They don't do chip fabrication there, they make device screens: https://www.siliconvalley.com/2018/03/19/apple-secretly-deve...
> "EPA observed that the sign posted on Solvent Tool 8-113 (B(4)) in Apple’s B(4) Area needs to be updated to remove the chemical “B(4)” from the posted sign, which according to Apple is no longer being used in the facility’s semiconductor process."