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Estimating scope 1 emissions from landfill: The benefits and limitations of the NGER Solid Waste Calculator

With landfill emissions often representing the biggest component of local government carbon footprints, more and more councils are seeking a deeper understanding of how waste emissions are generated, calculated, and, potentially, mitigated.

When it comes to quantifying emissions from council-owned landfills, there are two distinct approaches commonly used in Australia. The first method involves the relatively straightforward practice of multiplying the annual weight of disposed waste by an emissions factor, representing the anticipated lifetime emissions from that mass of waste. This approach, while straightforward, simplifies the complex dynamics of emissions from landfill sites. The second, more sophisticated approach, utilises a First Order Decay (FOD) model as contained within the NGER (National Greenhouse and Energy Reporting Scheme) Solid Waste Calculator developed by the Clean Energy Regulator.

In this article, we explore each method in more detail, with a particular focus on supporting a better understanding of the NGER calculator, its methodology, and its advantages over the “simpler” method. We also assess the practical implications and trade-offs of each approach and discuss how these methods can be used together to gain a more comprehensive understanding of landfill emissions and related abatement opportunities.

Overview of landfill waste emissions calculation methods

Landfill emissions are a critical aspect of greenhouse gas inventories, demanding precision in measurement methodologies. Two prominent methodologies, Methane Commitment (MC) and First Order Decay (FOD), stand out in the evaluation.

The MC method, known for its simplicity, estimates emissions based on the quantity of waste disposed in a given year, using factors used to represent the entire lifecycle of emissions expected from a given quantity of waste. While straightforward, it risks overestimating or underestimating actual emissions (primarily methane) in a given year. The National Greenhouse Account (NGA) provides factors consistent with the MC methodology, although includes a range of factors specific to different waste types, offering a more nuanced approach than simply using total waste volumes.

Conversely, the FOD approach, which is the basis of the NGER Solid Waste Calculator, requires historical data, and more accurately represents actual emissions during the inventory year. This approach calculates greenhouse gases actually emitted that year, regardless of when the waste was disposed. FOD models employ specific “k values” which represent the decay constant, that is, the rate at which a substance decomposes over time. This value varies depending on prevailing climatic conditions, with warmer, wetter climates associated with more rapid decay rates than cooler, drier climates. This feature of FOD models contributes a more sophisticated approach to landfill emissions estimation.

About the NGER Solid Waste Calculator

The NGER Solid Waste Calculator is a tool used in Australia as part of the National Greenhouse and Energy Reporting Scheme. The NGER Scheme is a regulatory framework that requires big emitters to report their greenhouse gas emissions, energy production, and consumption data to the Australian Government. The NGER framework can also be adopted voluntarily by organisations seeking a robust methodology for calculating emissions from activities, including waste disposal.

The NGER Solid Waste Calculator is specifically used to estimate and report the emissions associated with waste activities, such as the disposal of waste to landfill, waste recycling, and other waste management processes such as methane flaring. It helps landfill operators to calculate and report the emissions associated with their waste management practices in a robust and standardised way. The calculator is flexible in its input requirements, and default values are able to be overwritten in accordance with NGER guidelines.

The NGER SWC employs a FOD model, considering the gradual accumulation of emissions over a landfill’s lifespan due to microbial activity and organic material decomposition occurring within historic waste deposits. Accordingly, after a landfill closes, the calculator will show a steady decline in annual methane emissions over time, aligning with the reduction and slowed decomposition of organic matter.

The NGER Solid Waste Calculator has the ability to process detailed input data, including historical information on waste tonnages and changes in waste mix, as well as methane volumes captured, flared, and transferred. It categorises waste streams into specific types and composition categories, allowing for more precise calculations.

Ownership and waste processing scenarios

Whichever method is used for calculation, the distinction in waste facility asset ownership is crucial for accurately attributing emissions to specific entities and addressing responsibilities and liabilities. The NGER guidelines outline two ownership scenarios:

  1. The landfill operator owns both the landfill site and treatment facilities for gases
  2. Different entities manage specific aspects of the landfill and its gases.

The first case involves the landfill operator owning both the landfill site and treatment facilities for gases. This includes flaring and energy generation by running gases through a generator. The second case introduces separate entities, with an example scenario provided in which there is a landfill operator owning the site, a gas manager handling flaring and energy generation, and a third entity managing organic waste.

Establishing the correct system boundaries and quantifying waste flows throughout the system serves as the fundamental basis for undertaking subsequent emissions calculations, and errors at this stage can substantially impact the waste calculator and carbon footprint outcomes.

