Pickwick Landing Dam South Embankment Seismic Upgrade

Update: 2019 Final Supplemental Environmental Assessment

In September 2016, TVA completed a final Environmental Assessment (EA) and Finding of No Significant Impact (FONSI) to document the potential effects of TVA's upgrades to the south embankment of Pickwick Landing Dam to improve performance of the dam during and following a large earthquake. These documents can be viewed below on this page below under "Related Documents".

Since the EA was completed, there have been changes to the design to reduce overall risks to the integrity of the dam during construction and to address construction challenges. On January 9, 2019, TVA issued a final supplemental environmental assessment and FONSI for the proposed changes to implement the necessary design changes to complete its upgrades at Pickwick Landing Dam. The proposed actions in the SEA resulting in additional area of impact include:

• Downstream Site Access Improvements: TVA is proposing to route construction vehicles to the work area via a newly constructed gravel access road that ties into North Carolina Landing Road at the driveway entrance. TVA is also proposing to close North Carolina Landing Road to public traffic at the intersection with State Highway 128 until the project is complete.

• Additional Downstream Footprint near Station (Sta.) 40+00: TVA is proposing to utilize a 0.89-acre low-lying area downstream of the dam as a stormwater sediment basin.

• Downstream Staging Area: TVA is proposing to utilize a grassed, gently sloping embankment area north of the downstream fill area as a staging area for fill stockpiles, construction materials, and construction equipment. This area also includes the area under the State Highway 128 bridge, which would connect the upstream and downstream work areas, reducing the need to use local roads to transfer materials and equipment between the two work areas.

• Barge Activities: At the time of the 2016 EA, it was anticipated that all fill materials would be delivered to the site by truck on local roads. TVA is now proposing an option for the contractor to build a temporary barge unloading site at the north end of the upstream dam work area, where fill materials can be shipped to the site via barge, unloaded at the barge unloading site on the dam, and transported under the State Highway 128 bridge structure to the downstream work zone. The proposed unloading site is in an area where upstream fill was already planned to be placed.  To support the use of the barge unloading site and the filling operation upstream of the dam, TVA is proposing to use two 35-acre upstream staging/fleeting areas. The areas would be used to temporarily store barges until they are needed at the fill placement work zone.

• Upstream Fill Area: TVA is proposing to increase the limits of the upstream fill approximately 0.47 acres to provide a safe design of the Upstream Fill Area.

• Upstream Site Access: TVA is proposing to close the access road to public traffic at the intersection with State Park Road. The dam crest would be fenced off and closed to the public during construction. The fencing would prevent access to this area of the dam, which is regularly used by the public for fishing.

• Downstream Fill South of Station 15+00: TVA is proposing to extend the downstream fill south of Sta. 15+00 to about Sta. 12+00 from 25.32 acres to approximately 28.06 acres to provide a safe design of the Downstream Fill South of Station 15+00.

TVA published a draft supplemental EA in October 2018 for public review and comment. TVA received a total of 3 comment letters; 2 from the State of Tennessee Department of Environment and Conservation and 1 from the National Park Service-Shiloh National Military Park.  TVA responded to these comments in the final supplemental EA.

Background

The EA and Finding of No Significant Impacts completed in September 2016 addressed TVA's proposed upgrades of the south embankment of Pickwick Landing Dam to improve performance of the dam during and following a large earthquake. A seismic stability evaluation of the embankment completed in 2014 indicates that a large earthquake could result in the loss of strength in some soil layers of the embankment, leading to slope instability and the breach of the dam. TVA informed the public of this potential and installed an early warning system in 2015 and began developing a proposal to strengthen the dam's embankment.

Upgrades would be made to both the upstream and downstream sides of the earthen embankment. Berms would be constructed along the toe of each side of the embankment and areas of extended fill would be placed in select locations. Under the proposal, a small area of TVA land along North Carolina Landing Road below the dam would be used for construction laydown activities. Activities would not close or restrict travel on Highway 128 crossing the dam. TVA does not propose to change its operation of the reservoir during construction (i.e., lake levels would continue to follow the existing seasonal patterns).  The upgrades to the embankment would allow TVA to avoid risk to public health and safety and the significant economic impacts that would result from having to lower the reservoir below winter pool levels for an extended period following an emergency.