EM’s Office of River Protection (ORP) and contractor Washington River Protection Solutions (WRPS) finished work on a lined evapotranspiration basin — roughly the size of two-and-a-half football fields — to collect and evaporate water drained from new high-density, modified asphalt surface barriers to be installed later this spring over SX Tank Farm.
The interim barriers will help prevent rain and snow melt from intruding into the 15 underground tanks or percolating into the soil and driving existing contaminants closer to groundwater. The barriers are temporary structures to remain in place until a final closure decision is made for the tank farm.
Crews excavated approximately 28,000 cubic yards of earth for the basin, south of SX Farm. They placed a series of drain pipes on a special liner in the basin floor and covered them with three feet of backfill that was hydroseeded to grow a customized mix of native plants and grasses to help evaporate the water. Hydroseeding is a planting process that uses a slurry of seed and mulch as an alternative to the traditional process of broadcasting or sowing dry seed. WRPS’s Environmental Protection group identified plants with relatively shallow root structures that won’t extend deep enough to damage the liner.
Another major element of the project was the placement of nearly 800 linear feet of storm water collection piping.
Working with engineering drawings from the 1950s and ’60s was a challenge, according to WRPS Construction Manager Jeremey White.
“We found things were close, but not quite where they were supposed to be,” he said.
The team used ground-penetrating radar to help locate buried utility lines of all types — electrical, raw water, instrument/dry air, and drain lines. Once lines were found, the team determined the best route for weaving the large 18-inch drainage pipe through the maze of abandoned-in-place and in-service lines.
Advanced planning helped workers to avoid cutting in-service lines, but extensive cutting and capping of abandoned lines was required, with all the necessary safety precautions.
“We were prepared to deal with high contamination, asbestos, and airborne radioactivity,” White said.
Workers installed three catch basins, three stormwater vaults, and a wastewater separator. The vaults, designed to handle output from a 100-year flood, weighed nearly six tons each.
“This has been a huge undertaking, and the team has done a great job in overcoming many obstacles as we continue to make progress on this project,” ORP Tank Closure Manager Jan Bovier said.