There's a bit of difference between mass surveillance and the infrastructure necessary for a viable chemical weapons program. Assuming a major nation state woul

There's a bit of difference between mass surveillance and the infrastructure necessary for a viable chemical weapons program. Assuming a major nation state would even want to, considering their rather limited tactical value on the modern battlefield. Anyhow, the Organization for the Prohibition of Chemical Weapons out of The Hague oversees compliance with the Chemical Weapons Convention. That includes verifying the destruction of stockpiles and weapons facilities as well as industry inspections that closely monitor precursors, as well as investigating cases of alleged production or usage. As of last October, 93% of declared stockpiles has been destroyed and independently verified by the OPCW. You don't have to take the US government's word for their numbers.