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