Oral Presentation Society for Freshwater Science 2025 Annual Meeting

Characterizing the historic bentonite mining area near Belle Fourche, South Dakota, to develop an ecological restoration roadmap (117948)

Patrick Kozak 1 2 , Jennifer Walker 1 2 , Lisa Kunza 1 2
  1. Center for Sustainable Solutions, South Dakota School of Mines, Rapid City, SD, United States
  2. South Dakota School of Mines, Rapid City, SOUTH DAKOTA, United States

Abandoned minelands can exhibit environmental damage, especially where mining occurred before preventative environmental laws and regulations were enacted. Effective ecological restoration requires site-specific understanding of baseline conditions and barriers to ecological and hydrologic function. Surface mining of bentonite clays started in the early 1920s and continues today northwest of Belle Fourche, South Dakota. Our study focuses on approximately 8 square kilometers of these abandoned bentonite minelands, including over 3 square kilometers of public land managed by the United States Bureau of Land Management. The impermeability of the Belle Fourche Shale produces a landscape of water-holding mined locations. The EPA initially sampled eight ponds including associated soils for a Pre-Comprehensive Environmental Response, Compensation, and Liability Act (Pre-CERCLA) Screening following standard protocols. In 2024, we began site characterization using remotely sensed imagery to identify water bodies and to differentiate the landscape surface based on vegetation and soil brightness. The resulting strata included vegetated, dark, medium, and bright soils. At 18 sample locations distributed among these strata, we dug shallow soil pits and collected soil samples. We also identified 46 water locations where electrical conductivity, temperature, and pH were measured, and qualitative observations were recorded. Initial results showed conductivities for all water samples (43) but three were under 2,500 µS/cm, with the highest being 3,257 ± 69 µS/cm. This result was unexpected, as nearby rangeland impoundment conductivities show greater variability, ranging up to 15,000 µS/cm as the regional area has salinity issues in both soil and water. Qualitative observations of the waterbodies showed significant riparian development including biotic indicators. Soil analysis showed signs of soil development in undisturbed locations with established vegetation, but none in the other strata. Initial results suggest that facilitating ecological processes may provide a more productive pathway to restoration than attempting to reconstruct past reference conditions.