HANFORD — After catching a radioactive rabbit just north of Richland, Hanford workers now are on the hunt for a radioactive mouse.
Radioactive mouse droppings have been found in the same area where radioactive rabbit droppings were found earlier this month. About 60 mouse traps have been set, but the two mice caught so far have not been contaminated.
The Washington State Department of Health is monitoring the situation, but does not believe there is a danger to the public, said Earl Fordham, the department's regional director of the Office of Radiation Protection.
No contaminated droppings have been found near areas that are open to the public, said Todd Nelson, Washington Closure Hanford spokesman.
Because the mouse and rabbit droppings were found in the same area, Washington Closure Hanford believes the animals ate or drank a common source of radioactive cesium contamination. Another theory is that a mouse may have gotten into contaminated rabbit droppings.
When Hanford workers began finding radioactive rabbit droppings, they checked 18 rabbits that were trapped or shot with pellet guns. Just one was contaminated, and it was killed and disposed of as radioactive waste.
No more rabbits have been seen or caught in the area where the droppings were found, Nelson said.
All were near the 327 Building, where hot cells were pulled out and demolition began on the structure about six weeks ago. During the years that plutonium was produced at Hanford for the nation's nuclear weapons program, workers stood outside of the hot cells and remotely operated equipment to perform tests on highly radioactive material.
One theory is the rabbit might have sipped water in the building's basement that was sprayed during demolition to suppress dust.
Washington Closure put up a chain-link fence around the building and scented the perimeter with fox urine to deter animals from entering the area. It also used gravel and steel plates to cover places identified as potential sources of contamination.
More recently, Washington Closure has found contaminated soil around two excavators that were used to demolish the 327 Building and planned to cover it with gravel Wednesday.
In addition, the contractor plans to start below-ground demolition of the 327 Building and will drop the slab now at ground level into the basement to cover up any contamination.
Workers also are scouring the area for any material such as dropped food from worker lunches that might attract mice.
"We're trying to eliminate food sources and replace it with bait," Nelson said.
Looking for any source of contamination -- whether contaminated piping or animal droppings -- is part of the cleanup routine, Nelson said. The goal of Hanford cleanup is to stop the spread of radioactive and chemical contamination left from World War II and the Cold War, and safely dispose of it.
It's not a surprise that contaminated animal materials are found at Hanford, said Larry Gadbois, an Environmental Protection Agency scientist.
In 2009 there were 33 cases of contaminated animal material found on the 586 square-mile nuclear reservation site. The radioactive animal materials more commonly are found closer to the center of the site, however.