In September 2009, the U.S. Environmental Protection Agency (EPA) was notified of potential elevated levels of thorium at the site.  The Winnebago Tribe of Nebraska decommissioned and disassembled a drinking water treatment facility.  EPA was notified after the decommissioned tanks were sent to a scrap metal facility, but were denied acceptance of the scrap metal based on the detection of low levels of radiation.  The decommissioned drinking water plant, four drinking water tanks containing the greensand material, and the greensand media from the largest tank (that had been dumped out to be scrapped) are staged at the Winnebago Roads Department.  The area where the material is being staged is behind one of the Winnebago Roads Department’s buildings in a fenced area used to collect debris from the community.  The staging area is approximately 300 feet in length and approximately 100 feet in width.  The tanks are at the eastern most part of the staging area next to the scrap from the decommissioned plant’s frame and the pile of soil which was mixed with the greensand material from the largest drinking water tank.  The soil pile is a mixture of the greensand material from the largest drinking water tank that has since been scrapped and soil from the Winnebago Roads Department’s property to reduce exposure to the small amount of radioactive material.  The soil pile is about 10 feet tall and 20 feet in diameter at the base.

1.1.2.1 Location

The Winnebago Tribe is located in Winnebago, Thurston County, Nebraska, in the northeast part of the state.  The material is being staged at Building 54, the Winnebago Roads Department, Rural Route 1, directly east of Highway 75 and just south of the city of Winnebago.

Thorium-228 is a hazardous substance as defined by section 101(14) of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).  Thorium is a radioactive substance that occurs naturally in the environment.  It has been shown to cause an increase in cancers of the lung, pancreas, and blood in workers exposed to high levels in the air.  Samples taken of the greensand filter media from the tanks exceed background levels for radioactivity at the Site.

EPA conducted sampling of the inside scaling of the tanks, the greensand material in the tanks, and the staging area around the tanks where the material had been dumped from the largest tank.  The results of the testing showed elevated levels of thorium-228 from 354 to 430 pico-Curie per gram (pCi/g).  These levels were well above background and were between 0.32 percent and 0.39 percent by weight, which is above levels considered to be source material.  Source material is considered to be 0.05 percent by weight for thorium and uranium combined as defined by the Nuclear Regulatory Commission.

The EPA removed all greensand filter material from the four remaining tanks at the Winnebago Roads Department and any soil/filter media mixtures including soil under and around the tanks and the mixed pile of soil/greensand material near the decommissioned tanks.  The material from the tanks will be collected and the soil/media mixtures will be excavated, and all material will be transported to an appropriate disposal facility.

The EPA will remove all greensand filter material from the four remaining tanks at the Winnebago Roads Department and any soil/filter media mixtures including soil under and around the tanks and the mixture pile of soil near the decommissioned tanks.  The material from the tanks will be collected and the soil/media mixtures will be excavated, and all material will be transported to an appropriate disposal facility.