CORTLAND – Classes will return to normal today at Cortland Elementary School after foul odors from the nearby Waste Management landfill sickened teachers and students Tuesday.

Firefighter/paramedics from around the area took people from the school to Kishwaukee Community Hospital, and hospital officials said more than 60 people in all were treated for low-level carbon monoxide exposure.

Firefighter/paramedics from around the area took people from the school to Kishwaukee Community Hospital, and hospital officials said more than 60 people in all were treated for low-level carbon monoxide exposure.

William Zaver watched fellow students in his fourth-grade class develop sore throats after the overpowering odor moved through the school Tuesday morning.

"I saw three people in my class get sick," 10-year-old William said. "It smelled a lot like gas."

DeKalb District 428 staff noticed an odor at the elementary school just before 10 a.m., Superintendent James Briscoe said. Waste Management spokeswoman Lisa Disbrow said a contractor performing maintenance work at the landfill hit a pocket of old decomposing garbage, releasing the odor, but no methane gas, into the air.

"Any future work will be performed only when favorable conditions exist or the school is not in session as we complete this construction project," Disbrow said in a prepared statement. "We hope to have this project completed in the next two weeks, again based upon favorable conditions."

Officials had not determined late Tuesday what chemicals caused the odor. Neither the school's nor the landfill's hydrogen sulfide monitors went off, and firefighters did not find carbon monoxide at the school.

An inspector from the Illinois Environmental Protection Agency's Bureau of Land will visit the site today, agency spokeswoman Kim Biggs said. Biggs said Waste Management officials described a heavy, sour odor.

The wind carried that odor to the school less than a mile to the northeast, where it got caught in the ventilation system, Briscoe said.

"Our ventilation system is good, but it was just so concentrated," Briscoe said. "We opened doors, and it wasn't long before you couldn't smell anything."

Despite school officials' efforts, 63 students and staff reported headaches, nausea, vomiting and other symptoms and went to Kishwaukee Hospital in DeKalb. About 530 students attend Cortland Elementary,

The nausea students and staff reported feeling Tuesday morning was because of minor carbon monoxide exposure, said Dr. Michael Kulisz, chief medical officer for KishHealth System.

Kulisz suggested parents monitor their children for headaches, nausea and vomiting for about 24 hours. Fresh air is the first course of treatment, but parents should use their judgment about whether they need to bring children into the emergency room to be given oxygen, he said.

According to Cortland Assistant Fire Chief Kelly Davis, when emergency crews first responded to the scene their tests for air quality showed no levels of any contaminants such as carbon monoxide.

"Our air quality monitoring showed no levels of anything at all," Davis said. "Not from the initial sweep through the time the last units left the scene."

The low levels of carbon monoxide were detected using an oximeter on students and staff who reported feeling ill. The doctor on the scene recommended those patients be taken to the emergency room, Davis added.

Parents were told Tuesday afternoon that they could pick up their children before the scheduled dismissal time if they wished, and those who could not be picked up early were taken to the cafeteria, where the ceilings are higher, until buses could take them home at the normal time.

"I got a voicemail from the school saying there was an issue," said Chris Fowler as he walked his son Rowan, 8, out of the school.

"It smelled like a dump," said Rowan, a second-grade student.

Firefighter/paramedics from several departments responded, including Cortland, DeKalb, Sycamore, Genoa-Kingston, Maple Park, Rochelle, Elburn, Burlington and Hinckley. Equipment on the scene included nine ambulances, three fire engines and one rescue squad, and they carried more than 30 emergency personnel.

Fire officials cleared the scene around 3 p.m. after being there for four hours, Davis said.

• Daily Chronicle News Editor Jillian Duchnowski contributed to this story.