, 2018.
Angela E. Dunn,
Project Planning Branch Chief, U.S. Army Corps of Engineers, Nashville
District.
[FR Doc. 2018-08291 Filed 4-19-18; 8:45 am]
BILLING CODE 3720-58-P