A water treatment plant in Gilbert was evacuated Friday because of a hazardous materials situation on Friday.
Jennifer Alvarez, digital media and marketing officer for Gilbert, said in am email to ABC15 that a "minor equipment failure" resulted in "a small release of ozone" at the plant.
Up to thirty people were in the area at the time, a spokesman for Gilbert Fire Department said.
Three people were transported to the hospital, said Alvarez. The other people were treated on-site.
The plant has since been given the all-clear, she said, and emplyees have returned to work.
The SanTan Vista Drinking Water Treatment Plant is located near Ocotillo and Recker roads. According to the Town of Gilbert, the treatment plant receives water from Central Arizona Project's Colorado River watershed through a 14-mile ductile iron pipeline.
The plant treats 24 million gallons of water a day, which is split evenly between Gilbert and Chandler, the website said.
The plant is undergoing an expansion project that began in 2016 and is slated to be completed in 2018.