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Supplemental Environmental Assessment

Russellville Water Intake

Addition of special reservoir drawdown during construction of intake at mile 32.4R on Cedar Creek Reservoir, Franklin County, Alabama

Proposed decision and need
Background
Other environmental reviews and documentation
Alternatives and comparison
Evaluation of impacts of reservoir drawdown
Cumulative effects
Mitigation measures
Preferred alternative
TVA preparers

Proposed decision and need

The Water Works and Sewer Board of the City of Russellville, Alabama plans to begin construction of a raw water intake structure on TVA Tract Number XTBCCER-1PS after October 1, 2003. In July 2001, the U.S. Army Corps of Engineers (USACE) prepared an environmental assessment (EA) for the impacts of Section 10 actions related to construction of a water intake. On August 27, 2001, TVA adopted the EA and issued a Finding of No Significant Impact (FONSI) for its actions related to the project. These approvals would allow Russellville to construct a raw water intake with a withdrawal rate of six million gallons per day on Cedar Creek Reservoir, a pumping station on TVA land, and a six mile pipeline between TVA’s Cedar Creek Reservoir and Russellville’s water supply reservoir (Lake Elliot).

Recently, the City has requested that TVA provide a special water level of elevation 550 feet at mean sea level (MSL) for a 14-day period to allow the contractors to excavate and construct the concrete channel for the intake structure. This level is 30 feet below normal summer pool of 580 msl and 16 feet below minimum winter pool of 566 msl.

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Background

The water intake was previously approved under Section 26a of the TVA Act and permanent easements were granted over 2.86 acres of TVA land for the associated water pipeline. The water intake is requested because of recent droughts which have stressed the ability of the City of Russellville to meet its drinking water needs. The City’s existing water supply reservoir, Lake Elliot, located on Dunkin Creek upstream from Cedar Creek Reservoir, does not store enough water during dry periods. The water withdrawn would be pumped to the City’s existing water treatment plant on Lake Elliot.

Other environmental reviews and documentation

TVA Finding of No Significant Impact and Adoption of U.S. Army Corps of Engineers Environmental Assessment – Russellville Water Works Board – Section 26a Approval for Water Intake at Mile 32.4R, Cedar Creek and Permanent Easements for Water Pipeline Affecting 1.02 Acres of Tract No. XBCCER-34PT, 1.19 Acres in Two Locations on Tract No. XBCCER-33PT, and 0.65 Acres on Tract No. XBCCER-31PT.

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Alternatives and comparison

The EA prepared by the USACE evaluates the environmental consequences of three alternatives, No Action, the Applicant’s Proposed Action, and the Applicant’s Proposed Action with Special Conditions. The alternative selected by both agencies was the Applicant’s Proposed Action with Special Conditions. This supplemental EA evaluates the City of Russellville’s additional request that TVA provide a 14-day water level of 550.00 elevation to allow the contractors to excavate and construct the concrete channel for the intake structure.

The No Action Alternative. For this supplemental EA, the No Action Alternative is the Applicant’s Proposed Action with Special Conditions as described in the Final Environmental Assessment. The water intake, pumping station, and pipeline would still be constructed. During construction of the water intake, the applicant would be required to use a floating turbidity curtain to surround the proposed excavation site in the reservoir. The applicant would be required to construct cofferdams or equivalent best engineering practices to dewater the area in the location of the proposed pumping station to minimize sedimentation and turbidity levels. The applicant would also have to use precast concrete in order to avoid wet cement contact with the reservoir. The potential impacts associated with this alternative were evaluated in the EA (see Other Environmental Reviews and Documentation).

Reservoir Drawdown Alternative. Under this alternative, TVA would lower the reservoir elevation to 550 msl. This would create a dry area around the bottom elevation of the water intake structure, which is 555 msl. Wet concrete could be poured in the dry, and appropriate stormwater controls would be used around the construction area. As a result, construction impacts and costs to the City of Russellville would potentially be reduced. Under this alternative, the Applicant would still be required to utilize the special conditions as described in the EA where applicable.

Compared to the No Action Alternative, the construction would be conducted in the dry, eliminating the need for special conditions for dewatering the construction area, the need for turbidity curtains and/or cofferdams, and the placement of wet cement in the reservoir. Also, dewatering operations and the use of precast concrete and turbidity curtains would increase construction time and costs. Therefore, the special drawdown would be environmentally superior to the No Action Alternative. Other impacts of the Reservoir Drawdown Alternative, including construction of a pump station and water transmission line between Cedar Creek Reservoir and Lake Elliot, would be the same as under the No Action Alternative and were evaluated in the EA.

