E7-18146. Bear Creek Dam Leakage Resolution Project, Franklin County, AL

AGENCY:

Tennessee Valley Authority (TVA).

ACTION:

Issuance of Record of Decision.

SUMMARY:

This notice is provided in accordance with the Council on Environmental Quality's regulations (40 CFR parts 1500 to 1508) and TVA's procedures implementing the National Environmental Policy Act. TVA has decided to implement Alternative 2—Modify Dam and Maintain Summer Pool Level of 576 Feet, the preferred alternative identified in its Final Environmental Impact Statement (EIS), Bear Creek Dam Leakage Resolution Project.

FOR FURTHER INFORMATION CONTACT:

Charles P. Nicholson, NEPA Policy Program Manager, Environmental Stewardship and Policy, Tennessee Valley Authority, 400 West Summit Hill Drive, WT 11B, Knoxville, Tennessee 37902-1401; telephone [phone] or e-mail [e-mail].

SUPPLEMENTARY INFORMATION:

TVA completed Bear Creek Dam in 1969 at mile 74.6 on Bear Creek in Franklin County, Alabama. The dam and associated reservoir are part of the Bear Creek Project authorized for the purposes of flood control, recreation, and economic development, including water supply. Excessive leakage of water has occurred through the foundation of Bear Creek Dam since its completion and this increases the risk of dam failure. TVA has unsuccessfully attempted repairs on several occasions. The most recent of these repair efforts was in 2004-2005; after TVA refilled the reservoir to its normal summer pool level of 576 feet above sea level, excessive leakage continued. Since then, TVA has operated the reservoir at a reduced summer pool level of 568 feet as a precautionary measure to reduce the leakage and provide a greater margin for flood management. However, following periods of heavy rainfall, the reservoir level can rise, and the risk of dam failure increases. TVA prepared this EIS to evaluate alternatives for a long-term solution to the problem of excessive leakage through Bear Creek Dam.

TVA published a Notice of Intent to prepare this EIS in the Federal Register on June 2, 2006. A public scoping meeting was held on June 20, 2006 and attended by about 150 people. Scoping comments were received from two federal agencies, four state agencies, and several individuals. The Notice of Availability of the Draft EIS was published in the Federal Register on June 1, 2007. TVA held a public meeting on the Draft EIS on June 26, 2007 and accepted comments through July 16, 2007. Comments on the Draft EIS were received from three federal agencies, one state agency, three local public water suppliers, and three individuals. The Notice of Availability of the Final EIS was published in the Federal Register on August 10, 2007.

Alternatives Considered

TVA identified four alternatives in the EIS

Under Alternative 1, the No Action Alternative, TVA would not implement a long-term solution to the leakage problem and would attempt to operate the dam at the originally-intended summer pool level of 576 feet. Normal winter pool would remain at 565 feet. Under this alternative, TVA would implement new seasonal minimum flows from the dam as recommended by the U.S. Fish and Wildlife Service to improve habitat conditions for endangered species in Bear Creek downstream of the dam. Adoption of Alternative 1 would not remedy the leakage problem, and the dam would be at risk of failure, which would cause downstream flood damage. Although this alternative differs from the current interim operating regime, it better represents the historic baseline conditions.

Under Alternative 2, Modify Dam and Maintain Summer Pool Level of 576 Feet, TVA would repair or rebuild the dam in place or immediately downstream and restore the normal summer pool to 576 feet. TVA would also implement the new seasonal minimum flows described above for Alternative 1 and raise the normal winter pool by one foot to 566 feet. The existing roadway across the dam would be returned to service following dam repairs. Three sub-alternatives are considered under this alternative. Alternative 2a is the construction of a roller-compacted concrete structure at the downstream edge of the existing dam. This structure would be keyed into the bedrock, and a cutoff wall would be installed beneath the structure to prevent seepage. Alternative 2b is the placement of additional earth fill on the downstream dam face and the installation of a cutoff wall into bedrock on the downstream side of the dam. Alternative 2c is the installation of a cutoff wall into bedrock on the upstream dam face.

Under Alternative 3, Lower Dam and Maintain Summer Pool Level of 565 Feet, the existing dam would be partially removed and stabilized. A grout curtain or cutoff wall would be installed within the dam and into the underlying bedrock to prevent seepage under the dam. The existing roadway across the dam would be rebuilt. The reservoir pool level would be maintained at approximately 565 feet throughout the year.

Under Alternative 4, Remove Dam and Restore Former Creek Channel, TVA would remove Bear Creek Dam and the reservoir would be eliminated. The former creek channel would be dredged of excess sediment to facilitate water flow. A bridge would be built to replace the existing roadway over the dam.

