The last of the 94 vertically buried pipes filled with radioactive waste have been removed from the Hanford Site’s 618-10 Burial Ground, and other cleanup work there is nearing completion, according to the Department of Energy and cleanup contractor CH2M Hill Plateau Remediation Co.
Former river corridor remediation contractor Washington Closure Hanford developed a plan for the pipes, called vertical pipe units, and started the work in 2009, with CH2M taking over when the prior river corridor contract expired in September.
Washington Closure dealt with 80 of the pipes, which were made of corrugated piping or 55-gallon drums with tops and bottoms cut off and welded together. It drove an overcasing into the ground around the pipes and then used an auger to cut through each pipe and mix the waste with the ring of soil within the overcasing. CH2M finished digging the mix of waste and soil out of the overcasings in February, mixing it with grout for disposal.
In May, CH2M finished removing the waste from the remaining 14 vertical pipe units made of heavy-steel that an auger could not break up. The soil was removed from roughly the upper 4 or 5 feet of all the units, after which a box with a hole in it was fitted over each pipe. A grout mixture was poured into each box to allow a hydraulic shear on the end of an excavator to break up the pipe with the grout without spreading contamination. The work was done in four progressively deeper layers for most of the pipes, with a fifth layer needed for four of the pipes that were slightly longer than the typical 20 feet.
All of the grouted waste from the pipe units was determined to be low-level radioactive waste and was taken to the Environmental Restoration Disposal Facility (ERDF) in central Hanford.
The waste came mostly from research and fuel development projects in the 300 Area of the then-plutonium production site in Washington state, with waste hauled to the vertical pipe units in heavily shielded cask cars from 1954 to 63. The trucks would back up to the pipe units and drop containers ranging up to the size of buckets down the pipes.
Meanwhile, CH2M has also wrapped up excavation of the larger of two soil waste sites near the 618-10 Burial Ground. Workers dug down to groundwater 67 feet deep, building a 900-foot-long ramp enabling trucks and equipment to reach the floor of the hole. Nearly 13,000 truckloads of soil were hauled out, said Tammy Hobbes, CH2M vice president for the 618-10 Burial Ground and ERDF. Some unexpected debris and higher levels of contamination than expected were found at the waste site, Hobbes said. Sampling will be done to confirm that enough contaminated soil has been removed before backfilling begins.
CH2M plans to start work next month on the smaller of the two waste sites, where radioactive tracers were used at a test site. Research was conducted there to evaluate how precipitation and other water would spread contamination in the ground.
The main focus now at the 618-10 Burial Ground is removing the remaining contaminated soil in a mass excavation effort, according to DOE. Some waste was deposited directly into the soil at the burial ground, and in March workers completed retrieval of 2,201 contaminated drums and other debris there. The remaining excavation effort includes digging up the overcasings used for 80 of the vertical pipe units and contaminated soil from around all of the former pipe units. The work is expected to be completed in September, allowing CH2M to move on to final steps, such as backfilling, said Bryan Foley, DOE project director.
Total cost for cleanup of the burial ground and two nearby waste sites is projected at $230 million to $250 million.
