Geochemical and isotopic assessment of regional groundwater flow and aquifer connectivity in the Lisbon Valley, Utah

Chandler E. Noyes, Mark Person1, Grant Ferguson2, Jihyun Kim, and Jennifer McIntosh

Hydrology and Atmospheric Sciences
The University of Arizona

Understanding aquifer connectivity is an important water resource management practice to mitigate migration of contaminants from a mined aquifer (e.g. in-situ copper mining) to adjacent aquifers.  This study focuses on the metal-rich Lisbon Valley of the Paradox Basin in southeastern Utah where numerous faults may act as conduits or barriers to cross-formational flow.  All geochemical and isotopic results show that these distinct aquifers are hydrologically isolated.  The upper Burro Canyon (BC) aquifer has a calcium-sulfate signature with high TDS, while the lower Navajo (N) aquifer has a sodium-bicarbonate water with low-to-moderate TDS.  Corrected radiocarbon ages in the BC-aquifer of 3,000-11,000 BP coupled with higher δ18O and δD values are indicative of Holocene recharge.  Corrected radiocarbon ages in the N-aquifer of 15,000-38,000 BP coupled with lower δ18O and δD values are indicative of Late Pleistocene recharge, likely from the La Sal mountains based on regional hydraulic head gradients.  Near-zero to negative values of δ34S-SO4 and δ18O-SO4 in the BC-aquifer are consistent with sulfide oxidation in the mineralized aquifer, while positive values of δ34S-SO4 and δ18O-SO4 and lower [SO4] in the N-aquifer are indicative of bacterial sulfate reduction.  Groundwater in the N-aquifer is generally more radiogenic (higher 87Sr/86Sr) than in the BC-aquifer.

1New Mexico Institute of Mining and Technology, Department of Earth and Environmental Sciences, Socorro, NM 
2Department of Civil and Geological Engineering, University of Saskatchewan, Saskatoon, Canada

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