Evaluation of High Resolution Methods for Contaminant and Flux Distributions in Igneous / Metamorphic Rock Settings
Tuesday, September 24, 2019: 10:30 a.m.
Characterization of contamination in fractured bedrock is a pervasive and challenging problem. While nearly all groundwater flow occurs in the fracture network, diffusion transfers mass to the matrix causing attenuation of downgradient transport, but also acting as an impediment to plume cleanup. High resolution rock core sampling using efficient and robust methods for sample collection, processing and lab extraction and analysis has been shown to be effective at many sedimentary bedrock (e.g. sandstone, mudstone) and a few crystalline bedrock sites for assessing contaminant distributions, while minimizing cross-connection effects that can confound assessment of groundwater concentrations. However in low matrix porosity igneous / metamorphic bedrock (e.g. granite, gneiss) with negligible matrix sorption, rock core sampling techniques are more challenging and may not always be diagnostic. This presentation will focus on insights from multi-method high resolution characterization at a chlorinated solvent contaminated site in Sweden involving rock core sampling, FLUTe FACT™ and depth-discrete groundwater sampling, along with complementary profiles from geophysical and hydrophysical logging. These datasets provide unique insights regarding method performance and biases (drilling disturbance, cross-connection and method sensitivity) for crystalline rock in contrast to sedimentary rock systems, and ultimately inform conceptual site models for transport to improve remediation decisions.