UPDATE ON THE F SEEPAGE BASIN FUNNEL AND GATE SYSTEM SITING AND PERFORMANCE, SAVANNAH RIVER SITE, AIKEN, SC

The Savannah River Site (SRS) occupies approximately 300 square miles of land adjacent to the Savannah River in South Carolina. SRS produced tritium, plutonium, and special nuclear materials for national defense and the space programs. The most contaminated stream on the SRS is Fourmile Branch, which discharges into the Savannah River.

The F Area Seepage Basin is the source of a large acidic contaminant plume in the groundwater that significantly impacts Fourmile Branch water quality. The plume contains radioactive and non-radioactive metals, and radioactive non-metals including tritium. The Irwinton Sand is the most permeable formation within the water table, and was likely deposited in a beachfront/tidal delta environment. This sand is underlain by the Twiggs Clay (called the “Tan Clay” on SRS), which acts as a leaky confining unit. The clay was probably deposited in a marsh/lagoon environment. The geometry, lithologic character, and thickness of the Irwinton Sand and the presence of the Twiggs Clay significantly effect contaminant migration within the plume.

SRS is using an innovative funnel and gate system to manage the release of tritium and metals (radioactive and non-radioactive) from the F Area Seepage Basins plume. The funnel directs water from the top of the aquifer, which is the least contaminated, through the gates where it is treated. The aquifer is treated with base within the gates which promotes the precipitation of metals. The migration of untreatable contaminants (tritium and anions) is reduced by managing the aquifer water balance at the top of the aquifer.

The system has been in operation for approximately 5.5 years. Since installation the flux of tritium to Fourmile Branch from the F Seepage Basin plume has dropped by ~70%. A barrier extension is being constructed and will provide greater reductions. Future plans include field deployment of an Iodine-129 capture system using colloidal silver compounds.