(Reuters) - The U.S. government said on Tuesday it was delaying indefinitely its proposal for how to clean up or seal off radioactive soil buried in a St. Louis-area landfill adjacent to another waste site where an underground fire has been smoldering for several years.

The postponement by the Environmental Protection Agency, citing lags in receiving “technical documents” needed to formulate its plan, drew an outcry from local officials angry at the potential public health hazard posed by the site.

A remediation plan for the West Lake Landfill in Bridgeton, Missouri, about 20 miles (32 km) northeast of St. Louis, had been expected from the EPA by the end of this year.

But the EPA decided to “extend the timeline” to allow for further documentation and review by experts, the agency said. No new deadline was set.

“Given the complexity of this site and potential community impacts, we must ensure that sound science is driving our decision-making,” EPA regional chief Mark Hague said.

The West Lake site, originally used for agriculture, became a limestone quarry in 1939. But starting in the 1950s, portions of the area were used to dispose of municipal refuse, industrial wastes and construction debris.

In 1973, some 8,700 tons of leached radioactive barium sulfate from the Manhattan Project, the World War Two-era atomic bomb-development program, were mixed with 38,000 tons of soil used to cover trash dumped at the site, according to the EPA.

In 1990, the landfill and neighboring waste-disposal facilities occupying a total of 200 acres (80 hectares) were designated by the EPA as a single Superfund site.

Adding to concerns, a slow-burning chemical fire has been smoldering since 2010 beneath the surface of the adjacent Bridgeton Landfill, coming within 1,200 feet (365 meters) of the West Lake Landfill.

The company that operates both landfills, acting under EPA orders, has since installed a barrier system of heat-extraction wells and other safeguards to keep the fire from reaching the radioactive waste.

The EPA is now deciding whether to proceed with one of three remediation options for West Lake - permanently cap the waste and keep it isolated underground; remove some of the waste and leave a portion of it buried; or excavate all the waste.

St. Louis County Executive Steve Stenger expressed anger at the EPA’s postponement on Tuesday.

“It is extremely disappointing and hard to believe that there is yet another delay in EPA’s cleanup of the West Lake Landfill,” he said. “It is time for a permanent solution.”