Students and staff won't be able to return to Midwest School until next fall at the earliest, a Natrona County School District spokesman said Wednesday.

The district closed the kindergarten-through-12th-grade school on May 25 after reports that an old well released toxic gases.

In June, the Casper-Natrona County Health Department reported the ATSDR, a division of the U.S. Centers for Disease Control and Prevention, found the air quality issues "constituted an urgent health hazard and that school officials and others who determined that the school needed to be evacuated were right in doing so."

Some areas of the school were deficient in oxygen. Gases included very high levels of carbon dioxide, and one classroom that had a level of benzene 200 times more than guidelines from the Agency for Toxic Substances and Disease Registry guidelines.

Wednesday, Natrona County School District Spokesman Kelly Eastes said GeoSyntec, the company hired to develop a remediation plan, will have that ready by Friday for review by agencies such as the health department.

The district expects the agencies to approve the plan in January, and hire a contractor to get in the building as soon as possible.

The contractor will install alarms, mitigation and monitoring systems ready for testing by April, he said.

"Once they start testing it, I'm not sure what that window is, it would slide into May before they would get the test results back, is what it sounds like currently," Eastes said.

Some seniors would like to graduate in the school, but that depends on the safety of the building and that has yet to be determined, he said.

The approximately 150 students and teachers at Midwest School have been attending the Pathways Innovation Center for grades 9-12, and the old Westwood Elementary School for grades K-8, Eastes said.