Which of the following is NOT considered an enforcement action?

A cease and desist order is a legal directive requiring a person or entity to stop engaging in certain behaviors, typically to prevent further harm or violations of the law. While it is an authoritative action that can have significant consequences, it is fundamentally aimed at preventing ongoing non-compliance rather than imposing penalties or sanctions after a violation has occurred, which characterizes typical enforcement actions.

In contrast, the other choices involve formal penalties or significant regulatory actions taken to rectify or punish non-compliance with environmental laws. For instance, an administrative civil penalty imposes a financial charge for violations, suspension of county registration typically restricts a person's or business's ability to operate legally until compliance is achieved or demonstrated, and revocation of a restricted materials permit removes the legal allowance to use certain materials, thus enforcing compliance with pre-established regulations.

The selection of cease and desist order as not being an enforcement action reflects the understanding that while it is a powerful regulatory tool, it primarily serves to halt activities rather than to penalize past infractions, distinguishing it from the other more punitive enforcement measures listed.