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Case Studies |
1 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6400, USA
4 Department of Geological Sciences, University of Tennessee, Knoxville, TN 37996, USA
2 Department of Earth and Atmospheric Sciences, St Louis University, St Louis, MO 63103, USA
3 Geological Survey of Canada, Mineral Resources Division, Ottawa, Ont. K1A 0E8, Canada
Thirty-eight mudrock samples from the Cambrian Conasauga Group were analysed by immersion, helium and mercury porosimetry. The data generated from these techniques include effective porosities, pore throat size distributions and sample densities. The purpose of these analyses was to obtain information required to evaluate the capacity of the Conasauga Group mudrock to retard transport of and to store contaminants on the Oak Ridge Reservation (East Tennessee, USA). Results indicate that the three porosities were 9.90±2.61%, 3.8±0.7% and 8.1±4.3% for immersion (
I), mercury (Hg) and helium porosity (he), respectively. These values are considerably higher than those previously reported for these rocks (0.1–3.4%). The Hg values are commonly the smallest of the three. Although the three porosities generally show little change with depth, an expected trend as a result of the maximum burial depth of the Conasauga Group of >4 km, a decrease with depth is seen in some of the coreholes for only I. Furthermore, inconsistencies between the different porosity types provide an insight into the mudrock pore structure and related geochemical characteristics. For example, they indicate the existence of considerable pore space accessed only through <3 nm pore throats and the possibility of meteoric cement having replaced original diagenetic cement for some mudrock samples, which would lead to a possible instability to immersion with contaminated water. These characteristics have significant implications for the evaluation of the mudrock retardation and storage capacity for contaminants, and the design of remediation measures.
