Mario Cuestas, 53, is accused of dealing methamphetamine to high school students and committing sexual acts with a minor. He was arrested at his workplace last week and is being held without bail at the Santa Clara County Jail.
On Tuesday, he was in court on three charges of selling and possessing methamphetamine.
Cuestas is also accused of having a sexual relationship with a 17-year-old boy, but has not been charged in that case as the investigation continues.
"I think the essence of this case is it's an individual who occupies a position of trust in the community and who violated that position of trust by engaging in this type of criminal conduct," Santa Clara County District Attorney Patrick Vanier said.
Cuestas worked for the fire department for 20 years and was also a volunteer at a South Bay church.