COLUMBUS, Neb. (AP) — A $3.4 million cleanup effort has begun at three sites linked to groundwater contamination in Columbus.

As of Wednesday morning, one of three buildings had already been demolished. A Missouri-based company hired as the main contractor will continue working with local contractors to demolish the other buildings over the coming weeks.

The remediation project is the result of the U.S. Environmental Protection Agency ordering the city to control a plume of tainted groundwater that originated more than 30 years ago on the former dry cleaner properties.

The agency identified the properties as the source of two carcinogenic chemicals that leached into the soil and groundwater over three decades ago, creating a contamination plume.

State health officials initially identified the groundwater contamination in 1983.