Groundwater remediation in fractured rock: challenges to solutions

Pollution derived from human activities has entered consolidated igneous, sedimentary, or metamorphic rock formations that store valuable groundwater resources or are in physical proximity to these resources. Many of these formations are distinguished by complex patterns of discontinuities (generally "fractures") that break up the physical continuity of the crystalline or granular rock matrix. The spatial relationship of fractures to the matrix can be extremely important in influencing pollutant or contaminant persistence and migration through the subsurface, the associated threat or risk, and how the threat or risk might be ameliorated through active treatment or remediation. Different remediation approaches have been applied to groundwater-saturated fractured rock including technologies for contaminant extraction, containment, and in-situ treatment. Pilot and full-scale remedial actions have historical focused for the most part on preventing contaminant plume spread via hydraulic containment or demonstrating through monitored natural attenuation (MNA) that risks can be managed without active treatment. Numerous in-situ pilot tests and some full-scale actions have been pursued but there are few published examples and even fewer that document successful outcomes, such as meeting maximum permissible contaminant levels for drinking water, after completion of at least a few years of performance assessment monitoring. (author)