Work is proceeding quickly to extract the last, but toughest, of the vertically buried pipes filled with waste at the 618-10 Burial Ground at the Hanford Site in Washington state. “We’re currently making good progress. We are approaching 50 percent completion with no unplanned events,” said Mike Jennings, director of the 618-10 Burial Ground Project for contractor CH2M Hill Plateau Remediation Co.
Former contractor Washington Closure Hanford augured 80 of the burial ground’s vertically buried pipes before its contract expired in September. CH2M finished loading out some of the waste from that work and also faced the task of cleaning up 14 vertically buried pipes. They were left for last because they were made of thick steel, information not evident from a study of historical documents before cleanup of the burial ground began in 2011.
Washington Closure drove overcasings into the ground around the first 80 pipes, which were made of either corrugated pipe or five 55-gallon drums with bottoms removed so they could be welded into a single pipe. An auger was used to destroy the pipes and mix the soil within the overcasing, the waste, and bits of pipe together. It then was scooped out of the overcasing and mixed with grout.
But the auger did not work in tests on heavy-gauge steel piping. “The bit would just rotate in the ground,” Jennings said. Instead, CH2M used a plan it inherited from Washington Closure for cleanup of the last 14 vertically buried pipes, after adding its own controls to the project. The pipes are expected to be about 20 feet long and range from about 12 to 20 inches in diameter. Most Washington Closure workers on the project transferred to CH2M, providing an experienced crew for the work.
Workers initially dug up enough soil to leave the top 4 to 5 feet of each of the 14 pipes exposed. They then lowered a box with a hole in the bottom around each pipe and added grout to the box. A hydraulic shear on an excavator chopped up the steel pipe, with the soupy grout confining the contamination to within the box. The grout and waste mixture was loaded into casting boxes to harden and to be hauled to the Environmental Restoration Disposal Facility in central Hanford.
Work started in late January on the 14 vertically buried pipes at what Jennings called “a very deliberate pace to make sure workers understood the process.” Since then workers have dug down another 4 to 5 feet and are well along on remediation of the second elevation. CH2M anticipates working at four elevations to reach the bottom of the pipes.
CH2M plans to remove hazardous materials from the 618-10 Burial Ground and two nearby sites by the end of the current fiscal year, Sept. 30, with fiscal 2018 spent on work such as sampling and then backfilling. In addition to the last 14 vertically buried pipes, CH2M is removing the overcasings left from cleaning up the first 80 vertically buried pipes. Most of the waste in the 12 trenches also at the burial ground was removed before CH2M took over the contract. But segments of the trenches were too close to the vertically buried pipes to dig up until work advanced further on the pipes.
CH2M finished demolishing the trenches last week, leaving only some residual debris at the bottom of the trenches to scrape up. Since 2011 workers have removed a total of 2,201 drums of waste. They also have dug up miscellaneous waste, including a 20,000-pound chamber used to decontaminate equipment at Hanford’s 327 radio-metallurgy laboratory. Most of the waste has been deposited at the Environmental Restoration Disposal Facility, but about 1 percent has been set aside as possible transuranic waste that would need to be sent to the Waste Isolation Pilot Plant in New Mexico.
Two nearby additional waste sites were added to the project because work there would have interfered with cleanup at the burial ground. One is a small site once used to track soil contamination using cobalt as a tracer. The other was once used to dispose of liquid waste, including liquids with uranyl nitrate and petroleum distillates. Although the contaminated soil covers only an area 20 feet by 20 feet as measured at the ground’s surface, the column of contamination reaches to groundwater and will require excavation to 87 feet deep. The final dig site is estimated to be about 300-by-400-feet at the ground’s surface and include a 900-foot ramp to the bottom.
The waste disposed of in the 7.5-acre 618-10 Burial Ground was largely produced by research activities in the Hanford 300 Area from 1954 to 1963. Some of the drums found in the trenches were lined with concrete. A pipe nested inside the concrete was used to hold waste with higher levels of radioactivity. They likely predated the vertically buried pipes. Shielded trucks would be loaded with containers ranging from the size of juice cans to buckets holding radioactive waste. The trucks would be driven to the 618-10 Burial Ground and backed up to the vertically buried pipes to drop the waste containers into the pipes. The burial ground is 6 miles north of Richland along the main Hanford highway.
