EM Richland Operations Office (RL) and contractor Central Plateau Cleanup Company (CPCCo) recently completed actions to stabilize three at-risk underground structures on the Hanford Site’s Central Plateau.
Office of Environmental Management
April 20, 2021
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These photos show the largest of three aging underground structures, the Z-9 crib, before and after stabilization. The 60-foot-long covered trench for liquid waste disposal during past Hanford Site operations was filled nearly to the top with about 4,000 cubic yards of engineered grout to cover residual contamination and stabilize the structure.
RICHLAND, Wash. – EM Richland Operations Office (RL) and contractor Central Plateau Cleanup Company (CPCCo) recently completed actions to stabilize three at-risk underground structures on the Hanford Site’s Central Plateau.
“The project has met the objective of mitigating the release of contamination for an age-related collapse of the three structures,” said Al Farabee, Hanford’s senior technical advisor for the project. “Completion of this project is a significant step forward in our mission to reduce risk to workers and the environment.”
The three structures — the 216-Z-9 crib, 216-Z-2 crib and 241-Z-361 settling tank — are located near the former Plutonium Finishing Plant. All three underground structures received liquid waste during Hanford’s plutonium production operations and contain residual radioactive and chemical contamination.
The cribs are deep, unlined trenches in the soil, covered with wooden or concrete roofs, with pipes running into them for disposal of liquid waste. After waste flowed into the cribs, solids would settle to the bottom and liquids would be absorbed into the soil column over time.
Earlier this year, workers safely completed filling the two largest structures, the Z-9 crib and Z-361 settling tank, with engineered grout.
For the Z-2 crib, the project team identified additional soil above the crib that was not evident in the drawings or identified during field walk-downs. When this additional soil was considered in the revised risk analysis, it was determined that this thicker layer of soil provides proper protection in the event of a crib collapse.
Routine monitoring will continue to ensure all three structures remain stable in their current configuration.
“I am proud of our team for overcoming many challenges to complete this critical project,” said Bob Nichols, director for CPCCo’s Inner Area End States group. “As Hanford continues to advance this and other elements of its risk reduction mission, the safety of our workforce will continue to be paramount.”
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