Arden D. Davis

Water quality impacts from mining in the Black Hills, South Dakota, USA

The focus of this research was to determine if abandoned mines constitute a major environmental hazard in the Black Hills. Many abandoned gold mines in the Black Hills contribute acid and heavy metals to streams. In some areas of sulfide mineralization local impacts are severe, but in most areas the impacts are small because most ore deposits consist of small quartz veins with few sulfides. Pegmatite mines appear to have negligible effects on water due to the insoluble nature of pegmatite minerals. Uranium mines in the southern Black Hills contribute some radioactivity to surface water, but the impact is limited because of the dry climate and lack of runoff in that area.

An Educational and Research Well Field

Since 1982 an operational well field consisting of a main well and 14 observation wells has served as an educational and research facility for students at South Dakota School of Mines and Technology. An alluvial aquifer 1.5 m thick is located at shallow depths near the Mineral Industries Building. Student projects include measurement of the static level, preparation of maps of the potentiometric surface, pumping, slug, and tracer tests, and flow and transport modeling. Drawdown during pumping tests follows the Theis nonequilibrium-type curve with transmissivity averaging 390 m2/d and a storage coefficient of 0.003. Tracer tests show the aquifer is more permeable in a NE-SW direction; this observation is supported by the spatial distribution of transmissivity values from the Theis analysis. Piezometer tests provide data about the variability of transmissivity and hydraulic conductivity within the aquifer. This information is useful in the development of digital models that are primarily used in graduate co...

Karstic gypsum problems at wastewater stabilization sites in the Black Hills of South Dakota

The Triassic Spearfish Formation contains numerous gypsum beds in which karstic conditions have developed in the Black Hills of South Dakota. The evaporite karst has caused severe engineering problems for foundations and water retention facilities, including wastewater stabilization sites. Two dramatic examples include the former sewage lagoons for the City of Spearfish and a proposed lagoon/wetlands facility for Whitewood, South Dakota.The Spearfish sewage lagoons were built in 1972 on alluvium above a thick gypsum layer, despite warnings from local ranchers. At one point during construction, a scraper became stuck in a sinkhole and required four bulldozers to pull it out. The lagoons started leaking badly within a year after completion; the southern lagoon was abandoned after four years because of leaks, and the northern lagoon could not provide adequate retention time for effective sewage treatment. Attempts at repairs, including a bentonite liner, were ineffective, and poorly treated sewage discharged beneath the lagoon’s berm into a nearby surface drainage. The lagoons were abandoned completely in 1980 after a large lawsuit, and a mechanical wastewater treatment plant was constructed nearby.The planned Whitewood sewage lagoon and artificial wetlands were proposed in 1988 at an area with troubling similarities to the failed Spearfish site. Field investigation showed gypsum outcrops within proposed wetland cells and 10-m deep sinkholes nearby. After an engineering report cited these difficulties, subsequent drilling at a proposed wetland cell showed a 9-m thickness of gypsum that was exposed at the surface. The wetlands project and later the lagoon project were tabled after controversy.