Controls on water quality below a reclaimed surface coal mine, southeastern Montana

Skye Keeshin; Stephanie A. Ewing; Elizabeth B Meredith; Robert A. Payne; W. Payton Gardner; Andrew Hunt

doi:10.1007/s10040-025-02898-z

Controls on water quality below a reclaimed surface coal mine, southeastern Montana

Hydrogeology Journal

By: Skye Keeshin, Stephanie A. Ewing, Elizabeth B Meredith, Robert A. Payne, W. Payton Gardner, and Andrew Hunt

https://doi.org/10.1007/s10040-025-02898-z

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Abstract

Coal mining and reclamation can have a profound influence on hydrogeologic systems, with clear consequences for groundwater quality, yet their long-term influence on downgradient water quality over time following reclamation is less well documented. Geochemical trends were evaluated in water quality downgradient of a fully reclaimed landscape at the former Big Sky Mine in the Rosebud Creek watershed (southeastern Montana, USA), over a 3-year period (2020–2022), including bond release in 2022. Within 6 km downgradient from the reclaimed area, sulfate concentrations decreased from approximately 3500 to 1800 mg l⁻¹ within the Miller Coulee alluvial aquifer. Major ions, δ³⁴S_SO4 values, and residence time tracers suggest that the observed decreases in sulfate concentration result from a combination of dilution by mixed-age inflows and incomplete transit of the high salinity plume from the mine boundary. Both bedrock and alluvial aquifers of the Rosebud Creek corridor contained contributions of millennia-old regional groundwater, which may serve to mitigate mine-derived high salinity waters. Rosebud Creek, which traverses the outflow zone of Miller Coulee in the study area, exhibited high sulfate concentrations during low flows and consistent downgradient increases in sulfate concentration. The possibility of plume dynamics in Miller Coulee suggests that the greatest water quality impacts may not yet have reached Rosebud Creek.

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Additional publication details
Publication type	Article
Publication Subtype	Journal Article
Title	Controls on water quality below a reclaimed surface coal mine, southeastern Montana
Series title	Hydrogeology Journal
DOI	10.1007/s10040-025-02898-z
Volume	33
Publication Date	May 14, 2025
Year Published	2025
Language	English
Publisher	Springer
Contributing office(s)	Geology, Geophysics, and Geochemistry Science Center
Description	23 p.
First page	715
Last page	737
Country	United States
State	Montana
Other Geospatial	Powder River basin