Workers with the Oak Ridge Office of Environmental Management (OREM) and its contractor UCOR have finished installing the first of three large sludge-settling tanks for the Mercury Treatment Facility at the site’s Y-12 National Security Complex. The tanks, each of which will be 38 feet tall and 15 feet wide with a capacity of 36,000 gallons, provide a visible sign of ongoing progress on the facility where much of the construction has so far been below ground.