This is how laws work in the US though, it’s called rule making authority. For example, the clean air act doesn’t specify any of the levels or pollutants, it empowers (or in that case creates) the Department or Agency to make rules within some often quite broad guidelines. That agency will then conduct research, hold public meetings that nobody goes to, and then make rules which are enforced under the law.

Edit: those laws sometimes get amended by congress and sometimes extended or have their enforcement deprioritized by the executive.