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COMPARING ROCK MATRIX CONTAMINANT PROFILES DOWNGRADIENT OF A DNAPL SOURCE AFTER 10 YEARS OF GROUNDWATER DISSOLUTION
Buckley, A., J. Meyer, D. Austin-Blaine, and B. Parker.
Abstracts: NGWA Conference on Fractured Rock and Groundwater, Burlington, VT, 2-3 October 2017

Prior to 1970, over 70,000 L of DNAPLs were released into the subsurface at a site in south central Wisconsin. The mixed organic DNAPL migrated through unconsolidated glacial sediments and shallow sedimentary bedrock, eventually accumulating ~56 m bgs in fractured sandstone. A study was conducted to characterize the temporal evolution of contaminant mass in the source zone by comparing two co-located rock core VOC concentration profiles, one collected in 2003 and the other in 2014. The rock core VOC profiles provided depth-discrete and detailed (at least 1 sample/ft of core) quantification of the contaminant mass in the rock matrix. The 2003 core showed relatively uniform rates of mass accumulation with depth for most contaminants, whereas the 2014 core showed highly variable rates of mass accumulation with depth, particularly in the shallow rock units. These results indicated variable attenuation rates for specific depth horizons. Assessment of specific contaminants showed declines in concentration for parent ethanes and ethanes, dichloromethane, and MIBK and increases in concentrations for daughter products (e.g., chloroethane, VC). Core and borehole geophysical logs and hydraulic testing provided site-specific parameters for evaluating the influence of various attenuation processes (e.g., dispersion, diffusion, sorption, abiotic/biotic degradation) on source zone fluxes and longevity. See more on this project in A. Buckley's thesis at http://atrium.lib.uoguelph.ca/xmlui/handle/10214/10464.



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