"All of the soil samples were collected by EPA personnel, and the dust and swipe samples were collected by both EPA and Tetra Tech on mixed teams," said Ben Washburn, a spokesman for EPA Region 7, said in a statement. "In no case did Tetra Tech operate independently from EPA in the collection, storage, transport, or custody of the samples collected in Spanish Village."

The EPA has stated that tests of the samples collected are expected to take two months to process, and that Tetra Tech will not be involved with the analysis.

In the wake of its sampling violations in California, Tetra Tech reached an agreement with the NRC to avoid a $7,000 penalty under the condition that the company discuss "lessons-learned from the event" with its employees, conduct additional safety training and eventually consent to an independent assessment of the company's "safety culture." The NRC, which licenses Tetra Tech to conduct such work, notified the EPA of the commission's decision of enforcement in July, according to Diane Screnci, NRC public affairs officer.

But critics say the infractions are another reason they're troubled by the EPA's continued involvement with the company, adding to previous concerns about a possible conflict of interest, since Tetra Tech counts the landfill's operator, Republic Services, as a client.