Conceptual Groundwater Remedial Alternatives at Coal Combustion Residuals Sites†

Groundwater below many basins that have been used to store coal combustion residuals (CCRs) may have concentrations of certain inorganic constituents in excess of applicable regulatory standards. Given that many inorganic CCR constituents are also naturally occurring in the aquifer matrix, their detection may not always be indicative of a release from the CCR unit. Inorganics may be present at elevated levels in groundwater due to natural or background conditions, or due to changes to the aquifer geochemistry resulting from the presence of the CCR basin, which then mobilizes these naturally occurring constituents beneath the CCR unit. Care must be taken to identify the source(s) and the release mechanism(s) of potential CCRrelated impacts. If a link between a CCR unit and an inorganic groundwater exceedance has been established, stakeholders may be faced with the need to evaluate groundwater remedial alternatives to address these impacts. This paper conceptually discusses potentially applicable remedial approaches, including (i) monitored natural attenuation, (ii) hydraulic control using ex situ and in situ methods, (iii) permeable reactive barriers, (iv) slurry walls, and (v) oxidation-reduction–altering approaches. Additionally, this article explores potential water reuse options available at many power generating stations.