The Flat Top Mine Site is northeast of the town of Ludlow, Harding County, South Dakota (Attachment 1). Uranium mining activities occurred around Ludlow in the North Cave Hills, South Cave Hills and Flint Buttes from the late 1950s to 1964 under the General Mining Laws and Public Law 357, which did not require any restoration. The North Cave Hills and South Cave Hills are part of the Custer National Forest and subsequently owned by the United States Forest Service (USFS). The Flat Top Mine is located in the Flint Buttes and is currently on private ranch land.
Site assessment work conducted in 2009 and 2011 showed that the highest concentration of contamination occurred at and around an old mine pit on the north side of an old highwall, approximately 0.5 miles north of the town of Ludlow. Uranium was detected in soil sediments with concentrations up to 770 parts per million (ppm) and in surface water with concentrations up to 558 micrograms per liter (µg/L). Other elements of concern with elevated levels in the surface water were arsenic with concentrations ranging from 457 to 536 µg/L, vanadium with concentrations ranging from 73 to 258 µg/L, and molybdenum with concentrations ranging from 894 to 1,730 µg/L.
In 2012, two water wells were drilled to replace livestock water supply. The old pit mine, which had mostly dried up by 2013, was drained of precipitation water and backfilled with approximately 85,000 cubic yards of tailings. The backfill was capped with soil and revegetated with hydroseed.
In 2024, additional soil sampling for heavy metals and radioisotopes was conducted to determine if additional cleanup was needed. EPA is planning to conduct additional cleanup in summer 2026; updates will be posted to the Notices page of this website.
