Enforcement Alert: EPA Finds MSW Landfills are Violating Landfill Gas Emission Rate Calculation Requirements

MSW Landfill Operators Fail to Include Wastes from Total Degradable Waste-in-Place and Properly Sample Landfill Gas, Resulting in Underreported Emissions

This Enforcement Alert is intended to remind municipal solid waste (MSW) landfill operators and owners, and their consultants, of the importance of properly identifying and documenting nondegradable wastes excluded in calculations and collecting representative landfill gas (LFG) samples for non-methane organic compounds (also referred to as “NMOC”) analysis and emission calculations. 

Understanding these concepts is important for purposes of correctly calculating landfill NMOC emissions and determining applicability of requirements to install and operate a gas collection and control system (also referred to as “GCCS”) to ensure compliance with MSW landfill regulations.  

The U.S. Environmental Protection Agency (EPA) has found Clean Air Act compliance issues at MSW landfills prompting the Agency’s concern with the uncontrolled release of LFG. Based on the results of recent investigations and enforcement actions, the EPA:  

  • Found significant issues related to landfill gas emission rate calculations where many landfill operators are improperly excluding wastes from total degradable waste-in-place, and 

  • Observed that many operators are improperly collecting LFG samples for NMOC analysis and emission rate calculations for determining regulatory applicability for GCCS requirements. 

MSW landfill gas is comprised of roughly 50% carbon dioxide and 50% methane gases by volume. Methane is a super climate pollutant and is a greenhouse gas more than 28 times more potent than carbon dioxide in trapping heat in the atmosphere. The gas is flammable and explosive if not properly managed. Other trace gaseous constituents include NMOC, which include volatile organic compounds (VOC) and hazardous air pollutants (HAP), as well as sulfur-based compounds, all of which can contribute to air quality issues and public health concerns.  

Methane and VOC contribute to ground-level ozone formation, and VOC emissions are a precursor to fine particulate matter formation. Ground-level ozone, particulate matter, sulfur gases, and HAP emissions are associated with premature mortality, respiratory distress, irritation, asthma, nausea, and cancer, among other issues. NMOC and sulfur gases contribute to odors and quality of life issues for surrounding communities. 

The EPA is issuing two enforcement alerts on MSW landfills at the same time. The other alert  addresses violations of the requirement to conduct adequate monitoring techniques and system maintenance at MSW landfills to ensure compliance with the Clean Air Act.  Enforcement Alert: EPA Finds MSW Landfills are Violating Monitoring and Maintenance Requirements is available on the Agency’s website.

On this page:

I. Regulation of MSW Landfills

MSW landfills are regulated under several federal environmental laws and regulatory programs. This Enforcement Alert focuses on MSW landfills that may be subject to a combination of the following standards under the Clean Air Act:  

These regulations require MSW landfills with a design capacity of 2.5 million megagrams (Mg) of waste mass and 2.5 million cubic meters of waste volume or greater, to calculate the NMOC emission rate for the landfill using procedures specified in the regulations to determine if they are subject to GCCS requirements. The calculation must include the waste in all cells of the landfill, including cells that contain construction and demolition waste. MSW landfill operators need to correctly calculate this value to accurately assess applicability to requirements to control emissions. 

Calculating an NMOC emission rate involves inputting waste acceptance history into the decay equation described in the regulations. This is typically calculated using the EPA’s Landfill Gas Emissions Model (LandGEM). The regulations provide tiered options for determining landfill-specific variables that landfills must input in the decay equation: 

  • Tier 1: Default values 

    • NMOC concentration = 4,000 ppmv (as hexane); 

    • k (methane generation rate constant) = 0.05 per year (or 0.02 per year if average precipitation is less than 25 inches per year). 

  • Tier 2: Site-specific NMOC concentration based on landfill gas sampling and analysis via EPA Method 25C (detailed below). 

