Midwest School, which closed last week for a possible gas leak, had a similar problem less than two years ago, the director of the Casper-Natrona County Health Department said.

The Natrona County School District about a year-and-a-half ago notified the health department that some Midwest School employees were reporting vague illness symptoms such as headaches and fatigue, Dr. Kelly Weidenbach said Tuesday.

Then, as now, the department worked with the school district, the Wyoming Department of Environmental Quality and the state health department to conduct an epidemiological investigation and monitoring for chemicals, Weidenbach said.

However, the investigation found nothing conclusive to link anybody's symptoms to anything specific, she said.

"So now of course we have a new issue, new information and we're looking very closely at that," Weidenbach said.

The Casper-Natrona County Health Department has been in contact with Natrona County Emergency Management, the school district and the Wyoming Department of Health, she said.

Weidenbach anticipates hearing results from chemical monitoring efforts this week, she said.

The towns of Midwest and Edgerton were built along with the development of the Salt Creek oil field, which was one of the nation's largest petroleum sources a century ago.

So concerns about chemicals aren't new in the towns or at the school.

Oil field and other workers are still looking for the source of the gas or gases that forced the school's closure. Teachers and staff are conducting the final classes of the academic year at the former North Casper Elementary School.