Date of Award

6-2014

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor(s)

Donald I. Siegel

Keywords

Contamination, Geochemistry, Groundwater, Landfill, Modeling, Wyoming

Abstract

The Wyoming Department of Environmental Quality (WDEQ) suggested landfills across the State are contaminating groundwater with landfill leachate, soliciting an investigation of what useful aquifers might be contaminated, and whether remediation could be appropriate. My research goal is to broadly characterize groundwaters statewide to analyze the validity of WDEQ contamination claims, discuss the reliability of the WDEQ determination, and provide a feasible model of natural groundwater conditions. Volatile anthropogenic compounds such as acetone, methyl chloride, and dichlorobenzene are present in landfill leachte in discarded solvents and clearly can be used to characterize landfill leachate contamination. However, the WDEQ also uses concentrations of inorganic solutes, such as bicarbonate, sulfate, and chloride to fingerprint landfill contamination of groundwater. I explored an extensive chemical database on groundwater quality around landfills across Wyoming and found that typical solute concentrations of sodium, sulfate, and chloride the State uses to indicate contamination do not significantly correlate with volatile anthropogenic organics in contaminated water samples, such as benzene and toluene. Furthermore, correlations between major ions in the WDEQ dataset reflect naturally poor water quality where concentrations of chloride, iron, magnesium, sodium and sulfate exceed regulatory standards because of natural processes including ion exchange and evaporation. In addition, concentrations of the minor solutes iron and manganese commonly exceeded thermodynamic constraints by orders of magnitude because particulate material in samples was not removed prior to analysis. To determine how poor water quality naturally evolves in Wyoming basin fill and to determine the extent to which sampled water beneath landfills may be recently recharged I focused on the Sand Draw landfill, for which filtered hydrologic and geochemical data were available. Carbon isotopes of dissolved organic carbon and water isotopic data collected at the Sand Draw landfill indicate that water under this landfill occurs not in a regional water table but in perched water zones so isolated from modern recharge that the water is thousands of years old. I used Netpath, an interactive code for modeling net geochemical reactions developed by the USGS, to develop a feasible geochemical model representing the source of naturally poor water quality in the absence of landfill leachate contamination at the Sand Draw landfill. These heuristic simulations indicate ion exchange coupled to carbonate dissolution lead to poor drinking water quality in the basins of Wyoming.

Access

Open Access

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