Work by the EM Office of River Protection (ORP) to provide additional groundwater protection at one of the Hanford Site’s groupings of large underground waste tanks is nearing completion.
An evapotranspiration basin being built at U Farm will collect runoff from an asphalt surface barrier to be installed above the tanks. The surface barrier will prevent precipitation from soaking into the ground and reaching deep soil around the tanks, which could mobilize contaminants toward the water table below.
Underground pipes connected to the surface barrier will collect the runoff and disperse it equally across the basin, where it will evaporate and transpire through plants in the basin as they release water vapor to the atmosphere. The bottom and sides of basin are lined with three layers of thick plastic, so the runoff won’t seep into the soil below.
“We have pump-and-treat systems in place to protect groundwater, and these interim surface barriers add another layer of protection for the groundwater and the environment,” said Becky Blackwell, EM ORP program manager.
With the completion of the basin at U Farm, Hanford Site tank operations contractor Washington River Protection Solutions (WRPS) will have built evapotranspiration basins for four tank farms. According to WRPS construction manager Jeremey White, the U Farm project is running ahead of schedule, thanks to an experienced workforce and applying lessons learned from previous projects.
“We were fortunate to hire a subcontractor that has worked with us on a previous evapotranspiration project,” said White. “There were a few days that weather prevented us from working, but even with those delays we stayed ahead of schedule in large part because more than half of the crew and leadership are experienced with the work.”
Other lessons learned include waiting until the weather cools in the early fall to begin planting the native plants and grasses in the basin. In addition to removing water through transpiration, the vegetation will also stabilize the soil in the basin.
Now that installation of the basin is nearly finished, WRPS and its subcontractors are focusing on preparing U Farm for installation of the asphalt surface barrier. Worker are removing legacy equipment from past operations and installing the piping that will carry runoff to the basin.
The slope of the U Farm will also be changed by adding clean fill dirt to help water flow from the barrier to the basin through collection pipes. This work will prepare the tank farm for installation of the interim surface barrier, which is scheduled to begin next year.
You can see an animated illustration of how the basin works here.
Original source can be found here.
