Nearly 30 children and one adult became ill last week when a plume of tear gas and pepper spray used at a police training exercise in the area drifted to a nearby elementary school in San Bruno, Calif., according to authorities.

At the time of the incident, nearly 30 students at Portola Elementary School reported experiencing symptoms including coughing, watery eyes, wheezing and trouble breathing, according to Matthew Duffy, superintendent of the San Bruno Park School District. There were also news reports of vomiting and rashes.

“More than a week later, we still have some students who are suffering adverse effects from the exposure to the tear gas and pepper spray in the air that day,” Duffy told the Los Angeles Times. “It is now well-documented that some families needed to get emergency medical assistance to support their children who were suffering from the effects of the gas in the air.”

The San Francisco Sheriff’s Office, which oversaw the crowd-control training exercise on May 21 and launched an investigation of the incident, has apologized to the students and their families as well as the faculty.

But Duffy said the district would be sending a “formal letter” to sheriff’s officials requesting a halt to all “gas-related” training at the facility, which is less than half a mile from the school.