Midwest School's air quality is clear from the county health department

The report, distributed by the Casper-Natrona County Health Department, found air quality was acceptable for all chemicals tested. After installing a vapor mitigation system, the district conducted tests inside and outside the school in May, June, July and October.

Samples were taken in the library, swimming pool, kindergarten, kitchen and two classrooms. They were also taken outside to the swing set and the weather station.

Originally scheduled for Oct. 21, the most recent test was moved to Oct. 7 because of an unknown odor in room 105 — which was not one of the sample locations in previous tests — and because of fluctuations in carbon dioxide concentrations, according to the health department.

The students were moved out of room 105 on Sept. 20, according to the report. Dennis Bay, executive director of business services for the Natrona County School District, said there was a problem with the furnace in the room that gave off a gas smell, but that it had been repaired and the room was back in use.

Testing showed the classroom did not contain a high concentration of unsafe chemicals, and there will be no further sampling of the classroom, according to the health department's report.

Carbon dioxide alarms have been installed and activated throughout the school. A review of the CO2 concentration was carried out weekly for five weeks as part of “separate work arising from the resumption of school”, according to the report. These assessments stopped after the alarms were activated.

Bay said the fluctuations in CO2 were due to students filling the school again and breathing in, exhaling carbon dioxide and causing the concentration of the chemical in the air to rise.

“We understood what was going on there,” he said. “Everything has been great since then.”

Midwest School was evacuated and then closed in May 2016 after an odor was discovered and testing revealed a gas leak coming from an uncovered well in the nearby Salt Creek oil field. There are 120 abandoned wells on the 640 acres surrounding the Midwest, according to state records.

Many students reported having headaches and other symptoms at the time the gas leak was discovered.

Despite initial hopes that Midwest could reopen in the middle of the 2016-17 school year, the school remained closed until the summer of 2017. Students were bused to schools in Casper.

The district — with FDL Energy, which operates the Salt Creek field — installed a mitigation system designed to draw air from beneath the building into the atmosphere above it.

A similar incident closed the school's kitchens in November 2014. An odor was detected and two kitchen workers became ill. Local, state and national health officials conducted what they said was an exhaustive investigation and found nothing conclusive.