Montana Code Annotated
Part 5. Montana Underground Storage Tank Act
75-11-508. Corrective action -- petroleum mixing zones

75-11-508. Corrective action -- petroleum mixing zones. (1) A corrective action plan prepared pursuant to 75-11-309 may include the use of a petroleum mixing zone, as defined in 75-11-503, in conjunction with the final remediation and resolution of a petroleum release.
(2) If a petroleum mixing zone is included in a corrective action plan, it may be established only when:
(a) all source material has been removed to the maximum extent practicable;
(b) the extent of petroleum contamination has been defined;
(c) natural breakdown or attenuation is occurring within the plume; and
(d) no further corrective action is reasonably required at the site.
(3) The boundary of a petroleum mixing zone established in accordance with this section must be contained within the boundary of the property on which the petroleum release originated unless a recorded easement, a restrictive covenant, or another institutional control approved by the department on an adjoining property allows the petroleum mixing zone to extend onto the adjoining property.
(4) Monitoring of a petroleum mixing zone may not be required unless there is a unique, overriding, site-specific, impact-related reason to require monitoring.
(5) At the downgradient boundary of a petroleum mixing zone, the concentration of any petroleum constituent, including benzene, may not exceed a water quality standard adopted pursuant to 75-5-301.
(6) If a petroleum mixing zone is established and maintained:
(a) the petroleum release is considered resolved;
(b) no further corrective action for the petroleum release is required; and
(c) the department shall issue a no-further-action letter to the owner or operator stating that a petroleum mixing zone has been established for the release and describing any conditions required to maintain the petroleum mixing zone.
(7) A corrective action plan approved by the department pursuant to 75-11-309 may be amended to include a petroleum mixing zone in accordance with this section, including a corrective action plan approved prior to April 15, 2011.
History: En. Sec. 5, Ch. 189, L. 2011; amd. Sec. 2, Ch. 107, L. 2015; amd. Sec. 69, Ch. 324, L. 2021.