July 24, 1997 MEMORANDUM TO: RCRA Dockets F-97-FLXF-FFFFF & F-97-FLXP-FFFFF FROM: Allen J. Geswein, Environmental Engineer SUBJECT: Landfill Gas Monitoring Requirements for MSWLFs Under 40 CFR Part 258.23(a) and (b), owners or operators of all municipal solid waste landfill (MSWLF) units must ensure that the concentration of methane gas generated by the facility does not exceed 25 percent of the lower explosive limit for methane in facility structures or that the concentration does not exceed the lower explosive limit for methane at the facility property boundary. To achieve this, "owners and operators of all municipal solid waste MSWLF units must implement a routine methane monitoring program to ensure that [the above standards] are met....The minimum frequency of monitoring shall be quarterly." These requirements were promulgated under the Solid Waste Disposal Facility Criteria Final Rule on October 9, 1991, to protect human health and the environment. The rationale for requiring quarterly monitoring of landfill gas is as follows: HUMAN SAFETY. The decomposition of municipal solid waste produces explosive gases, including methane, carbon dioxide, and hydrogen sulfide. Methane is the constituent of most concern, as it is colorless, odorless, and highly combustible. Migrating methane from MSWLFs has forced the evacuation of nearby residents and businesses and has been responsible for onsite and offsite fires, explosions, property damage, human injury, including asphyxiation, and, in some cases, death (U.S. EPA, 1988a). Sampling air within facility structures where gas can accumulate and sampling soil at the property boundary is necessary to prevent methane buildup. Damage cases have occurred as a result of methane migration from landfills (U.S. EPA, 1988a). Many of these incidents could have been prevented if routine monitoring had been conducted to detect dangerous levels (U.S. EPA, 1988a). Early warning allows the owner or operator to take action to prevent catastrophic events. ENVIRONMENTAL PROTECTION. Migrating methane from MSWLFs has caused ground-water contamination and vegetative destruction on site and on adjacent lands (U.S. EPA, 1988a). Early detection allows owners and operators to take appropriate remedial measures to prevent or minimize environmental damage from migrating gases. EFFECTIVENESS AND RELIABILITY. EPA has established a quarterly gas monitoring frequency as a minimum. Quarterly monitoring will detect gas migration patterns due to seasonal variations and changes in landfill conditions such as partial or complete capping, landfill expansion, gas migration control system operation or failure, construction of new or replacement structures, and landscaping or land use practices (U.S. EPA, 1988b). Resources Used: U.S. EPA. 1988a. Draft background document; operating criteria (Subpart C); "Criteria for municipal solid waste landfills." Washington, DC. July. U.S. EPA. 1988b. 40 CFR Parts 257 and 258, Solid Waste Disposal Facility Criteria; Proposed Rule. 53 Federal Register 33314. Washington, DC. August 30. U.S. EPA. 1991. 40 CFR Parts 257 and 258, Solid Waste Disposal Facility Criteria; Final Rule. 56 Federal Register 50978. Washington, DC. October 9. U.S. EPA. 1993. Solid waste disposal facility criteria: technical manual. Washington, DC. November. U.S. EPA. 1994. Seminar publication: Design, operation, and closure of municipal solid waste landfills. Washington, DC. September.