The study, which is being conducted by the city and CVS Pharmacy, is related to the Bozeman Solvent Site on West Main Street. The contamination was caused by a former dry cleaner at the Hastings Shopping Center that disposed of the suspected carcinogen PCE through the sewer system.

Scott Dwyer is a senior toxicologist for Kleinfelder, an environmental consulting company hired to conduct the study. He says any PCE that migrated into peoples' homes from the site would not reach levels high enough to cause sickness.

But the indoor air study was ordered because a study over the summer found that PCE levels in the area exceeded the screening level set by the state Department of Environmental Quality.

About 10% of area structures are expected to be tested in the latest round.

CVS assumed responsibility for the site in 2006 as part of its acquisition of the Osco Drug chain.