When used in this chapter, the following terms have the meanings given below. These definitions should not be interpreted to apply to any other chapter unless expressly provided for therein.

"Active mining" means actively excavating a landfill or a portion thereof using conventional mining technology to recover and reuse minerals and/or metals until such a time that the landfill cover is replaced.

"Active municipal solid waste (MSW) landfill" means a municipal solid waste landfill that has accepted or is accepting solid waste for disposal and has not been closed in accordance with the requirements set forth in WAC 173-351-500 as it existed on January 10, 2022.

"Air contaminant" has the same meaning as set forth in WAC 173-400-030.

"Air pollution" is presence in the outdoor atmosphere of one or more air contaminants in sufficient quantities and of such characteristics and duration as is, or is likely to be, injurious to human health, plant or animal life, or property, or which unreasonably interfere with enjoyment of life and property. For the purpose of this chapter, air pollution does not include air contaminants emitted in compliance with chapter  17.21 RCW.

"Ambient air" means the surrounding outside air.

"Authority" or "local authority" means any air pollution control agency whose jurisdictional boundaries are coextensive with the boundaries of one or more counties.

"CERCLA regulated landfill" means the portion of a municipal solid waste landfill that has been designated as on-site for purposes of a CERCLA response action(s).

"CERCLA response action" means a removal or remedial action conducted pursuant to 42 U.S.C. Sections 9604, 9606, 9620, 9621, or 9622.

"Closed municipal solid waste landfill" means a municipal solid waste landfill that is no longer accepting solid waste for disposal and has been closed in accordance with the requirements set forth in WAC 173-351-500 as it existed on January 10, 2022.

"Component" means any equipment that is part of a gas collection and control system and that contains landfill gas including, but not limited to, wells, pipes, flanges, fittings, valves, flame arrestors, knock-out drums, sampling ports, blowers, compressors, or connectors.

"Component leak" means the concentration of methane measured one half of an inch or less from a component source that exceeds 500 parts per million by volume (ppmv), other than "nonrepeatable, momentary readings," as defined in this section. Measurements from any vault must be taken within three inches above the surface of the vault exposed to the ambient air.

"Continuous operation" means that a gas collection and control system is operated continuously, the existing gas collection wells are operating under vacuum while maintaining landfill gas flow, and the collected landfill gas is processed by a gas control system 24 hours per day.

"Department" means the department of ecology.

"Destruction efficiency" means a measure of the ability of a gas control device to combust, transform, or otherwise prevent emissions of methane into the ambient air.

"Emission" means a release of air contaminants into the ambient air.

"Enclosed combustor" means an enclosed firebox which maintains a relatively constant limited peak temperature generally using a limited supply of combustion air. An enclosed flare is considered an enclosed combustor.

"Energy recovery device" means any combustion device that uses landfill gas to recover energy in the form of steam or electricity including, but not limited to, gas turbines, internal combustion engines, boilers, and boiler-to-steam turbine systems.

"Exceedance" means the concentration of methane measured within three inches above the landfill surface that exceeds 500 ppmv, other than "nonrepeatable, momentary readings," as defined in this section, as determined by instantaneous surface emissions monitoring; or the average methane concentration measurements that exceed 25 ppmv, as determined by integrated surface emissions monitoring.

"Gas collection system" means any portion of a gas collection and control system that employs various gas collection wells and connected piping, and mechanical blowers, fans, pumps, or compressors to create a pressure gradient, actively extract landfill gas, and convey the gas to the gas control system.

"Gas control device" means any device used to dispose of or treat collected landfill gas including, but not limited to, enclosed flares, internal combustion engines, boilers and boiler-to-steam turbine systems, fuel cells, and gas turbines. A gas control device is a component used in a gas control system.

"Gas control system" means any portion of a gas collection and control system that disposes of or treats collected landfill gas by one or more of the following means: Combustion; gas treatment for subsequent sale, or sale for processing offsite, including for transportation fuel and injection into a natural gas pipeline.

"Hazardous waste" has the same meaning as set forth in RCW 70A.300.010.

"Heat input capacity (HIC)" means the hourly heat content available on a steady state basis in the form of landfill gas generated from a landfill's waste source material.

"Hydrocarbon detector" means an instrument used for the measurement of methane that meets the calibration, specifications, and performance criteria of EPA Reference Method 21, Determination of Volatile Organic Compound Leaks, 40 C.F.R. Part 60, Appendix A (in effect on the date in WAC 173-400-025).

"Inactive municipal solid waste landfill" means a municipal solid waste landfill that is no longer accepting solid waste for disposal and has been closed in accordance with the requirements set forth in chapter 173-304 WAC. For purposes of this rule, an inactive municipal solid waste landfill is subject to all requirements applicable to an active municipal solid waste landfill unless and until (a) the department or local authority determines the landfill is exempt in accordance with WAC 173-408-070 (4)(b)(ii); or (b) the owner or operator submits a closure notification in accordance with WAC 173-408-170(8).

