The Shoshone-Bannock tribes have convinced the Environmental Protection Agency to take a second look at soil and water contamination from two phosphorous plants that operate within or near their reservation’s borders.

The federal agency will review cleanup plans for the Superfund site that includes the plants run by FMC, now called Astaris, and the J.R. Simplot Co. north of Pocatello. That could lead to stricter, more expensive cleanup requirements.

The tribes objected to the plan drawn up by the federal agency to clean up decades of soil and groundwater contamination from the plants, which extract phosphorous used in products like detergent and sodas and pesticides.

Two years ago, FMC was fined nearly $12 million by the EPA for blatantly mismanaging its hazardous waste ponds, which had caught on fire and released poisonous gases. The company also agreed to invest $190 million to help curb air pollution problems in one of the biggest settlements in the country.

The Superfund agreement, which is separate, targets historic soil and water contamination from the plants. Pollutants exceeding health levels have spread from the plants onto the Fort Hall Reservation, although that zone extends for less than a mile, said Wallace Reid, the Superfund site’s project manager for the EPA.

The agency decided to have more discussions before finalizing a consent order with the two companies. The tribes objected after the Justice Department entered the consent order with the court.

The EPA decided that some of the tribes’ arguments had technical merit, Reid said.

“Finally, years later they’re going to reevaluate some of the issues we brought up,” said Susan Hanson, who handles Superfund issues for the tribes.

Tribal members don’t want the companies to simply cap old waste ponds containing hazardous chemicals and phosphorous, which can ignite when exposed to air. Reid said the agency may look at using a different kind of cap, since new information shows the ponds contain higher amounts of phosphorous than previously thought.

The tribes also want the companies to clean up soil contamination, rather than simply erecting fences and signs warning people to stay out of those areas.

The agency will have to look at whether it’s legal to do that on reservation land, since that could negatively impact the tribes’ ability to develop it, Reid said.

The EPA also wants to flesh out how groundwater will be monitored and how to check for fluoride, which is released in the plants’ emissions, in soil and plants. Those two issues were left up in the air in the original cleanup proposal, Reid said.

“We’re taking about a year to look at these various issues,” Reid said. “My hope is that we have more of a broad outline so the tribes can be comfortable.”

FMC and Simplot have both asked a federal judge to order the original plan be implemented, claiming the time has come for action.

“The companies have spent about $40 million on studies,” FMC spokesman Tom Kline said. “Now we are in a position of really wanting to move forward.”

Simplot spokesman Rick Phillips said the U.S. Department of Justice is petitioning the EPA to sign off on Simplot’s part of the consent order so the company can begin work.

* The Associated Press contributed to this report.