Boone Dam Seepage Remediation
Sullivan and Washington Counties, Tennessee
Update: 2020 Final Supplemental Environmental Assessment
In January 2016, TVA issued a final Environmental Assessment (EA) and Finding of No Significant Impact (FONSI) for the construction activities to remediate seepage at Boone Dam, as well as the associated drawdown of the reservoir water levels. The environmental review of the proposed fix to the dam, located on the border between Sullivan and Washington Counties, Tennessee, helped TVA identify, avoid and mitigate potential environmental effects of the proposed project.
The EA analyzed the effects of our proposal to fix the dam by building a composite seepage barrier from the crest of the dam’s earthen embankment into the foundation soils and bedrock. The barrier proposed by TVA would consist of an injected grout curtain and an excavated and filled concrete diaphragm wall. In addition, TVA would use lands managed by us near the dam for construction support activities and would continue the reservoir drawdown through construction. The EA also addressed how TVA would manage successional vegetation growing in the drawdown area. TVA estimated that the remediation could take up to seven years.
After the EA was completed, TVA identified several minor changes to how the final stages of the project would be implemented. In February 2019, TVA issued a final supplemental EA and FONSI to review:
- The restoration of the dam’s earthen embankment after completion of the seepage barrier: TVA proposes to erect a floodwall on the dam’s crest.
- The disposal of construction spoils generated during the cutoff wall construction: TVA proposes to truck the spoils to nearby disposal facilities.
- The use of nearby lands for construction support activities: TVA would not use the Earl Light Tract for permanent placement of construction spoils, thereby reducing the majority of impacts to the land. Closing a portion of Minga Road would not be necessary and the tract would be reopened for public use earlier than anticipated.
The 2019 supplemental EA also provides additional information about how TVA would manage wastewater and stormwater during construction of the cutoff wall.
On June 11, 2020, TVA issued a second supplemental EA and FONSI that addresses the use of herbicides to manage vegetation growing in portions of the reservoir drawdown area. During 2019, TVA found that its mechanical treatments of vegetation were inadequate to treat some areas within the exposed reservoir bottom that are difficult to access (e.g., areas with steep slopes, rock outcrops, or bluffs) or where there are sensitive natural or cultural resources. To supplement its vegetation management plan, TVA reviewed the use of an herbicide mixture to kill or inhibit growth of vegetation in approximately 600 acres of reservoir bottom. TVA would apply formulations of the herbicides Imazapyr and Triclopyr, which have been approved by the Environmental Protect Agency for use within aquatic and riparian settings. A surfactant and marker dye would also be included in the mixture.
TVA plans to have a contractor spray these areas during summer 2020, beginning in June. Herbicides would be applied in accordance with the manufacturers’ label directions, and numerous best management practices and mitigation measures would be implemented. TVA would notify affected landowners of these activities. TVA would also continue working with the Tennessee Wildlife Resources Agency to address the potential hazards to boaters from vegetation in the reservoir once water levels are raised.
In October 2014, a sinkhole was discovered near the base of the embankment at Boone Dam, and water and sediment was found seeping from the riverbank below. TVA began assessing the dam’s condition and developing a remediation plan. In October 2015, TVA released a draft EA assessing the environmental impacts of the remediation plan. The draft EA was made available for public review and TVA hosted a public meeting in Johnson City to present its findings and solicit input. TVA considered all comments that were received during the review period. These comments and TVA’s responses are included in an appendix to the final 2016 EA.
TVA also completed a review of how the project complies with the White House Council on Environmental Quality’s policy established in Principles and Requirements for Federal Investments in Water Resources (March 2013). TVA conducted a review of the principles, requirements, and guidelines for water resources investments (PR&G Review) consistent with the Federal Interagency Guidelines issued in June 2015.
More information on this environmental review can be obtained from:
The Boone Dam Project
TVA has found the fix for seepage at Boone Dam: a composite barrier made of non-erodible material. Construction will take five to seven years. Maximum safety measures for area residents and businesses will remain in place throughout the process. Find out more about what happened at Boone Dam, why and how a team of the country’s finest dam engineers and safety experts arrived at the best possible solution. Read more about the Boone Dam Project.