Three supervisors say in court records they saw the man tasked with protecting workers at the nation’s largest coal ash spill destroy evidence of dangerous levels of toxic chemicals.

The supervisors – two construction foremen and a TVA-paid overseer – say in affidavits filed in U.S. District Court they saw separate instances in which Tom Bock intentionally destroyed or skewed air monitoring results and knowingly endangered workers.

More:Coverage of the TVA coal ash spill in Roane County.

Bock served as safety manager for Jacobs Engineering, an international government contractor.

Workers sick, dying

The firm was tapped by TVA and approved by the EPA and Tennessee Department of Environment and Conservation to manage the clean-up of the massive coal ash spill at the TVA Kingston Fossil Fuel Power Plant in the Swan Pond community of Roane County in December 2008.

More than 150 of the 900 workers employed at the height of the years-long clean up are dying or are dead, according to court records. Many of those sick workers and survivors of the dead are suing Jacobs.

USA TODAY NETWORK - Tennessee investigated the treatment of workers at the spill earlier this year and uncovered, among other things, secret videos showing fly ash being dumped from monitor filters before they were packaged for testing.

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The news organization’s probe showed workers were not informed of the dangers of working 70 to 84 hours a week in coal ash, which contains more than 26 toxic chemicals including arsenic and mercury and has been linked by the EPA to higher cancer rates. Documents and interviews showed workers were denied protective gear – in violation of the EPA’s order declaring the clean-up site a “superfund” operation because of the toxicity of the materials involved.

Federal law makes it a crime if someone working at a superfund site tampers with or destroys monitoring results while knowing to do so would endanger people. The U.S. Attorney’s Office has repeatedly declined to comment on whether the office has launched a probe on behalf of the EPA. The EPA also isn’t talking. Neither is TVA.

Russell Johnson, a state prosecutor, has said he is working with TDEC and the state Attorney General’s office to determine if he can legally mount a criminal case. A decision hasn’t been announced yet.

More:DA: Treatment of Kingston coal ash workers needs state, federal probe

More:Kingston coal ash spill workers treated as 'expendables,' lawsuit by sick and dying contends

Attorney Jim Sanders, who represents Jacobs and Bock, says the firm will defend itself in court. His firm is already attacking workers' experts in court pleadings.

Cover up, destruction alleged

The only way the EPA knew if workers – or the public – were being endangered by the toxic ash that smothered 300 acres was through monitoring and testing. Part of that process included outfitting workers in different areas of the massive site with mobile monitoring devices.

The devices captured fly ash dust swirling around the workers. The weight of the dust captured in the filters is key to accurate testing, according to EPA records, and tapping the dust out before packaging the filters for testing skews the results downward, masking the danger.

Robert Muse, site safety manager for TVA for 18 months at the site, said in his affidavit that it was his job – initially – to choose workers to be outfitted with the devices, package the devices and record the test results.

He began noticing dangerously high results for workers in a half dozen specific areas where the unprotected laborers toiled directly in wet or dry ash.

“The worst results spot was where they were mixing the ash with the lime to dry it out,” Muse wrote.

More:Trial set for 2018 in lawsuit by Kingston coal ash spill cleanup workers

More:DA: Treatment of Kingston coal ash workers needs state, federal probe

More:Safety manager in Kingston coal ash spill cleanup admits workers denied respirators, masks

He said he told Bock, who insisted only workers in “cleaner, less dusty areas of the site” be outfitted with monitors. Muse said workers were never warned of the test results showing dangerously high levels of toxic chemicals in their work area.

“If the readings were high, they were not returned to the employees,” Muse wrote.

The superfund order required Jacobs to turn over all personal air monitoring results to the workers who wore them. Dozens of workers have now said in depositions they were never provided results, even after they pressed for them.

Foreman: Filters caked in ash trashed

Danny Gouge, a construction foreman at the site from the beginning of the clean up and a long-time colleague of Bock’s, said in his affidavit he saw Bock toss into the trash monitoring filters that were caked in fly ash.

When he prodded, Gouge said, Bock told him the workers were trying to sabotage the test results. He said he saw Bock shred documents. The EPA order required TVA to maintain all records related to the clean up.

Gouge also contends Bock knew long-term exposure to fly ash was dangerous.

“During my work at the site, Mr. Bock told me that if people really knew how bad this stuff was, the fly ash, they would quit work at the site,” Gouge wrote.

Gouge is now sick with a variety of ailments also suffered by many of the workers he supervised. Records show he joined the lawsuit after USA TODAY NETWORK - Tennessee revealed the findings pf its probe and the status of the case in court.

Masks destroyed, supervisors say

Michael Robinette, also a foreman, said he bought dust masks for flaggers who constantly inhaled fly ash. Bock ordered them destroyed, he wrote in his affidavit.

“He said that the site was a (superfund) site and that if they wore dust masks or respiratory protection it would change the status of the site,” Robinette wrote.

Robinette believed him. He joined the case after USA TODAY NETWORK - Tennessee reported that the EPA said in the superfund order that workers could wear masks or respirators if they chose and recommended them after testing results showed toxic exposure levels.

In a fourth affidavit filed by attorneys John Dupree, Keith Stewart and Jim Scott, Bock is accused of ordering Ernestine Sargent to stop giving workers dust masks and to destroy the ones she had in a supply room.

Sargent wrote that she went to TVA supervisor Dwayne Rushing to object, but Rushing responded, “If that is what Jacobs tells you to do, do it.” She said she then went to TVA site manager Gary McDonald, who ordered her to destroy the masks. She did, she wrote.

Jacobs: Prove it

Jacobs, represented by two of the nation’s most prominent law firms, is arguing in its latest court filings a jury should never hear testimony from Sargent and the supervisors because the workers’ experts have not yet revealed proof of a direct link between the coal ash to which they were exposed and their sicknesses.

Attorney Dupree countered the newly revealed tampering allegations make suspect the test results that workers’ experts need to prove that link. He’s asking for a delay in the January trial.

TVA agreed to pay Jacobs’ legal bills if the firm wound up on the losing side of lawsuits related to the clean up. Jacobs’ has invoked the agreement, even while trying to shift legal blame to TVA via a comparative fault defense.

Jacobs is now dropping that defense. Attorney Joe Welborn wrote Jacobs can’t find enough evidence to legally blame TVA, which gave the firm authority over the site.

“Upon review of the record to date, Jacobs agrees that it will not pursue as an affirmative defense the comparative fault of other entities,” Welborn wrote.