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Evaluation of impacts of reservoir drawdown

Resources potentially affected by the Reservoir Drawdown Alternative are recreation, water quality, aquatic life, and cultural resources. Because the drawdown would occur during the fall when recreational use is low, effects from the special drawdown on public recreation resources, facilities, and activities are expected to be temporary and insignificant. As part of the communications process for special drawdowns, TVA would notify the recreating public prior to this change in Reservoir Operations.

Potential impacts to aquatic life and water quality would be through increased sedimentation during the drawdown, dehydration of benthic organisms, fish entrapment and sedimentation, and streambank erosion below the dam. Since Cedar Reservoir usually has a large drawdown each fall, the larger drawdown zone would not lead to significantly greater amounts of sediment run-off from this area. No significant loss of benthic life would be expected in the added drawdown zone because of poor dissolved oxygen levels during summer months. The pre-impoundment topography of the reservoir shows no depressions or sink-holes that could contribute to fish entrapment. Similar releases from Cedar Reservoir Dam occur each year during normal drawdown operations; therefore, no streambank erosion from this action is expected below the dam.

Archaeological resources are known to be present below the normal pool of Cedar Creek Reservoir. However, the proposed temporary drawdown does not have the potential to affect these resources. The only potential impact on cultural resources from the lower drawdown would be in opportunistic looting of identifiable exposed archaeological sites. Periodic patrols by the TVA Police during the 14 day drawdown would limit the risk of looting.

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Cumulative effects

There are no other current proposed actions or reasonably foreseeable future actions on Cedar Creek Reservoir which would cumulatively affect the resources affected by the Reservoir Drawdown Alternative.

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Mitigation measures

The following special conditions previously identified in the August 27, 2001, TVA FONSI are still needed and consequently would also be a requirement of the revised TVA approval. Commitments number 6 and 7 would still be needed in the event that the drawdown could not be maintained during construction. In addition, TVA would commit to increasing TVA Police patrols as discussed above.

1. Water withdrawn from the proposed water intake shall not be transferred from the Tennessee River Basin to another river basin without prior approval of TVA.

2. The applicant will comply with all 18 conditions listed in the March 19, 2001 Section 401 Water Quality Certification issued by the Alabama Department of Environmental Management.

3. The proposed waterline must not provide connections for facilities that support development within the limits of the 100-year floodplain of streams within the water service area.

4. All items and equipment subject to flood damage on Cedar Creek Reservoir will be located above or floodproofed to the 100-year flood elevations 589.0.

5. All activities associated with construction, excavation and backfilling will occur during the dry season.

6. A floating turbidity curtain will be placed in the reservoir in an area surrounding the proposed excavation site.

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7. The area in the location of the proposed pumping station will be dewatered. Wet cement contact with the reservoir will be avoided.

8. All excavated material, including rock materials used for the temporary cofferdam (if constructed) shall be disposed of properly and removed from the site above the 100-year floodplain elevation.

9. The intake structure shall possess a screen or other mesh-like apparatus that would allow water to flow into the pipe but would prohibit or prevent fish and other aquatic species to become entrained in the structure.

10. Best Management Practices and Best Engineering Practices will be used throughout the life of the project to prevent the introduction of soil or any other pollutants into the reservoir, including immediate revegetation or other stabilization of disturbed onshore areas. This includes TVA standard BMPs 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, and 6i.

11. Any rock or riprap that covers trenches will be placed in a way that would not impede future stream flow or impede the migration of aquatic species. Elevation of the top of the riprap shall be no higher than the elevation of the existing streambed.

12. To prevent opportunistic looting of exposed archaeological sites, TVA Police will patrol the reservoir periodically during the 14 day drawdown, provided the national security level does not limit TVA Police’s resources in the area.

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Preferred alternative

Because of reduced environmental impacts and ease of construction, TVA’s Preferred Alternative is the Reservoir Drawdown Alternative.

TVA preparers

J. Bennett Graham, Senior Archeologist, Norris, Tennessee
Richard Pflueger, Land Use Specialist (Recreation), Muscle Shoals, Alabama
Helen G. Rucker, Senior NEPA Specialist, Knoxville, Tennessee
Damien Simbeck, Watershed Specialist, Muscle Shoals, Alabama

 

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