North Dakota's Health Department has confirmed that diesel fuel and antifreeze were introduced to water lines serving an apartment complex in Tioga.
The conclusion came after three rounds of water sampling. Officials last month determined that the general water supply in Tioga had not been contaminated.
The 20 residents of the apartment complex have been staying at hotels or with friends during the investigation. Wayne Kern with the Health Department says water to the complex remains shut off.
Officials speculate that a contractor put the diesel fuel and antifreeze in the lines to thaw frozen water pipes. The investigation is continuing and city officials say they are still deciding what to do next.