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The U.S. Department of Energy (DOE) Office of Legacy Management (LM) completed a maintenance activity in August to stabilize a landfill at the Rocky Flats Site in Colorado. LM installed 267 ground anchors and more than 4,400 feet of subsurface drains to alleviate downhill slumping of the steep slopes of the Original Landfill. The project began in August 2019.

“The team did a great job keeping the project on schedule and within cost,” said LM Rocky Flats Site Manager Scott Surovchak. “This is especially noteworthy since the team had to change how they worked, adding more health and safety measures back in March in response to the COVID-19 pandemic.”

The Original Landfill was used as a construction and general facility waste dump from the start of the former Rocky Flats Plant operation in 1952 through 1968. During those years, trash was dumped onto the steep hillside, then covered with soil. Although the landfill was never intended to be used as a hazardous or radioactive waste disposal site, some hazardous materials such as paints, solvents, asphalt, and other chemicals were likely disposed there. When cleanup activities took place, DOE identified remaining areas of low-level radioactive material and removed them before the landfill was graded and covered. In 2005, new soil cover and drainage features were installed as part of the Rocky Flats Closure Project.

Original Landfill soil had been slumping downhill for the past several years, with previous repairs providing only short-term stabilization. To achieve long-term stabilization, the newly-installed system uses anchors to create resistance against land movement to prevent future slumping. This maintenance action was approved by the Colorado Department of Public Health and Environment in July 2019.

Each anchor includes an 8-foot by 8-foot by 18-inch, 12,800-pound concrete retention block connected to a stranded, steel cable anchor. Anchors extend between 54 and 130 feet into the hillside and underlying competent bedrock, with more than 24,300 feet of anchor length installed.

Subsurface drains were installed to intercept and redirect groundwater from the hillside to reduce instability caused by excessive groundwater in the slope. Along with subsurface drains, the project team used 1,721 tons of drain rock and installed 52 cleanout drains. Articulated concrete block and rock were also installed on the hillside to re-establish surface water controls.

Once the system installation was complete, perimeter channels and hillside berms were restructured. In the final project phase, approximately 20 acres were re-seeded with erosion control mats to re-grow vegetation. Re-seeding occurred on all disturbed areas within the Original Landfill waste footprint, which was less than 4 acres.

LM Strategic Partner (LMSP) Project Manager Harry Bolton led the project to completion.

“This team carried out their responsibilities while faced with, at-times, unforgiving site conditions and high-risk tasks, half of which took place during a global pandemic,” said Bolton. “To achieve this accomplishment took every person’s unwavering dedication paired with continuous oversight and a robust safety and health culture. Every team member should be proud of their performance. I have nothing but gratitude for every one of them.”

LM contractors and subcontractors performed more than 50,000 work hours with no Occupational Safety and Health Administration-recordable incidents and no lost-time accidents while adhering to established safety work controls. Worker risk of exposure to volatile organic compounds (VOCs) and radionuclides was low, based on Original Landfill closure data, comprehensive risk assessments, and intrusive work completed during the project’s design development.

LMSP Project Safety Lead Jerry Mattson describes the team’s commitment to safety as “extreme ownership.”

Mattson explained, “When you consider the magnitude of this project and the number of safe work hours, it is a testament to the team’s commitment to safety. Everyone should feel proud of the work they accomplished to help protect the public and the environment.”

On-site project management, safety oversight, and radiological protection measures reinforced worker protection and helped to contain VOCs and radionuclides. There was no risk of radiological exposure to the public during this project.