Unlike foundation pads, landfills are not stable ground. They are masses of decomposing organic material and shifting moisture — the exact type of terrain where slope failures occur. The biogas industry must treat this terrain as a geotechnical hazard before building long-term energy infrastructure.

The Overlooked Overlap Between Biogas Infrastructure and Unstable Ground

The extent of overlap between biogas infrastructure and unstable ground is greater than many outside the waste sector realize. As of late 2024, roughly 488 municipal solid waste landfills across the United States were feeding landfill gas to active energy projects, with hundreds more identified by federal regulators as candidates for future gas-to-energy development.

Biogas is produced through a process known as anaerobic digestion, which effectively breaks down organic components into fuel.

All those sites share the same underlying condition — the gas being harvested is a direct by-product of the same decomposition process that destabilizes the waste mass over time. Wells, pipelines, compressor stations and flares are typically installed directly into or immediately adjacent to the slope itself, which means the infrastructure generating the renewable energy is physically anchored to the ground most likely to move.

Landfill Slopes Behave Nothing Like Natural or Engineered Soil

Engineers who work with natural slopes or compacted earthen embankments are used to predictable material behavior. Municipal solid waste does not offer that predictability. As a heterogeneous mix of organic and inorganic material, it decomposes and generates gas and liquid after placement. This means its density changes throughout the site’s life.

A review of landfill instability cases spanning 22 counties over four decades identified high leachate levels, poor compaction, weak foundation soil and low interface strength between the waste and the liner system as recurring causes. It also found that the sudden release of built-up landfill gas is a contributing factor in several documented failures.

The combination of a biologically active fill material, an engineered liner system with its own strength limits and gas pressure building somewhere inside the mass gives landfill slopes a failure profile that doesn’t map cleanly onto standard geotechnical design assumptions.

Leachate Buildup and the Physics of a Weakening Slope

Leachate, the liquid that percolates through decomposing waste, is one of the clearest drivers of slope instability. As leachate accumulates faster than a site’s collection system can remove it, pore water pressure rises within the waste mass, effectively reducing the friction that holds the slope together.

A stability analysis based on actual landfill failure surfaces found that raising the water level within a 20-meter slope by just 1.5 meters reduced the safety factor by 0.1, illustrating how sensitive these slopes are to leachate accumulation or heavy rainfall events over relatively short periods. For a biogas operation, this creates an uncomfortable overlap of incentives.

The same organic breakdown that produces marketable methane also produces the leachate that erodes the slope’s structural margin, and slowing one process to protect stability can mean slowing the other process that makes the site profitable to operate.

When Landfill Slopes Fail, the Consequences Go Beyond Just Waste

A comparative study of five MSW landfill slope failures found that, under standard static loading conditions, the calculated safety factors at each site fell below the minimum reliability index and failure probability thresholds. Also, under U.S. Army Corps of Engineers classifications, all five slopes were rated hazardous under seismic loading.

Failures at this scale can bring physical harm to workers and residents and create serious environmental risks. Energy infrastructure sitting on these slopes inherits that same exposure, especially because geohazards can affect critical infrastructure sectors, including power, pipeline, water, transportation and communication systems.

A pipeline corridor or compressor station damaged by slope movement results in lost energy production and a safety incident at a site that regulators and nearby communities were told was being managed responsibly.

Monitoring and Mitigation Are Catching Up, But Adoption Lags Behind Buildout

The tools to manage risk continue to improve. Geotechnical sensors such as inclinometers, piezometers and ground-penetrating radar can detect early shifts in waste mass position and slope movement well before they become visible failures. Combining this kind of instrumentation with modern data analytics allows operators to predict long-term settlement trends rather than reacting to them after the fact.

The gap is also about how consistently the technology is deployed. Instrumentation adds cost to a project, and biogas economics are sensitive enough that stability monitoring can end up treated as optional rather than standard, particularly at older or smaller sites converted to energy production well after the original landfill design was finalized.

Landfill gas systems have viability as long-term infrastructure rather than temporary add-ons. They often require extended operating windows and recurring maintenance access as the waste mass settles beneath them. Treating slope behavior as an energy-project variable helps operators protect renewable output while supporting safer long-term performance across the full project life cycle.

Treating Ground Stability as Part of the Energy Equation

Biogas from landfills displaces methane that would otherwise escape into the atmosphere, and that environmental case is not in dispute. What deserves more attention is the ground beneath the equipment. Bringing the same rigor to slope stability that the industry already applies to gas capture efficiency is not a constraint on biogas growth. It is what makes that growth durable enough to trust. Stronger geotechnical planning will help ensure landfill biogas remains a resilient renewable energy strategy as deployment expands.

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