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May 9, 2017
Hanford Site contaminated pipeline remediation
Owner/developer: Washington Closure Hanford
Team: Columbia Energy, engineer; American Rock Products, ready-mix supplier
Contaminated waste lines containing elemental mercury at the Hanford site’s 300 Area were filled with a sulfur-amended grout mix to help minimize the potential for mercury releases during excavation and segmenting of the lines for disposal.
Regulators were interested in utilizing sulfur to amalgamate mercury, which resulted in specifying a grout mix containing elemental sulfur. American Rock Products, along with Columbia Energy and Washington Closure Hanford technical staff, designed a non-segregating, flowable, sulfur-amended grout mix suitable for injecting into abandoned waste lines.
Mix-design efforts were carried out on small-volume test batches using powdered and pelletized sulfur along with different cement and slag contents before selecting a slag-based mix that incorporated powdered sulfur. Because of the sensitive nature of the remediation work, a flow testing was performed near the batch plant to demonstrate the ability to pump the mix a minimum of 500 feet through a 2-inch-diameter line.
Flow testing was successfully completed in 2013. The bulk sulfur was obtained in super sacks and added to the mix trucks dry at the plant, and then the trucks were batched with the remaining materials. Prior to injecting the sulfur grout into the contaminated lines, engineering designs were completed to define the injection and vent locations and connection details.
Approximately 2,900 feet of buried waste lines with residual radiological and mercury contamination were successfully filled with the sulfur grout mix between August and September 2014. The waste lines ranged from 2 to 6 inches in diameter and were filled in segments.
A standard pump truck was used to inject the grout into the lines at a controlled rate. Rupture discs were used on the grout-injection assemblies to prevent the grout pump from exceeding the design pressure rating of the grout delivery lines and fittings used to connect to the buried waste lines in the event of a line blockage.