  • Tier 3: Site-specific NMOC concentration from Tier 2 along with site-specific methane generation rate constant (k) determined by EPA Method 2E. 

The MSW regulations also allow landfills with calculated emissions between 34 and 50 Mg to opt to conduct Tier 4 surface monitoring. However, this option is rarely used. Use of alternative methods from the above requires site-specific EPA approval, per the regulations.  

When inputting the waste acceptance history, a MSW landfill operator may exclude nondegradable waste per the regulations if appropriate documentation is maintained on all excluded wastes and is readily accessible. 

Per 40 CFR part 60, subparts Cf and XXX, all MSW landfills with annual NMOC emission rates calculated at or above 34 Mg must submit a GCCS design plan within 12 months, install and operate a GCCS, and comply with all monitoring and record-keeping requirements within 30 months after the first NMOC report shows that the landfill is above the threshold.  

In the design plan, landfill owner/operators should include the calculations for the maximum expected gas generation rate for the purpose of sizing and designing the GCCS to be compliant with regulatory requirements. This calculation uses a similar decay equation to the NMOC calculation and typically is calculated using LandGEM. 

Note: The Greenhouse Gas Reporting Program requirements under 40 C.F.R. part 98, subpart HH use a different decay equation and utilize different input categories for waste types and constants than the equations under the NSPS, EG, and NESHAP for MSW landfills.

II.  Findings from EPA Investigation at Municipal Solid Waste Landfills

In the EPA’s investigations of MSW landfills, the EPA found that many landfill operators are not properly determining and documenting nondegradable wastes, nor properly sampling LFG for the NMOC concentration, to determine a site-specific NMOC emission rate per NSPS, EG, and NESHAP requirements. This can result in violations for delayed or avoided installation of a GCCS and failure to follow regulatory monitoring and reporting requirements. 

A.  Documenting Nondegradable Wastes

Nondegradable wastes may be excluded from the total mass of waste-in-place used in NMOC emission rate calculations. Clean Air Act regulations define nondegradable wastes as “[A]ny waste that does not decompose through chemical breakdown or microbiological activity”. (40 C.F.R. part 60, subpart XXX and 40 C.F.R. part 63, subpart AAAA) 

The regulatory definition highlights that examples of nondegradable wastes include, but are not limited to, concrete, municipal waste combustor ash, and metals.  

Wastes containing organic materials or any other materials that may break down are degradable and will lead to LFG emissions. Subpart XXX requires that these wastes be included in all NMOC emission modeling or calculations. Examples include household waste, auto-shredder residuals (also referred to as “ASR” or “fluff”), wastewater treatment sludges, petroleum contaminated soils, and alternative daily cover that includes degradable waste.  Federal regulations require owners/operators to include alternative daily cover (that includes degradable waste) in NMOC emission modeling, even if the applicable state agency does not require this waste amount to be included and reported as waste deposited in a landfill.  

When investigating MSW landfills’ NMOC emission rate calculations, the EPA observed that some owners/operators incorrectly classified waste streams as nondegradable. For example, construction and demolition (C&D) debris, which often contains nondegradable materials, such as concrete, also contains degradable materials, such as wood and gypsum wallboard. Nondegradable C&D can be excluded only if the landfill is specifically tracking and keeping records of the excluded loads, including both the waste type and the amount excluded. Some industrial solid wastes resulting from manufacturing processes may be nondegradable; however, if an MSW landfill excludes such industrial wastes, it must keep records of the waste type and amounts excluded. 

To subtract nondegradable waste from NMOC modeling or calculations, the landfill operator must maintain documentation of the nature and amount of such wastes. (See 40 C.F.R. § 60.764(a)(1)(i)(B)) Landfill operators should maintain proper protocols for documenting such information and communicate these requirements to landfill staff to ensure consistency. 

