GRAND RAPIDS, Mich. (WOOD) — The large, unmarked motor home-looking vehicle parked along Hall Street SE could help answer whether the air in the surrounding neighborhood is safe.

The bus is a mobile air analyzing rig brought to Grand Rapids after a plume of volatile compounds was found under the site on Hall east of Madison Avenue that used to house a dry cleaner. The dry cleaner closed in 1995 and has since been replaced by a new building. A vapor barrier was placed over the contamination before the new building went up.

But the plume spread under the older building to the west. In May, chemical vapors were discovered seeping through the floor. The affected building’s tenants, two nonprofit agencies and two apartments above, were evacuated and work is being done to clear the air.

The U.S. Environmental Protection Agency knew about the underground plume and had been monitoring it. It wants to make sure the problem is limited to the single building.

The air analyzing rig, essentially a lab on wheels, will help in that effort. It allows the EPA to roll into the neighborhood and check the inside air quality of buildings, specifically those up to about three blocks north of Hall, a block east of Madison and just beyond Lafayette  to the west.

“Initially, we were targeting 60 (properties) and we expanded that a little bit to reach out into a few more areas, so we went up to 75 properties,” explained Betsy Nightingale, the on-scene coordinator for the EPA.

The majority of those properties are residential.

“We are doing this as a precaution. I don’t anticipate seeing high levels in indoor air, but we want to check and just be sure,” Nightingale said.

The chemicals of concern are called tetrachloroethylene, or PCE, and trichloroethylene, or TCE. They belong to a family of chemicals derived from petroleum called volatile organic compounds. PCE and TCE can cause health issues such as headaches and dizziness. Long-term exposure may cause cancer, according to an EPA release from earlier this month.