Evaluating Methods to Protect the Columbia, SC Wastewater Treatment Plant
The City of Columbia, South Carolina’s Metro Wastewater Treatment Plant (WWTP) is located immediately at the land side toe of the Congaree River levee. Built in the 1960s and 70s, the levee is classified as non-accredited for the National Flood Insurance Program (NFIP). In October 2015, historic rainfall led to widespread flooding in the region and a section of the levee just downstream of the WWTP breached. Since the WWTP is higher in elevation than surrounding areas, it did not flood, but it was inaccessible to vehicular traffic for more than three days, employees had to be transported to and from the facility by boat, and the plant could not receive supplies.
The City of Columbia was awarded a grant by the Federal Emergency Management Agency (FEMA), which they used to retain Weston & Sampson as their prime consultant to conduct a geotechnical, climate resiliency, and flood protection study to evaluate alternative methods to protect the plant, its planned expansion, and its supply route from future flood conditions. Our study involves inspection of the existing levee, regional hydraulic and hydrologic analyses, breach analyses, subsurface explorations, and stability and seepage analyses for the existing levee in future flood conditions. Due to the high flood levels expected for the area, our recommendations include a new ring levee around the WWTP, raising the existing supply route to the facility, and building a new bridge off the highway as a secondary supply route.
When our study is complete, the City will have a series of solid, science-based recommendations for next steps to be undertaken to help protect this currently vulnerable infrastructure from flooding. Our recommendations will be critical in building resiliency into the plant and levee to better withstand threats from flooding from today’s as well as future storm events that are predicted to be more frequent and more severe due to climate change. Our study will include proposed additional studies and projects, as well as a path to getting the existing levee section to be accredited by the NFIP.