Risk-based management strategies and innovative remedies for surface water protection: A case study

Releases of chlorinated aliphatic hydrocarbons have impacted soils and groundwater at a South Carolina facility. Plume discharges into nearby tributaries have contaminated surface waters with up to 4,600 mug/L of trichloroethene. Hydrogeologic studies, flow modeling, and pilot tests were performed to develop surface water protection remedies. Part of the groundwater plume migrates off-site to the northeast and discharges into an underground storm water pipe and into a pond. Studies found that >99 percent of chlorinated hydrocarbons in the pond and downstream tributary originate from infiltration of contaminated groundwater into piping upstream of the pond. A surface water protection plan was developed using risk-based, innovative treatment approaches. The plan proposed plume containment by the subsurface pipe and in-situ treatment of water in the pipe. Risk-based components of this remedy included fencing the pond and developing wildlife - and human health-based standards for the pond and its downstream tributary. Successful pilot testing was conducted using air diffusion and ozone oxidation for water treatment inside the pipe. Remedies for off-site surface waters west and south of the facility utilize in-situ enhanced reductive dechlorination treatment barriers around the tributaries. Trichloroethene was reduced in surface water and in the aquifer by 43%-99% in these areas.