U.S. Sen. Michael Bennet of Colorado has joined a growing list of Capitol Hill lawmakers demanding the release of a study that details fresh concerns about toxic chemicals that fouled an aquifer south of Colorado Springs, as well as the drinking water of millions of other Americans.

Bennet and a bipartisan group of 10 other senators sent a letter to the heads of the U.S. Environmental Protection Agency and the Department of Health and Human Services expressing concern that the EPA appeared to be suppressing the study. Such actions are “unacceptable,” says the letter released Tuesday by Bennet, D-Colo.

“Given the wide use … and presence of these chemicals in communities across the U.S., it is critical that this report be released without delay and that EPA act immediately to update its guidelines to ensure Americans are informed of and protected from the danger of exposure to these toxins,” the letter said.

The June 8 letter comes after the Agency for Toxic Substances and Disease Registry recently sought to publish a study revealing how perfluorinated compounds found in military firefighting foam could be nearly six times more toxic than current advisories indicate.

A White House staffer refers to the study as a “potential public relations nightmare” in emails between top EPA administrators, released to the Union of Concerned Scientists under a Freedom of Information Act request and first reported by Politico.

The emails framed the findings as being “extremely painful” for the EPA and the Defense Department.

The Pentagon already has identified 548 drinking-water systems around the world that are contaminated under the EPA’s current lifetime health advisory of 70 parts per trillion.

The new levels deemed immunotoxic in the contested research review are 12 parts per trillion.

U.S. Rep. Doug Lamborn, R-Colorado Springs, fired off a similar letter last month, demanding an explanation.

The chemicals – which have saturated the aquifer beneath Security, Widefield and Fountain – have been linked to cancer, high cholesterol and other health ailments.

Local water districts have spent at least $9 million responding to the water crisis, and the Air Force has allocated another $38 million to help supply clean drinking water to Security, Widefield and Fountain residents.