The cleanup of radioactive contamination at the Hunters Point Shipyard was marred by widespread fraud, faked soil samples, and a high-pressure culture where speed was valued over accuracy and safety, according to four former site workers.

On Thursday, the four whistle-blowers, including a radiation safety officer who reported directly to the Nuclear Regulatory Commission, gathered with environmentalists to describe the problems with the cleanup, which has cost the federal government $600 million. In the background, construction crews were at work redeveloping the property, where 1,200 units of housing, millions of square feet of commercial space and hundreds of acres of parks are planned.

David Anton, an attorney for the workers, said the Navy and the Environmental Protection Agency — as well as the district attorney and state attorney general — should immediately launch investigations into the cleanup, a process that should include interviews with former workers and the retesting of the soil at the site. Also, the nonprofit Greenaction for Health and Environmental Justice filed a petition with the NRC to revoke the license of contractor Tetra Tech, which oversaw the cleanup at the Superfund site.

“Talk to the workers who were involved in the fraud. Find out what fraud was taking place, and then test and sample based on reality,” Anton said. “The Navy has fought at virtually every step a real look at contamination at Hunters Point.”

Questions over the accuracy of the soil tests emerged in October 2012, when the Navy discovered that some results were inconsistent with results from previous samples collected in the same areas. While the dirt in question was identified as having been collected from beneath a lab used to conduct radiation tests on animals, an internal investigation found that in at least 386 cases it had been pulled from areas already given a clean bill for radiological contamination.

On Thursday, the former workers said soil samples from areas known to be highly contaminated were switched with dirt gathered from the foundation of an old movie theater, where there were minimal toxic chemicals. Anton alleges that at least 2,500 samples were faked.

Robert McClain, a radiation technician who worked at the site in 2005, said Tetra Tech management ordered him to increase the speed of a conveyor-belt system he operated — even though the soil carried by the belt could not be properly tested for contaminants at the faster speed.

“Management was production-driven,” he said. “They wanted to run it faster so they could get the soil moved. I was told by Tetra Tech officials that I didn’t know what I was doing. I have 25 years experience in the nuclear power business.”

In a statement, Tetra Tech spokesman Charlie MacPherson said the company “emphatically denies the allegations made by individuals at today’s news conference that Tetra Tech engaged in a cover-up of fraud on the Hunters Point Naval Shipyard.”

FivePoint Holdings, the company developing the property, said its “utmost concern is the safety of our residents and employees. We are confident in the oversight process of the Environmental Protection Agency and other local and state agencies to insure when we take title of a parcel it is up to the standard consistent with the designated uses.”

J.K. Dineen is a San Francisco Chronicle staff writer. Email: jdineen@sfchronicle.com

Twitter: @sfjkdineen