Gaughan, T. | SRNS-J2000-2018-00131, 12 pp, 2018

The vadose zone and groundwater beneath the Old Coal Storage Area and the Coal Pile Runoff Basin at the Savannah River Site has been affected by low pH and dissolved metals over ~60 yr of power plant operation. The presence of a low-pH plume demonstrates that the buffering capacity of the sediments in the vadose zone and the aquifer has been overcome by sulfuric acid that has changed the charge of the soil from mostly negative to mostly positive such that dissolved metals present in the groundwater remain in solution. The coating of the sediment with hydrogen+ ion will allow the acid plume and impact on the discharge canal to persist for a very long time. Infiltrating water from the vadose zone and groundwater flowing into the acidic zone from upgradient will become strongly acidic when it comes into contact with the hydrogen+ ions in the sediments until most of the acidity is depleted. The sediments in D Area consist of relatively thinly interbedded sands, silts, and clays. The lack of massive clean sand strata does not support the injection of basic solutions to arrest the acid source term in the groundwater. The addition of alkaline earth metal solutions will tend to activate the clay bearing sediments near the site of injection, causing the clay to swell and likely reduce sediment permeability to a level where treatment is not possible. A more reliable method of treatment is to simply wash the hydrogen+ ion from the top of the water table with potable water and treat the acid conditions in the discharge canal. This paper offers a conceptual design of an injection well field and the expected effects on the water table surface. Acidic water treatment within the discharge canal can be provided by carbonate-reactive structures. It is likely that the in-field components of the remedy could be implemented for ~$600K. https://www.osti.gov/biblio/1423999-remediation-acidic-groundwater-impacting-discharge-canal-area