Date
Tuesday, September 10, 2024
Time
4:15 PM - 4:45 PM
Location Name
M104
Name
Shaking it Up – A Dam Seismic Retrofit Forces Change to Raw Water Intake
Track
Clean Water Technology
Description

A recent seismic update at Lake Pickwick Dam near Savannah, TN forced the Tennessee Valley Authority (TVA) to help First Utility District of Hardin County (FUDHC) relocate and update their raw water intake (RWI). The seismic renovation included widening the girth of the dam with 100 million tons of limestone to comply with the Department of Homeland Security dam regulations post September 11th attacks. Since the FUDHC’s RWI screen and pipeline lay in the path of this upgrade, FUDHC was forced to relocate it. This project was heavily scrutinized by the Tennessee Department of Environment and Conservation (TDEC), TVA Environmental Division, and ultimately the Army Corps of Engineers (USACE). Red tape and barriers were slowly broken down and the project was approved after 2 years of review and deliberation. Permits required included a USACE Joint Application 404 Permit, TDEC Aquatic Resource Alteration Permit, and a series of environmental permits from the TVA. The project was ultimately funded to address critical concerns that had limited the utility district for multiple decades. Design for the project included the layout and resizing the intake pipe and screen system. Hydraulic calculations verified that the existing intake pipe and screen were limiting the capacity of the 4 million-gallon a day (MGD) pump station. With a larger intake pipe and screen, FUDHC could meet the design capacity of the recently expanded water plant. The intake pipe was sized and extended an additional 150 feet into the lake to decrease the high levels of organics being sucked into the plant. The RWI was also equipped with an upsized air burst system and pigging port to accommodate cleaning efforts of sedimentation. Design efforts were completed, bids were received, and the project was awarded while construction difficulties were looming on the horizon. Construction in Lake Pickwick was subaqueous and stretched the contractor excavating through decades of silt layers and hidden boulders that had to be removed for pipe installation. Geotechnical subsurface investigation showed a very fine silt layer followed by clay and ultimately bedrock. Massive rocks encountered during foundation pile installation frustrated the plan and led to a pivot in bedding for the new intake. While it was clear that a change was imminent, the environmental permits clearly prohibited the import of foreign materials to the site. This left the contractor and the dive teams at a stand still waiting on a variance request for imported gravel to be added to the lake. Imported material was approved to avoid costly alternatives of sifting the silty material and the buried portion of the pipe was ultimately approved for installation using underwater open cut methods. The project was a success and valuable lessons were learned from the process. This presentation will address the unique obstacles from permitting with TVA to unique construction hurdles. The design and construction of the project provided ample areas of difficulty that had to be reconciled and will benefit our industry’s technical leaders avoid pitfalls for future endeavors.