"Increased meter reading" means a single or series of meter reading(s) above 200 ppm of methane.

"Inert waste or nondecomposable waste(s)" has the same meaning as "inert waste" in WAC 173-350-100.

"Landfill" has the same meaning as set forth in RCW 70A.205.015.

"Landfill gas" means any raw gas derived through a natural process from the decomposition of organic waste deposited in a MSW landfill, from the evolution of volatile species in the waste, or from chemical reactions of substances in the waste.

"Landfill surface" means the area of the landfill under which decomposable solid waste has been placed, excluding the working face.

"Limited purpose landfill" has the same meaning as set forth in WAC 173-350-100.

"Municipal solid waste (MSW)" means a subset of solid waste which includes unsegregated garbage, refuse and similar solid waste material discarded from residential, commercial, institutional, and industrial sources and community activities, including residue after recyclables have been separated. Solid waste that has been segregated by source and characteristic may qualify for management as a non-MSW solid waste, at a facility designed and operated to address the waste's characteristics and potential environmental impacts. The term MSW does not include:

(a) "Dangerous wastes," as defined in RCW 70A.300.010, other than wastes expressly excluded from the requirements of chapter 173-303 WAC, Dangerous waste regulations, as set forth in WAC 173-303-071, such as household hazardous wastes;

(b) Any solid waste, including contaminated soil and debris, generated by a "CERCLA response action," as defined in this section, or by a remedial action taken under the Model Toxics Control Act, chapters 70A.305 RCW and 173-340 WAC; nor

(c) Mixed or segregated recyclable material that has been source-separated from garbage, refuse and similar solid waste. However, the residual from source separated recyclables is MSW.

"Municipal solid waste landfill" means a discrete area of land or an excavation that receives municipal solid waste, including household waste, and that is not a land application site, surface impoundment, injection well, or pile.

"Nonrepeatable, momentary readings" means indications of the presence of methane, which persist for less than five seconds and do not recur when the sampling probe of a portable gas detector is placed in the same location.

"Nozzle offset distance" means the horizontal distance between the "unmanned aerial system," as defined in this section, and the distal end of the nozzle when flown as a fixed above ground level (AGL) and a known nozzle tube length.

"On-site" has the same meaning as set forth in 40 C.F.R. 300.400(e)(1) (in effect on the date in WAC 173-400-025).

"Operator" means any "person," as defined in this section, that:

(a) Operates a MSW landfill;

(b) Is responsible for complying with any federal, state, or local requirements relating to methane emissions from a source located on real property used for MSW landfill purposes and subject to this chapter; or

(c) Operates any stationary equipment for the collection of landfill gas from a MSW landfill subject to this chapter.

"Owner" means any "person," as defined in this section, that:

(a) Holds title to any portion of the real property on which a MSW landfill subject to this chapter is located including, but not limited to, title held by joint tenancy, tenancy in common, community property, life estate, estate for years, lease, sublease, or assignment, except title held solely as security for a debt such as mortgage;

(b) Is responsible for complying with any federal, state, or local requirements relating to methane emissions from a source located on real property used for MSW landfill purposes and subject to this chapter; or

(c) Owns any stationary equipment for the collection of landfill gas from a MSW landfill subject to this chapter.

"Person" means an individual, firm, public or private corporation, association, partnership, political subdivision of the state, municipality, or governmental agency.

"Professional engineer" means an individual who is registered in Washington and holds a valid certificate to practice engineering in Washington as provided under chapter 18.43 RCW.

"Putrescible waste" means solid waste which contains material capable of being readily decomposed by microorganisms and which is likely to produce offensive odors.

"Solid waste" means all putrescible and nonputrescible solid and semisolid wastes including, but not limited to, garbage, rubbish, ashes, industrial wastes, commercial waste, swill, sewage sludge, demolition, and construction wastes, abandoned vehicles or parts thereof, discarded commodities and recyclable materials.

"Third-party owner or operator" means any "person," as defined in this section, that:

(a) Owns any stationary equipment for the collection of landfill gas from a MSW landfill subject to this chapter; or

(b) Purchases or otherwise obtains untreated landfill gas from an owner or operator of a MSW landfill subject to this chapter and owns any stationary equipment for the treatment and/or combustion of the landfill gas.

"Unmanned aerial system (UAS)," commonly known as a drone, means an aircraft without any human pilot, crew, or passengers on board. In this context, a UAS includes multiple rotors such that the minimum speed is not limited by stall and can be reduced all the way to zero (hover).

"Waste in place" means the total amount of solid waste placed in the MSW landfill estimated in tons. The solid waste density is assumed to be 1,300 pounds per cubic yard, and the decomposable fraction is assumed to be 70 percent by weight, unless the department or local authority approves alternative values.

"Working face" means the open area of a MSW landfill where solid waste is deposited daily and compacted with landfill equipment.