CHEYENNE, Wyo. (AP) — A project to clean up groundwater contamination in a residential area near the Wyoming Air National Guard Base in Cheyenne is making progress.

The Wyoming Tribune-Eagle reports ( ) state and federal officials told residents Thursday that well samples show lower concentrations of potentially dangerous chemicals than were detected last year.

Hazardous chemicals, including trichloroethylene, that have been used on the base during the past several decades have leaked into the groundwater in that part of north Cheyenne during the past several decades. But the contamination doesn't present a direct health hazard since the base and nearby homes are hooked into the city's water system.

Data collected in September show the amount of TCE detected in the groundwater at various sites has decreased 40 percent to 93 percent compared to 2012.