Comments on the Final EIS

The U.S. Environmental Protection Agency (EPA) commented on the final EIS. Their comments focused on potential effects to wetlands and sought clarification of responses to previous EPA comments on the draft EIS. Due to favorable hydrologic conditions, approximately 77 acres of scrub-shrub, emergent, and aquatic bed wetlands have developed at various locations around the reservoir fringe at the interim summer pool elevation of 568 feet. None of these wetlands is forested. The forested wetlands on Bear Creek Reservoir are confined to the heads of coves where tributary streams enter the reservoir. The hydrology of these areas depends on the tributary streams, and the forested wetlands are generally unaffected by fluctuation in the reservoir level. Forested/scrub-shrub wetlands also occur on flats associated with Island Branch and further upstream. Based on the size of trees present, these wetlands have persisted in this location for over 20 years and would not be inundated when the reservoir is refilled. No forested wetlands would be affected adversely under Alternatives 1 and 2. Forested wetlands have not developed in the drawdown zone between elevation 576 feet (normal summer pool) and 565 (normal winter pool) because tree growth is inhibited by extended inundation during the growing season.

Because they perform only minor wetland functions due to their fringe nature and because traditionally accepted hydric soil characteristics are not present, TVA does not consider these wetlands to be jurisdictional wetlands in accordance with the Clean Water Act. Accordingly, no compensatory mitigation is required to offset their loss.

Bear Creek Reservoir is narrow with fairly steep, rocky banks and few areas of overbank. Fringe wetlands are likely to become reestablished along parts of the normal (576 foot) summer shoreline, particularly in bottomland areas associated with tributaries, if the reservoir were refilled under Alternative 1 or 2. Shoreline steepness and the presence of adequate soil substrate are the primary factors affecting wetland development at the current 568-foot summer pool level and at the 576-foot normal summer pool elevation under Alternatives 1 and 2. Competition from exotic plants or animal life does not appear to present any barrier to wetland establishment.

Much of the Bear Creek Reservoir shoreline has eroded since the reservoir was filled in 1969, and rock outcrops and bluffs are common along the shoreline. No critically eroding shoreline has been identified. At the 576-foot elevation, shoreline vegetation present prior to the 2005 emergency drawdown has not decreased. Refilling the reservoir under Alternatives 1 and 2 is not expected to cause additional erosion. Thus, establishment of shoreline buffers to prevent erosion is neither feasible nor necessary.

Returning the reservoir to its original full summer pool is expected to result in water quality conditions virtually identical to the pre-2005 conditions. Most of the shoreline surrounding Bear Creek Reservoir is undeveloped and forested. Runoff from upland areas enters the reservoir primarily via tributary streams. The degree of upland runoff filtered by wetlands is dependent on those wetlands present in coves and associated with streams. These areas have not been affected dramatically by changes in reservoir levels. Historically, low levels of dissolved oxygen have occurred in the deeper portions of the reservoir. Currently there are no plans to improve dissolved oxygen. However, TVA will continue to monitor water quality on Bear Creek Reservoir and would take remedial measures as necessary.

Decision

TVA has decided to implement Alternative 2, Modify Dam and Maintain Summer Pool Level of 576 Feet. Under this alternative, the original project objectives of flood control, recreation, economic development, and water supply would be met. The new seasonal minimum flows would improve conditions for endangered species downstream of the dam, and the one-foot increase in the winter pool level would improve operating conditions for the public water supply intake and treatment plant on the reservoir.

Three alternative methods of repairing the dam are identified in the EIS. TVA has selected Alternative 2a, the construction of a roller-compacted concrete structure at the downstream edge of the existing dam.

Environmentally Preferred Alternative

Alternative 2—Modify Dam and Maintain Summer Pool Level of 576 Feet is the environmentally preferred alternative. Implementation of this alternative would afford a stable water supply source for the Franklin County Water Service Authority and would restore water-based recreational opportunities on Bear Creek Reservoir. Repair of the dam under this alternative would provide increased flood protection to downstream areas compared to the other alternatives. Operation of the dam under Alternative 2 to provide target minimum flows would provide improved water quality for three federally listed mussel species known to occur downstream of Bear Creek Dam.

The potential environmental consequences of implementing any of the three Alternative 2 repair methods are similar. However, Alternative 2a—Roller-Compacted Concrete Structure is preferable to the other two methods in that it would most likely provide the best long-term solution to the leakage problems. It would provide protection against the probable maximum flood. The need for future construction disturbance would be reduced under Alternative 2a.

Mitigation

Standard construction best management practices would be followed in all aspects of the proposed repairs and construction to avoid or minimize adverse environmental impacts. TVA would ensure that all necessary permits are obtained from the appropriate regulatory agencies and that permit requirements are met. TVA would ensure that all site operations adhere to the requirements in each permit and would employ all necessary actions to minimize environmental impacts. The following non-routine measures would be implemented to reduce the potential for adverse environmental effects:

• Construction buffers would be delineated around any caves within one-fourth mile of a construction area. The buffer for caves would be 200 feet. Within this buffer, vegetation would not be cleared, and vehicles or equipment would be restricted to existing roads.
• TVA would increase patrols and monitoring of cultural resources within the reservoir drawdown area until conditions are stabilized or protected.
• Archaeological surveys as required by the Memorandum of Agreement between TVA and the Alabama State Historic Preservation Officer will be conducted, and mitigation will be performed on any sites or resources determined to be eligible for inclusion on the National Register of Historic Places in accordance with the terms of the Memorandum of Agreement.

Dated: September 10, 2007.

Janet C. Herrin,

Senior Vice President, River Operations.