(1) Except as provided in WAC 173-408-080, the methane concentration limits set forth in subsection (2) of this section apply to a MSW landfill subject to this chapter beginning on whichever of the following dates is later:

(a) January 1, 2025;

(b) Upon commencing operation of a newly installed gas collection and control system or modification of an existing gas collection and control system pursuant to WAC 173-408-080; or

(c) A date established by the department to accommodate significant technological improvements, which may include the installation of an energy recovery device or devices, which does not exceed 24 months after the department adopts rules to implement this chapter.

(2) No location on a MSW landfill surface may exceed the following methane concentration limits, dependent upon whether the owner or operator of the MSW landfill conducts instantaneous surface emissions monitoring or integrated surface emissions monitoring in accordance with WAC 173-408-110(1):

(a) Five hundred parts per million by volume, other than when measured by nonrepeatable, momentary readings, as determined by instantaneous surface emissions monitoring; or

(b) An average methane concentration limit of 25 parts per million by volume as determined by integrated surface emissions monitoring.

(3) Any reading exceeding the applicable limit set forth in subsection (2) of this section must be recorded as an exceedance and the following actions must be taken:

(a) The owner or operator must record the date, location, and value of each exceedance, along with retest dates and results. The location of each exceedance must be clearly marked and identified on a topographic map, at a minimum, of the MSW landfill, drawn to scale, with the location of both the monitoring grids and the gas collection system clearly identified;

(b) The owner or operator must take corrective action, which may include, but not be limited to, maintenance or repair of the cover, and well vacuum adjustments. The location or locations of any exceedance must be remonitored within 10 calendar days of a measured exceedance; and

(c) The owner or operator must notify the department or local authority in accordance with WAC 173-408-110 (1)(b).

(4) The requirements of this section do not apply to the following areas, provided that the owner or operator ensures these areas are no larger in size and no longer in duration than is necessary for the specified activity:

(a) The "working face" of the landfill, as defined in WAC 173-408-020;

(b) Areas of the landfill surface where the landfill cover material has been removed for the purpose of installing, expanding, replacing, or repairing components of the landfill cover system, the landfill gas collection and control system, the leachate collection and removal system, or a landfill gas condensate collection and removal system;

(c) Areas of the landfill in which the owner or operator, or a designee, which is a person or entity that has express, written permission from the owner or operator, is engaged in active mining for minerals or metals; or

(d) Areas of the landfill surface where the landfill cover material has been removed for law enforcement activities requiring excavation.