The Contra Costa County Chief of Emergency Medical Services was arrested Sunday on charges of possessing controlled substances, authorities said Tuesday.

EMS Chief Richard Stephenson has been placed on administrative leave after he was arrested by Martinez police for the alleged violations of California Health and Safety Codes.

"Preliminary investigation indicates this is an isolated incident that did not involve the public or affect our services provided to the public,” Jeff Carman, Fire Chief of Contra Costa County Fire Protection District said in a statement.

According to police documents the arrest came after the woman he was renting a room from in Martinez found dozens of vials of fentanyl and other drugs in a laundry basket while cleaning his room. She noticed other medications and hypodermic needles.

She brought the drugs to the Martinez Police Department with the intention of turning him in, police documents show.

Those same documents say Stephenson had access to pharmaceutical bins, fire trucks and other prescription drug disposal areas. Police believe he could have been selling the drugs on the street.

NBC Bay Area learned Stephenson my have needed help, himself. Those same documents say Stephenson was in detox at the time of his arrest.

The California Emergency Medical Services registry shows a man named Richard Paul Stephenson had his EMT license suspended in 2010. That suspension was to be lifted in 2020.

The investigation by Martinez police and an internal investigation is ongoing, Con Fire said.

Stephenson has been employed with the county for 19 years.