Surface coal mining has altered Appalachian landscapes, affecting water quality and aquatic ecology. Valley fills created from excess overburden are prominent features of many mined landscapes. Increased total dissolved solids (TDS), as measured by its surrogate specific conductance (SC), is a significant water quality concern related to the exposure of fresh mineral surfaces to weathering in valley fills. Specific conductance levels in waters draining Appalachian mined areas are highly variable, yet the causes for this variability are not well known. Here we sought to improve understanding of such variability by investigating the interior subsurface structure and hydrologic flowpaths within a series of valley fills and relating that to valley fill characteristics such as age and construction method. We used electrical resistivity imaging (ERI) to investigate the subsurface structure of four valley fills in two dimensions. We combined ERI with artificial rainfall to investigate the location and transit time of hydrologic preferential infiltration flowpaths through the fills. Finally, we used our ERI results in conjunction with SC data from effluent streams to improve understanding of SC relationship to fill flowpaths and characteristics. ERI results indicated considerable variability in substrate type and widespread presence of preferential infiltration flowpaths among the valley fills studied. We estimated an average preferential flowpath length of 6.6 meters, average transit time of 1.4 hours, and average velocity of 5.1 m/h or 0.14 cm/s through preferential infiltration flowpaths. ERI successfully distinguished fills constructed using methods of conventional loose-dump and experimental controlled-material compacted-lift construction. Conventional fills had greater ranges of subsurface resistivity, indicating a wider range of substrate types and/or more variable moisture content. Conventional fills also showed more accumulation of water within the fill during artificial rainfall, possibly indicating more quick/deep preferential infiltration flowpaths than in the experimental fill. Relationships between other fill characteristics as well as stream effluent SC were not related in a statistically significant way to fill structure or flowpaths. ERI appears to be a robust non-invasive technique that provides reliable information on valley fill structure and hydrology, and experimental compacted-lift valley fill construction produces significantly altered hydrologic response, which in turn affects downstream SC. / MS / Surface coal mining has altered Appalachian landscapes, affecting water quality and aquatic ecology. Valley fills created from excess mine spoil are prominent features of many mined landscapes. The streams draining valley fills often have very poor water quality, including high levels of increased total dissolved solids (TDS) related to weathering of mine spoils within valley fills. In this work, we investigated the subsurface structure of a series of valley fills and identified preferential hydrologic flowpaths, which are the “paths of least resistance” water follows for rapid infiltration. We related our results to various valley fill characteristics such as age and construction method. We found that the subsurface of a conventionally built fill tends to have more variation in material and/or moisture content than a fill built with an experimental construction method. Conventional fills also showed more accumulation of water within the fill during artificial rainfall experiments, possibly indicating more quick/deep preferential infiltration flowpaths than in the experimental fill.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/94131 |
| Date | 04 April 2018 |
| Creators | Little, Kathryn Leigh |
| Contributors | Environmental Science and Engineering, Hester, Erich T., Burbey, Thomas J., Widdowson, Mark A., Zipper, Carl E. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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