The Tennessee Valley Authority has released a draft of its environmental assessment of the planned Boone Dam repair project.
This draft, which will be available for public comment until Nov. 30, details the decision-making processes TVA used to develop a proposed repair for Boone Dam and examines the potential environmental impacts of the current proposal and the other alternatives TVA considered.
The EA reviews the potential environmental effects of the construction activities proposed to remediate seepage at Boone Dam, as well as the associated drawdown of the reservoir. This environmental review is necessary to comply with the National Environmental Policy Act and can help TVA identify, avoid and mitigate potential environmental effects, the agency says.
TVA proposes 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 would consist of an injected grout curtain and an excavated and filled concrete diaphragm wall. The remediation could take five to seven years and cost $200 million to $300 million.
Seepage under the embankment was discovered in October 2014, in the form of a sinkhole at the base of the structure. The sinkhole was repaired but a few days later seepage was discovered near the location of the original sinkhole. A thorough investigation revealed a complex series of underground geological pathways allowing water from both upstream and downstream sources to cause internal erosion. If left uncorrected, the erosion could eventually lead to failure of the dam.
Boone Dam impounds water for an 89-MW hydroelectric powerhouse.