On July 17 and 18, 2016, a fast-moving, naturally caused wildfire burned over the 360-acre Edgemont, South Dakota, Uranium Mill Tailings Radiation Control Act (UMTRCA) Title II disposal site. The U.S. Department of Energy Office Legacy Management (LM) learned of the event early July 19, 2016, from a local rancher, whom LM permits to graze cattle on the site in return for fence maintenance and reporting local events that affect the site. Although the cell and the engineered erosion-control structures were unlikely to have been damaged by the wildfire, photos provided by the rancher and follow-up discussions indicated damage to the site’s surface features (e.g. fences, signs, grass) was likely. On July 22, LM visited the site to verify the fire’s impact, ensure the site was safe, and determine if any repairs were needed due to the fire or fire-fighting efforts.

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View to the east. A granite site marker is visible left of the vehicle and a new fire break
begins half way between the vehicle and the white-rock runoff-diversion channel.
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Numerous jackrabbits were observed after the fire, mostly near unburned vegetation within
the riprap areas, but several were in deep burrows in the middle of burned areas.

The 100-acre disposal cell is located about 2 miles south of the city of Edgemont, in southwestern South Dakota. Between 1986 and 1989, approximately 4 million tons of uranium mill tailings, contaminated soils, building debris, and contaminated material from 251 vicinity properties were placed in the disposal cell during remediation of the Edgemont mill. The cell is designed to be protective for 200 to 1,000 years. The 9-foot-thick cell cover consists of a low-permeability radon barrier (first layer placed over compacted tailings) consisting of compacted clay; clean, compacted fill; and a layer of topsoil material. The top of the cell and surrounding disturbed areas were seeded with native grasses. The cell design includes ditches that divert runoff water away from the cell cover.

The annual site inspection, required under the U.S. Nuclear Regulatory Commission license for UMTRCA Title II sites, took place only 5 days before the wildfire, and determined that the site was in good condition. Approximately 100 head of cattle were counted on the site during the inspection. After the fire, when asked about the cattle, the rancher stated he did not know how they did it, but, “Not one cow was harmed!”

The post-fire inspection found minimal site damage. An entrance sign post had been bent by a bulldozer that had entered the site to clear a 150 foot section of vegetation to create a 20-foot-wide fire break. The rancher will reset the sign post. Bulldozer work stopped before reaching the tailings containment portion of the site. The barbed wire perimeter fence was in good condition—one small section had been damaged when the bulldozer entered the site, but was repaired by the rancher. The roots of the plant systems appeared to be in good condition and should continue to prevent soil erosion.

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The granite marker providing information about the site is designed to outlast all other
signs and institutional controls.
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View toward the south from the northwest corner of the site. Signs were unharmed by
the wildfire.

The fire appears to have been beneficial, as it consumed a large quantity of brush, thus preventing a more damaging fire in the future. Wildfires occur naturally on open prairies and are important to maintaining the ecosystem.

The wildfire at the Edgemont site may also benefit LM’s pollinator initiative. The fire removed live and dead vegetation that competes with seedlings, creating an opportunity to seed pollinator species with a greater chance of success. A seed mix developed to support wild bee populations in the region could be broadcast over the site’s burned areas. This would be a relatively low-cost project, as the seed could be spread onto the ground without soil preparation or amendments. This would support LM’s goals to increase the diversity of desirable native plants in disturbed areas of the site and to provide habitat for pollinators.

LM confirmed that the fire did not harm any of the disposal cell’s engineered features and will continue to monitor the site to ensure that the cell remains protective of human health and the environment. The site will be inspected for any effects from the fire, specifically possible erosion caused by plant loss. Any ecological benefits resulting from the fire will be documented. Areas damaged by the new firebreak will be reseeded and the berms created will be graded to prevent channeling runoff. A September 2016 site visit was planned by LM ecologists as part of a noxious-weed control program, but the focus was shifted to the ecological effects of the fire.

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Site condition 5 days after the fire. This interior fence is used for grazing and is not part of
the perimeter fence system. It will be repaired by the grazing permitee.
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Vegetation is recovering 7 weeks after the wildfire.