40 CFR § 281.42 - Requirements for public participation.
(a) Authority that allows intervention analogous to Federal Rule 24(a)(2) from Title IV of the Federal Rules of Civil Procedure, and assurance by the state that it will not oppose intervention under the state analogue to Rule 24(a)(2) on the ground that the applicant's interest is adequately represented by the state.
(b) Authority that allows intervention of right in any civil action to obtain the remedies specified in § 281.41 by any citizen having an interest that is or may be adversely affected; or
(c) Assurance by the appropriate state agency that:
(1) It will provide notice and opportunity for public comment on all proposed settlements of civil enforcement actions (except where immediate action is necessary to adequately protect human health and the environment);
(2) It will investigate and provide responses to citizen complaints about violations; and
(3) It will not oppose citizen intervention when permissive intervention is allowed by statute, rule, or regulation.