Oakley police spotted the chemical, later identified as hypochloride, leaking from one of the hoses underneath the truck at about 2:10 p.m. and pulled the truck over near the intersection of Bridgehead Road and Main Street.
According to Lee, fumes from the chemical entered the police car and a sergeant and one other officer became sick. They were taken to Sutter Delta Hospital in Antioch.
"They were overcome by the fumes; initially we didn't know how much spilled out, but we've determined it's hypochloride solution, which is used in water treatment facilities," Contra Costa County Sheriff's Lieutenant Eric Navarro said.
Only a small amount of the chemical leaked out before the truck driver was able to shut off the leak. The hypochloride solution is about as twice as strong as household bleach.
Initially, sheriffs evacuated a couple nearby businesses and closed a several mile stretch of Main Street, fearing the substance was the much more dangerous hydrochloric acid, but they later determined further evacuations or a shelter-in-place were not necessary.
The driver told ABC7 he was headed from Tracy to Pittsburg to make a delivery.
"Everything was OK for me, because I always go up there all the time," the driver Mr. Silva said. "Everybody does the same thing in the plant. I don't know, maybe he got confused or something." Traffic is moving in the area, except for turns northbound from Main Street onto Bridgehead Road.
Sheriffs are waiting for California Highway Patrol specialists to determine whether the truck is fit to drive.
Bay City News contributed to this story