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POCATELLO — The FMC plant outside Pocatello has been closed for six years, but the industrial site still troubles the Environmental Protection Agency.
The EPA has been concerned with contamination at one of the site’s capped ponds for more than a year. In 2006, officials discovered worrisome amounts of phosphine gases in air samples taken from the area through the use of temperature-monitoring ports.
Now FMC believes it has developed a solution to eliminate the harmful gases from the ambient air, and the company is waiting for approval from the EPA in order to carry out the submitted plans.
In 2006, federal officials filed a legal order mandating FMC to install a gas treatment system on Pond 16S, which is now covered with soil and native grass and resembles a hill.
FMC recently submitted the “100 Percent Design,” which is a gas emissions treatment system to eliminate harmful gases from the pond.
“We have a perimeter system that is designed to collect gas,” said Jim Sieverson, remedial project manager and the only remaining FMC employee in Idaho.
The treatment plan is called 10X, and FMC officials said it will effectively bring the phosphine output to below the .3 parts per million limit required by the EPA.
The company had been working on a treatment system and is currently using a trial system for the new design, which has proven effective. The system in place now is a small-scale version of how the new treatment will work.
A pipe runs from the pond that is well below the surface of the ground to one of the temperature-monitoring ports above ground. It is currently mixed with oxygen to dilute the phosphine gases being sucked up the tube.
The gas is then transferred to a filtration system that cleans the phosphine gas into clean carbon, which is then harmless to dispose.
The system currently uses 55-gallon drums to store the filtered gas, but if EPA approves 10X, Sieverson said those storage drums will be replaced by a 10-foot by 10-foot storage unit.
If the process is expanded to a larger storage tank, FMC will mix nitrogen instead of oxygen with the phosphine in an effort to slow any chemical reactions that may cause the phosphine to rise too quickly.
“Instead of having air coming in, we’ll bring in nitrogen, which is inert (not chemically active),” Sieverson said. “We think that ought to help stabilize the reactions.”
The EPA is scheduled to respond to FMC’s proposal Sept. 4.

Jim Sieverson, the last FMC employee from the old plant and remedial project manager, is at a pilot plant for removal of phosphine gases that are coming out one of the capped ponds at the old site. According to FMC officials, a proposed treatment plan called 10X will effectively bring the phosphine output to below the .3 parts per million limit required by the EPA.
DOUG LINDLEY / IDAHO STATE JOURNAL