Wash. Closure Works to Backfull Excavated Areas
WC Monitor
10/17/2014
Washington Closure Hanford is in the midst of a major backfill campaign as much of the Hanford river corridor cleanup nears completion. In the last 20 months, workers under a DelHur Industries subcontract have placed 3 million tons of backfill. That’s enough to fill an area the size of a football field 900 feet high, or about one-and-a-half times the height of the Space Needle in Seattle, said Ron Morris, Washington Closure manager for backfilling in the 100 Area. Massive holes have been dug, both near C Reactor and the D and DR Reactors, to chase chromium contamination in the soil down to 85 feet deep. The hole near the D and DR Reactors stretches over the size of more than seven football fields. At N Reactor, removal of contaminated soil left 98 waste sites that had to be refilled. As those and other sites are backfilled, Washington Closure is working to leave a natural landscape and preserve the clean soil used for backfill.
The landscape near Hanford’s former C Reactor may look mostly flat from a distance, but up close small ridges, indentations and rock outcroppings are more noticeable. That’s just what James Bernhard, a wildlife biologist and the natural resources lead for Washington Closure Hanford, likes. “Engineers like things square and flat,” he said. But he has made sure the heavy equipment used to fill what was essentially an open pit mine near C Reactor has not left the ground too tidy. It’s Bernhard’s goal for the finished backfill at that and other sites to mimic nature, not a soccer field. “Something flat has much less potential real estate,” he said. A naturally undulating landscape with rocks provides areas with shade for plants and animals, he said. It provides shelter from the Hanford-area winds. It catches seeds, helping them to take root rather than being blown away. It provides places for small animals, like mice and rabbits, to hide from predators, like coyotes. And it helps hold moisture better than flat surfaces, where wind evaporation is greater.
The majority of Hanford land is planned to be used for preservation and conservation as cleanup is completed. It is shrub steppe habitat, which has been described as one of the most imperiled ecosystems in the nation, said Paula Call, of the Department of Energy’s Site Stewardship Division. The 15 million acres of shrub steppe that once covered much of Eastern Washington has given way to agriculture, leaving just 5 million acres. Only three large tracts remain — the Yakama Nation reservation, the Yakima Training Center and Hanford. “The department does recognize the ecological value of the Hanford Site,” Call said.
Some Areas Left Shallower to Keep Costs Down
DOE and Washington Closure have found ways to reduce costs as large areas are backfilled. That has included backfilling some areas to just 86 percent, when acceptable to Hanford regulators. Some sites, including those near reactors, must still be filled to 100 percent. But leaving other areas a little shallower than before cleanup begins means less fill soil has to be dug up at borrow areas near each reactor and hauled to backfill sites. Historically, each reactor had a borrow area to provide dirt for construction, such as building roads. Now those borrow pits are part of Hanford Reach National Monument land along the south side of the Columbia River, and DOE’s goal is to remove as little additional soil from them as possible.
Washington Closure also is using uncontaminated debris for some of the fill to reduce the need for borrow area dirt. It has used concrete and steel from former Hanford service buildings and the metal rails from railroad tracks as fill material. That saves the cost of loading out and hauling the material to the Environmental Restoration Disposal Facility in central Hanford. And it helps conserve space in the landfill, which has been expanded several times across shrub steppe habitat. In some places, including between N Reactor and the Columbia River, stakes were placed to show crews how deep fill soil should be placed in different areas to create the final contoured, landfill. Heavy equipment operators are told just to leave dirt in piles and then the last step of sculpting the ground is done as vegetation is planted.
Work Completed on Largest Single Site
Work has been completed on the largest single backfill site at Hanford, the deep dig near C Reactor. “It was one big soup bowl,” Bernhard said. “It was the ugliest thing you ever saw.” A little more than 100 acres has been seeded with native grasses and planted with 52,000 big sage, spiny hopsage and antelope bitterbrush grown from seeds collected at Hanford. Backfilling near N Reactor has been completed and crews are starting to work on the area near the D and DR Reactors, the site of another dig down to 85 feet. The area near N Reactor will be seeded late this fall or in early spring. “I’m thrilled with what Washington Closure Hanford has done,” Call said. “It leaves the land in better ecological shape than when it started.”
