A plume of contaminated groundwater originating from Tooele Army Depot has slowed its expansion, according to the review board overseeing restoration efforts.
The depot’s Restoration Advisory Board and Technical Review Committee found that “sentinel” wells located on the outer edges of the plume have not detected unsafe levels of the primary contaminant, trichloroethylene, or TCE.
“If it’s moving, it’s not moving fast,” said Jon Fenske of the U.S. Army Corps of Engineers.
The U.S. Environmental Protection Agency requires TCE levels below 5 parts per billion in municipal drinking water. Some test wells near ground zero for the plume have recorded levels of more than 700 parts per billion, according to monitoring well data from the engineering firm, Parsons Corporation.
Groundwater contamination at the depot is the result of dumping into an unlined industrial waste lagoon, according to the EPA. Initial EPA reports from 1990 pegged the amount of groundwater contaminated in the plume at 37 billion gallons.
Trichloroethylene, which is primarily used in solvents, adhesives and paint remover, is a carcinogen and can cause birth defects in high concentrations.
Despite the size of the plume, which stretches about two miles beyond the origin sites, public drinking water has not been affected according to models provided by the advisory board.
The plume remains just over a mile shy of reaching wells on farms south of Grantsville, on the far side of the sentinel wells.
On March 30, the EPA announced it was seeking input on a potential restriction or ban on the use of TCE as a degreaser, spotting agent in dry cleaning and in consumer products.
Engineering firm Parsons Corporation is overseeing cleanup efforts at some of the pits, landfills and buildings at the depot that have the highest concentrations of TCE. Two processes, soil vapor extraction and air sparging, are being used to prevent continued contamination of groundwater.
Soil vapor extraction involves drilling a 2-inch line into soil above the water table and using a vacuum pump to pull contaminated vapors to the surface for treatment. TCE readily evaporates out of soil or air, which makes soil vapor extraction an efficient means of removal.
Once the contaminated vapor is pulled to the surface by the vacuum pipe, it is fed to a treatment unit and the treated air is discharged.
Air sparging uses a compressor to pump air into saturated soil below the water table. Air bubbles move through the soil, carrying contaminated vapor up to a soil vapor extraction unit.
Nathan Jones, the project manager from Parsons, said soil vapor extraction and air sparging have been successful in removing contaminant. According to 2014 figures provided by Parsons, soil vapor extraction and air sparging have removed more than 16,000 pounds of contaminant since 2010.
When the EPA first attempted to clean up the contaminated groundwater, it used a water treatment facility installed on site to purify the water, which was then pumped back into the ground. Jones described the method as ineffective because it didn’t address the source of the groundwater contamination.
“It’s like you tipped over a glass of orange juice and you’re sitting at the end, mopping up the spill,” he said. “Now we’ve picked up the orange juice (glass).”
The groundwater treatment plant, which hasn’t been in operation for a number of years, is also slated for demolition. A request for proposal will be sent out but no guidelines are in place for the way the facility will be torn down or the projected cost.
Bioremediation may also help with the cleanup but further research is required, according to Marc Sydow with the U.S. Army Corps of Engineers. Aerobic bacteria and mineral-based dechlorination are the most likely natural causes mitigating the spread of the TCE plume.
The presence of oxygen and methane provide the resources bacteria would need to thrive near monitoring well sites. The bacteria can metabolize TCE while consuming methane. Sydow said the groundwater will be tested for enzymes that would result from that co-metabolism.
On the south side of Tooele Army Depot, another cleanup effort is underway related to munitions that were buried or dumped in pits. According to Troy Johnson from the depot’s environmental office, various agents were improperly disposed of decades ago, including tear gas, mustard gas, nerve and vomit agents and incendiary bombs.
Most of the munitions were stored in 165 open pits and 60 burial sites have been removed or are being removed under current projects.
The proposed next date for the depot’s Restoration Advisory Board and Technical Review Committee is Sept. 9.