| When the Weldon Spring Chemical Plant was operational from 1957 to 1966, four unlined pits were constructed to store waste by-products from the uranium refining process. These wastes (called raffinates) were placed in the pits in the form of liquid and fine-grained sludge.
Raffinate pit sludges at the Weldon Spring Site were treated to provide a structurally stable waste form before they were placed in the on-site disposal cell. On-site Chemical Stabilization and Solidification (CSS) was identified as the most effective technology for treatment of the contaminated sludge. In this process the sludge was screened for oversize materials, then thickened with a polymer before it was blended with cement and fly ash and transferred as grout to the disposal cell.
To provide design data for the full-scale CSS plant, a pilot-scale facility was constructed in 1994 and a testing program implemented in 1995.
The CSS plant operated from June to November 1998, 24 hours a day, 7 days a week. The plant produced approximately 186,000 cubic yards of grout.
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