The exact categories and descriptions of waste types may vary by state. Many categories for solid waste reporting under state requirements may provide insufficient information to establish whether the waste is nondegradable. In NMOC reports, owners and operators should include detailed records of the types of wastes and tonnages excluded as nondegradable. If a design plan submission is required under the regulations, landfill owners/operators must obtain agency approval to exclude any waste stream in the maximum expected gas generation calculation or make any other modifications to the equation or constants. 

B.  LFG Sampling for Site-Specific NMOC Analysis

Figure 1. LFG probe sampling.
Figure 1.  LFG probe sampling.

The regulations provide that owner/operators may measure site-specific NMOC concentrations for a MSW landfill using a Tier 2 test, which involves collecting LFG samples and analyzing them using EPA Method 25C. LFG samples collected for NMOC analysis should be representative of the MSW landfill and/or landfill areas in question to give an accurate site-specific concentration. Protocols for Tier 2 testing are specified in 40 C.F.R. §§ 60.764(a)(3) (NSPS), 60.35f(a)(3) (EG), and 63.1959(a)(3) (NESHAP).

Although Method 18 was previously allowed under 40 C.F.R. part 60, subpart WWW, current regulations no longer allow its use.

For MSW landfills without an active GCCS, landfill owner and operators should take representative LFG samples using the driven probe method as described in the Tier 2 protocols using two sample probes per hectare with a 50-sample requirement for sites greater than 25 hectares. (See Figure 1.) Gas collection points within the passive collection system may also be used for sample collection if they meet the above requirement.

LFG Sample Location Prior to Gas Treatment

For MSW landfill sites with an active GCCS, landfill owner and operators should take representative LFG samples using the system as described in the Tier 2 protocols in accordance with the following regulatory requirements: 

  • The well field is representative and meets the two sample probes per hectare requirement; 

  • Samples are collected from an appropriate header pipe location within the GCCS (e.g., common header pipe representative of all gas in GCCS); 

  • Sampling is performed prior to any gas moving, condensate removal, or treatment system equipment (see Figure 2); and 

  • A minimum of three LFG samples are collected from the header pipe. 

III.  Municipal Solid Waste Landfill Enforcement Action Example

Through its investigations, the EPA has found noncompliance with waste characterization and LFG sampling requirements at MSW landfills nationwide. The Agency has taken numerous enforcement actions against MSW landfill owners and operators for improper calculation of annual NMOC emission rates. By improperly calculating the NMOC emission rate, landfills improperly avoid the GCCS design plan and operation requirements.  

Case examples include: 

  • Niagara Falls Landfill – Niagara Falls, NY (2024): To resolve Allied Waste’s Clean Air Act violations at its Niagara Falls Landfill, which caused excess LFG emissions to be released to the atmosphere, the company agreed to operate a GCCS that is compliant with the Act and pay a $671,000 penalty.  Violations included improper exclusion of areas of gas-generating industrial and C&D wastes and failure to timely install and operate a gas collection and control system on the active and inactive cells of the landfill. 

  • Mill Seat Landfill – Bergen, NY (2023): To resolve Clean Air Act violations at the Mill Seat Landfill, Waste Management of New York and Monroe County in Bergen, New York agreed in a settlement with EPA to pay a penalty, operate a compliant Clean Air Act GCCS, and begin conducting quarterly surface emission monitoring. The violations included failure to maintain adequate documentation of the amount and nature of nondegradable waste that it was receiving and failure to include the landfill’s total mass of solid waste when calculating its NMOC emission rate. Mill Seat Landfill also failed to collect representative LFG samples for its Tier 2 testing. 

IV. Resources

Helpful resources to assist owners and operators with information to achieve compliance are available on the following EPA web pages and sites:

Disclaimer:  This Enforcement Alert addresses select provision of EPA regulatory requirements using plain language.  Nothing in this Enforcement Alert is meant to replace or revise any Clean Air Act permit, any EPA regulatory provision, or any other part of the Code of Federal Regulations, the Federal Register, or the Clean Air Act.

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Last updated on September 27, 2024