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.