83 FR 17541 - Intent To Prepare a Draft Environmental Impact Statement for the Dam Safety Modification Study Report for Center Hill Dam, DeKalb County, Tennessee

DEPARTMENT OF THE DEFENSE
Department of the Army, Corps of Engineers

Federal Register Volume 83, Issue 77 (April 20, 2018)

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.

[Federal Register Volume 83, Number 77 (Friday, April 20, 2018)]
[Notices]
[Pages 17541-17542]
From the Federal Register Online  [www.thefederalregister.org]
[FR Doc No: 2018-08291]


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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.

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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