On Dec. 18, 2025, the Colorado Air Quality Control Commission (Commission) adopted new, state-specific rules to regulate methane emissions from municipal solid waste (MSW) landfills. The Commission originally considered Regulation 31 during a two-day hearing in August 2025 and adopted an extensively revised proposal last week. In the months between the Commission’s hearings, several parties participated in numerous, multi-hour work sessions to negotiate changes to the draft rule the Colorado Air Pollution Control Division (Division) proposed.

Colorado’s new Regulation 31 aims to further reduce methane and co-pollutant emissions from MSW landfills by:

  • Setting a lower emissions threshold for gas collection and control system (GCCS) installation and operation than the federal regulations.
  • Imposing aggressive methane monitoring and corrective action requirements, including:
    • 25-foot spacing for quarterly surface emissions monitoring (SEM) or use of an alternative method the Division would approve in the future;
    • A corrective action threshold of 500 ppmv/ppm-m for instantaneous SEM and 25 ppmv/ppm-m for integrated SEM; and
    • Quarterly GCCS inspections.
  • Requiring the use of a biocover or a minimum depth of 18 inches of earthen material for intermediate cover.
  • Prohibiting the use of open flares as a primary or a secondary control device within 1,000 feet of a residential community, mobile home community, daycare facility, school, or hospital located within a disproportionately impacted community after Jan. 1, 2029, unless a narrow exemption applies.
  • Authorizing third-party remote methane monitoring programs to identify emissions from Colorado MSW landfills and empowering the Division to require corrective action for verified emissions.

MSW landfills must obtain Division approval for both existing and new GCCS. In addition to extensive GCCS design standards, the new rule imposes numerous requirements after an MSW landfill shuts down or removes a gas control device due to declining methane levels within the landfill, including the use of biofilters. Regulation 31 also includes extensive state-only recordkeeping and reporting requirements.

Beginning in June 2026, Colorado MSW landfills must annually calculate and report the amount of waste-in-place and the methane generation rate to the Division. Different requirements apply based on the volume of waste-in-place and the methane generation rate. The Division estimates that 32 of the 82 MSW landfills in Colorado, including both open and closed sites, will be subject to the comprehensive Regulation 31 requirements. Colorado’s largest MSW landfills must comply with both the new state and existing federal requirements.

The initial Regulation 31 requirements will take effect on June 30, 2026. However, any MSW landfill a municipal or county government owns with less than eight million short tons of waste-in-place as of Dec. 31, 2025, will automatically receive a three-year extension for most compliance dates.

Regulation 31 joins Colorado’s suite of regulations targeting greenhouse gas emissions with the aim of achieving the state’s goal of 100% net-zero greenhouse gas emissions by 2050. According to Colorado’s Greenhouse Gas Inventory, MSW landfills generated 1.07%  of Colorado’s greenhouse gas emissions in 2020.

Photo of Courtney M. Shephard Courtney M. Shephard

Courtney Shephard guides energy companies through complex regulatory landscapes in the Rocky Mountain West. Her experience spans conventional and low-carbon energy production, with a focus on federal regulatory compliance, permitting strategies, and resolving enforcement matters.

At the core of Courtney’s work is her

…

Courtney Shephard guides energy companies through complex regulatory landscapes in the Rocky Mountain West. Her experience spans conventional and low-carbon energy production, with a focus on federal regulatory compliance, permitting strategies, and resolving enforcement matters.

At the core of Courtney’s work is her comprehensive approach to environmental compliance. She adeptly maneuvers through complex federal mandates—including NEPA, Clean Air Act, and Endangered Species Act requirements—and handles federal administrative appeals. Her experience includes crafting site-specific development strategies for localized development challenges that with the goal of achieving both environmental protection and development objectives.

Leveraging her background in climate policy analysis, carbon market dynamics, and emissions accounting, Courtney collaborates with clients to develop comprehensive carbon management strategies. Her practice includes methane and CO2 reduction strategies, Class VI storage permitting, and pore space acquisitions. She also represents clients in rulemaking and permitting proceedings before the Colorado Energy & Carbon Management Commission.

Access to adequate water supplies is a common project development challenge in the arid western United States. Courtney has more than a decade of experience working with private and municipal clients to appropriate, buy/sell, change, and protect water rights through private transactions and Colorado water court proceedings.

Courtney’s strategic vision and comprehensive understanding of regulatory frameworks have been instrumental in advancing numerous energy and infrastructure projects throughout the region. Her ability to synthesize complex regulatory requirements with practical business needs make her an asset to clients navigating the ever-changing energy landscape.

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Photo of Mary Katherine Andrews Mary Katherine Andrews

Mary Katherine Andrews is a member of the Environmental Practice in Greenberg Traurig’s Denver Office. Her practice focuses on Environmental Litigation and Energy Law, drafting, issuing, and enforcing regulations related to environmental protection.

Mary Katherine advises clients on litigation and enforcement matters, as…

Mary Katherine Andrews is a member of the Environmental Practice in Greenberg Traurig’s Denver Office. Her practice focuses on Environmental Litigation and Energy Law, drafting, issuing, and enforcing regulations related to environmental protection.

Mary Katherine advises clients on litigation and enforcement matters, as well as related auditing and compliance matters, under the Clean Water Act (CWA), Clean Air Act (CAA), Resource Conservation and Recovery Act (RCRA), Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). Mary Katherine is also a member of GT’s Water Law practice, assisting with matters regarding water rights.

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