So, you're entering into the nexus of contract space, engineering ethics, and permitting.
If your contract says that you will provide a tank that meets California laws, then you probably need to figure out what will meet legal requirements for your customer. Did they at least specific a...
Agreed, I would ask your customer to flow down some requirements for you.
-What code is the system designed to?
-Do the tank drawings/calculations require a professional engineer (PE) stamp? Does that person have to be licensed in california?
-Is this a nuclear plant? If so, does it need an...
I know this is beyond the scope of your original question - but are you exactly being asked to do?
If you're just trying to learn more about CA laws/codes, ignore this. Otherwise, you will want to review specifically the set of requirements that you're being asked to work to in your procurement...