Permanent Dam Safety Modification at Cherokee, Fort Loudoun, Tellico, and Watts Bar Dams, TN

AGENCY:

Tennessee Valley Authority.

ACTION:

Notice of intent.

SUMMARY:

This notice is provided in accordance with the Council on Environmental Quality's regulations (40 CFR parts 1500 to 1508) and Tennessee Valley Authority's (TVA) procedures for implementing the National Environmental Policy Act (NEPA). TVA will prepare an environmental review (in the form of an environmental assessment [EA] or an environmental impact statement [EIS]) to address the potential impacts to the natural, physical, and human environment resulting from various alternatives for permanent modifications to the existing dam facilities at Cherokee, Fort Loudoun, Tellico, and Watts Bar dams in Tennessee. The level of review will be determined after the public scoping process has been completed. TVA is evaluating long-term permanent solutions for dam safety modifications to replace interim modifications that were implemented at the dams.

DATES:

To ensure consideration, comments on the scope of the environmental issues must be postmarked or e-mailed no later than August 5, 2011. When a draft environmental review (either an EA or EIS) is prepared, it will be made available for public review.

ADDRESSES:

Written comments should be sent to Kenneth P. Parr, NEPA Specialist, NEPA Compliance, Environmental Permits and Compliance, Tennessee Valley Authority, 1101 Market Street (LP 5U), Chattanooga, Tennessee 37402-2801. Comments may be e-mailed to kpparr@tva.gov, submitted by fax to 423-751-3230, or entered online at http//www.tva.com/environment/reports/index.htm.

FOR FURTHER INFORMATION CONTACT:

David Lane, Environmental Engineer, Tennessee Valley Authority, 400 West Summit Hill Drive (GRN 2E), Knoxville, Tennessee, 37902-1499; e-mail: jdlane@tva.gov.

SUPPLEMENTARY INFORMATION:

Background

TVA evaluates its dam safety program regularly (especially as technology and standards evolve and when more or better data become available) and modifies its dams as needed to ensure the structural integrity of TVA dams and the safety of the public. Periodic updates regarding maximum flood conditions are conducted when parameters used in flood modeling change, e.g., probable maximum precipitation or river operation guidelines. TVA assumes the most extreme weather event reasonably possible when determining maximum flood conditions of the river system. TVA's most recent probable maximum flood calculations indicate that a worst-case winter storm could cause water to go over the top of some dams even with the floodgates wide open, possibly causing dam failure. Failure of any dam would result in loss of stored water for navigation, impacts to fish and wildlife resources, loss of recreational opportunities, and possible property damage, personal injury, and loss of life. Failure also could result in failures to downstream dams.

To minimize the potential effects of a severe flooding event predicted by revised probable maximum flood modeling, precautionary measures have been implemented on top of the earth embankments at four (Cherokee, Fort Loudoun, Tellico, and Watts Bar) dams. These measures included raising dam elevations about 3 to 4 feet by placing interconnected, fabric-lined, sand-filled HESCO containers in order to safely pass predicted worst-case floodwaters, to avoid dam overtopping and possible impacts to the downstream embankment, and to provide additional floodwater storage capacity. The downstream embankment of Watts Bar Dam has also been strengthened with concrete matting.

TVA must now develop permanent solutions for the precautionary measures that were put in place to correct safety deficiencies identified at Cherokee, Fort Loudoun, Tellico and Watts Bar dams. The need for the proposed action is to prevent the impacts associated with dam failure. TVA has developed alternatives that consider the level of risk reduction to the public, constructability, potential environmental impacts, and cost.

Proposed Alternatives

TVA has performed preliminary internal scoping and identified a No Action Alternative and two Action Alternatives: permanent modifications to dam structures and removal of the temporary HESCO baskets before the end of their useful life.

The No Action Alternative is the current existing condition at the Cherokee, Fort Loudoun, Tellico, and Watts Bar dam sites. A permanent concrete mat structure has been installed in the downstream embankment of Watts Bar Dam, and HESCO baskets have been installed at Cherokee, Fort Loudoun, Tellico, and Watts Bar dams. These items would remain in place and would be maintained as needed. These temporary measures were installed to prevent floodwaters from potentially overtopping the dams and to ensure the integrity of the downstream embankments, thus increasing the public safety of downstream residents and the safety of TVA's critical nuclear facility operations.

Under the first Action Alternative, the HESCO baskets would be replaced, and permanent dam modifications would be made to each of the four dam structures. The potential modifications could include construction of concrete floodwalls, raising of earth embankments, or a combination of floodwalls and raised earth embankments. The permanent concrete mat structure in the downstream embankment of Watts Bar Dam would remain in place. Under this alternative, the potential for overtopping of the dams during a probable maximum flood event would be prevented. This would ensure that the integrity of the downstream embankments would be maintained and thereby increase the public safety of downstream residents and the safety of TVA's critical nuclear facilities.

Under the second Action Alternative, TVA would consider removal of the temporary HESCO baskets from the dam structures before the end of their useful life. The permanent concrete mat structure installed in the downstream embankment of Watts Bar Dam would remain. This alternative is similar to the situation at the dams prior to placing the HESCO baskets on the dams as an interim solution for management of the potential maximum flood events. Under this alternative, overtopping of the dams would be possible during a very low-risk probable maximum flood event. The downstream integrity of the dam embankments could be compromised, thus jeopardizing the public safety of downstream residents and the safety of TVA's critical facilities. The analysis of this alternative would contain a discussion/justification regarding the reasons for placing the baskets on top of the dams to address this low-risk event.

Proposed Issues To Be Addressed

The environmental review will contain descriptions of the existing environmental and socioeconomic resources within the area that would be affected by construction, operation, and maintenance of the proposed permanent dam modifications. Evaluation of potential environmental impacts to these resources will include, but will not necessarily be limited to, the potential impacts on water quality, aquatic and terrestrial ecology, endangered and threatened species, wetlands, aesthetics and visual resources, recreation, land use, historic and archaeological resources, and socioeconomic resources. The need and purpose of the project will be described. The final range of issues to be addressed in the environmental review will be determined, in part, from scoping comments. The preliminary identification of reasonable alternatives and environmental issues in this notice is not meant to be exhaustive or final.

Public and Agency Participation

The environmental review is being prepared to inform decision makers and the public about the potential environmental effects of TVA's options for minimizing the potential effects of a severe flooding event predicted by revised probable maximum flood modeling. The draft EA or EIS is anticipated to be available in late summer 2011. Any changes to this schedule will be posted on the TVA Web site: http://www.tva.com/environment/reports/index.htm. The environmental review process will also serve to inform the public and the decision makers of the reasonable measures that would be implemented to minimize adverse impacts. Other Federal, state, and local agencies and governmental entities are invited to provide scoping comments. These agencies include, but are not limited to, the U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, Tennessee Department of Environment and Conservation, and the Tennessee State Historic Preservation Officer.

The public is invited to submit comments on the scope of the environmental review no later than the date given under the DATES section of this notice. TVA will conduct an additional public review after the draft EA or EIS is prepared.