One of the capped waste ponds at the abandoned FMC Corp. elemental phosphorus plant next to the J.R. Simplot Company phosphate fertilizer complex west of Pocatello, Idaho, is emitting phosphine gas, prompting the U.S. EPA to take emergency measures to monitor it.
The adjacent FMC and Simplot properties are on the Eastern Michaud Flats Superfund site, which covers 2,530 acres. In 1976, the Idaho Department of Health & Welfare conducted a groundwater monitoring study down from the plants, showing elevated levels of arsenic, lead, and cadmium above federal drinking water standards. Further sampling during the 1980s confirmed the results, and the site was listed on the National Priorities List in August 1990.
EPA conducted an informational meeting at Pocatello City Hall on July 12 to explain the status of FMC Pond 16S, which it determined was the most immediate concern after it inspected the property following the FMC plant’s closure in December 2001. The pond is generating a very high concentration of toxic and flammable gases under its cap, said Greg Weigel, EPA project manager.
FMC observed the phosphine gas in February 2006. The following June and September, a temporary monitoring point noted intermittent smoke at very high levels, ranging from 100,000 to 300,000 parts per million. In November, FMC sealed temporary monitoring covers, Weigel said.
In November and December, EPA’s analytical data confirmed very high concentrations of phosphine, hydrogen cyanide, and hydrogen sulfide. In December, EPA ordered FMC to characterize the gas generation problem under the Pond 16S cap and conduct ambient air and cap leak detection monitoring.
It also told FMC to design, build, and operate a gas extraction and treatment system to reduce gas concentrations under the cap to safe levels. Since April 2007, FMC has built and is operating a mobile gas extraction and treatment system onsite. It has submitted a preliminary design analysis for a larger extraction and treatment system.
Soil gases near the pond also were detected last May and June, indicating that a high concentration of phosphine gas continues to be generated in Pond 16S, but phosphine and other toxic gases were not detected in the ambient air.
Starting the week of July 16, Simplot was to install new wells to develop a final groundwater extraction system to capture water from its gypsum stack and continue to investigate the area’s hydrogeology. EPA officials said groundwater flowing from the Simplot and FMC plants toward Batiste Springs contains phosphorus and arsenic.
In June, an EPA official said Simplot is the main source of phosphorus entering the Portneuf River, discharging 1,200 pounds of it into the river each day. Too much phosphorus can lead to accelerated plant growth, algae blooms, and low dissolved oxygen that can kill fish. A Simplot official said the company is working to reduce by 80 percent its phosphorus discharges into the river.