SIOUX CITY, Iowa (AP) – Two workers at Sioux City’s wastewater treatment plant are no longer employed by the city.  Human Resources Director Bridey Hayes confirmed to KTIV-TV that superintendent Jay Niday and operations supervisor Pat Schwarte no longer work for the city. Hayes said she couldn’t comment further about their departure.

It’s unclear if the employees’ departure is connected to an ongoing investigation by the Iowa Department of Natural Resources. The agency is investigating whether an employee changed chlorine levels in wastewater samples to meet standards outlined in a state-issued permit that allows treated wastewater to be discharged into the Missouri River. City officials have said they are cooperating with the state and the U.S. Environmental Protection Agency.