The barriers help prevent rain and snowmelt from intruding into underground storage tanks and percolating into the soil, driving existing contaminants closer to groundwater. The temporary structures are to be constructed under an agreement between the DOE, Washington Department of Ecology, and U.S. Environmental Protection Agency. They will remain in place until a final closure decision is made for the tank farm.
SX Tank Farm is one of 18 groups of tanks, or “tank farms,” at Hanford. The site has a total of 177 underground tanks containing about 56 million gallons of chemical and radioactive waste left over from plutonium production during World War II and the Cold War.
Crews are working on a lined evapotranspiration basin — slightly smaller than two football fields — to collect and evaporate water drained from the barriers.
“This has been a huge undertaking, and the team has done a great job in overcoming many obstacles, including the removal of underground utility pipes,” said Jan Bovier, tank closure program manager for EM’s Office of River Protection.
The next phase will be construction of the two barriers, formed of a layer of gravel covered with a four-inch layer of high-density modified asphalt. Installation of the two barriers is planned to be completed during this fiscal year.
Several factors are considered during design and construction of the barriers. They include the weight of the barrier, which is tied to tank dome loading limits; working around in-place monitoring equipment, risers, and breather filters; and routing of the drain pipe from the barrier to the basin.
SX will be the third Hanford tank farm to have interim surface barriers. The others were constructed in T and TY farms in 2008 and 2010 respectively.