Hanford Site officials plan to pile waste above grade at the massive central Hanford landfill to expand its capacity rather than digging a new waste cell immediately. Plans call for adding another 20 feet of layered waste and soil to the top of the Environmental Restoration Disposal Facility. Initially, ERDF was planned to stand about 50 feet above ground level at its highest once it is closed, capped, and revegetated. Under the new plan, which is expected to proceed immediately, ERDF will stand 70 feet high at its center when closed. “It was an innovative idea, a good idea by Washington Closure Hanford,” said Mark French, the DOE project director for ERDF and the river corridor.
The amount of waste that would be added to the landfill in a vertical expansion would be about equal to the waste that could be disposed of in one of the landfill’s supercells, saving about $30 million in construction costs, according to Washington Closure. It also would mean a smaller footprint for the landfill. ERDF is made up of supercells measuring 500 feet wide and 1,000 feet long, along with regular cells half that size. The landfill now has the equivalent of six supercells, all of them 70 feet deep. ERDF is at the heart of cleanup at the DOE site, with low-level radioactive and hazardous chemical waste brought to the lined landfill for disposal and sometimes treatment. Washington Closure, which operates ERDF, has hauled in much of the waste the landfill holds as it has torn down buildings and dug up burial grounds and contaminated soil in the river corridor.
Now ERDF’s cells, which have about 18 million tons of total capacity, have just a half-ton of capacity left. “We are just about to the point of filling those cells to a point where we need to add capacity to continue cleanup work,” said Stacy Charboneau, DOE manager of the Richland Operations Office. The last construction on the landfill was two supercells built with American Recovery and Reinvestment Act funding. By mounding waste higher, the Department of Energy can delay adding another supercell, but will still need to have a new one ready for use in about 2019. All current cells and ones to be built would be included in the vertical expansion.
Calculations have been done to confirm to the Environmental Protection Agency that more waste could be piled on ERDF without damaging the landfill’s bottom liner or leachate collection system. As ERDF cells have been filled, the earliest ones have had a temporary cover of high-density polyethylene and soil added to prevent precipitation from intruding into the waste. The temporary cover will have to be either removed or the polyethylene breached by running bulldozers over it to cut holes in the material. Removing or cutting holes in the cover would allow any water, such as rainfall that falls on the landfill and could become contaminated, to be captured in the leachate collection system at the bottom of ERDF.
The landfill has been designed to have a slight crown at its center to ensure water flows off to its sides once ERDF is closed, said Dave Einan, an EPA engineer. The vertical expansion will keep the same design, with a 2 percent grade from the landfill’s center toward its ends and a 12 percent grade for the side slopes. Because of the size of the landfill, raising it 20 feet higher is not expected to create a significant visual difference, according to DOE. Central Hanford is expected to have other waste disposed of above ground level. Plans call for collapsing in the walls of processing canyons after the structures have been cleaned out. The concrete from the downed walls would be covered with an earthen cap, rather than hauling the demolition debris to a below-ground landfill.
