In 1994, up to 225 tons of a sticky substance called Catacarb spewed into the air and on property in Crockett and Rodeo from the former Unocal refinery.
The Contra Costa Times reports that 6,000 people got sick and the refinery agreed to a $80 million settlement.
The chemical release also formed a first-of-a-kind pollution monitoring system that detects slow toxic leaks. But residents say the refinery's current owner, Conoco-Phillips, has allowed that system to fall into disrepair. The hearings will conclude sometime next month.