Md. Code, Env't § 1-303

(a) A criminal prosecution or a suit for a civil penalty by the Department for violation of any provision of this article or any rule, regulation, order, or permit adopted or issued under this article, shall be instituted within 3 years after the date the Department knew or reasonably should have known of the violation. (b) (1) Subject to paragraph (2) of this subsection, an action for an administrative penalty by the Department for violation of any provision of this article or any rule, regulation, order, or permit adopted or issued under this article, shall be instituted within 5 years after the date the Department knew or reasonably should have known of the violation. (2) The statute of limitations for an action for an administrative penalty for an ongoing violation shall be tolled until the action that caused the ongoing violation has ceased. (c) A suit for a civil penalty by a political subdivision for violation of any provision of this article or any rule, regulation, order, or permit adopted or issued under this article, or for a violation under any regulatory program the political subdivision is required to adopt and enforce under the provisions of this article, shall be instituted within 3 years after the date the political subdivision knew or reasonably should have known of the violation.