NGER Solid Waste Calculator in action

The NGER Solid Waste Calculator comprises multiple tabs for data inputs. The initial tab includes basic parameters such as facility name, reporting period, and waste management techniques. This tab also requires specification of a climate zone, which can have significant impact on emissions calculations.

Historical data for waste tonnages, methane volumes captured, flared, and transferred are inputted in subsequent tabs. Waste streams, categorised by municipal solid waste, commercial and industrial waste, and construction and demolition waste, are further divided into specific waste types for precise calculations.

The calculator’s structure also involves inputting data for waste streams, homogenous waste types, diversion of waste, and inert waste allocated for construction cover. The output section provides a comprehensive overview of emissions, with the ability to project future scenarios based on changes in methane capture and treatment practices. The calculator offers a nuanced understanding of long-term methane emissions, allowing users to explore various scenarios and their impacts.

Comparing NGER calculator results with simpler methods

Many of our clients are intrigued to know whether the NGER Solid Waste Calculator yields emissions estimates similar to those of the simple factor method. The answer is: “Often, but not always”. For a recent project undertaken for a NSW coastal council, the results from both approaches were remarkably similar, within a few percent. In this case, this parity could be largely attributed to the close alignment of actual percentages for organic matter in municipal solid waste, as identified in real-world waste audits, with the default values provided by the NGER guidelines.

Another important factor affecting similarity of results is whether or not the landfill has been established and operated fairly consistently over several decades. For new landfills, the use of a FOD model in the NGER Solid Waste Calculator may result in comparatively lower estimates of methane generation when contrasted with the simpler method of multiplying the annual weight of disposed waste by fixed emission factors. Therefore, in the early stages of a landfill’s operation, when the decomposition processes are just commencing, the emissions are likely to appear lower than what would be estimated using fixed factors.

As landfills mature, emissions tend to increase and eventually plateau, aligning the NGER calculator results more closely with the single “lifetime factor” dynamics. The tendency towards convergence over time can, however, be affected by any major changes or interruptions to landfill operations over the years.

These issues highlight the importance of understanding the temporal nature of waste emissions and the unique considerations involved in assessing environmental impacts for both new and established landfill sites.

Limitations of the NGER Solid Waste Calculator

While the NGER Solid Waste Calculator employs a FOD model with specific “k” values, it has only a restricted range of climate zones. This approach can be somewhat crude in modifying the emission estimation process, as shifting between climate zones can significantly impact results, even when dealing with landfills located in seemingly similar areas. The limitation becomes apparent when considering distinctions between common climate zones, such as the shift from dry temperate to wet temperate settings, which can lead to a substantial variation in emission estimates. This highlights a potential challenge in accurately capturing the nuanced environmental conditions that influence waste decomposition.

The NGER Solid Waste Calculator is also somewhat limited as a means for measuring and crediting certain waste management initiatives, such as organics diversion, especially in the short term. With its first-order decay model, it will exhibit a lag in responsiveness due to its consideration of cumulative impacts over the entire lifespan of a landfill. The historical deposits and their associated emissions continue to influence the results, potentially masking the immediate effects of recent waste reduction efforts. While the NGER tool provides a comprehensive and nuanced understanding of emissions over time, it will require a longer timeframe to demonstrate the full impact of short-term initiatives.

By contrast, using a lifetime factor makes the emissions results more responsive to short-term initiatives. In scenarios where a council successfully reduces waste deposits by a significant percentage, the immediate impact would be reflected in the carbon accounting using fixed emission factors. This responsiveness allows for a more instantaneous evaluation of the effectiveness of some waste reduction policies and initiatives.

The NGER Solid Waste Calculator’s ability to accommodate detailed inputs can also be a double-edged sword, as its sophistication may create an illusion of greater accuracy. However the tool’s effectiveness heavily relies on the availability and accuracy of detailed data. Without such comprehensive information, the calculator simply resorts to generic assumptions and standard factors, greatly limiting the precision of its results.

The simpler approach, relying on fixed emission factors multiplied by annual waste weights, proves to be equally reasonable in scenarios with limited detailed data. This method, while not as intricate as the NGER Solid Waste Calculator, maintains a pragmatic balance by offering a straightforward and less resource-intensive means of calculation.

The balance between data processing sophistication and practical utility is always a critical consideration in emissions modelling. Ultimately, the utility of the NGER Solid Waste Calculator is maximised when landfill operators  can provide comprehensive, accurate and detailed information.

Potential synergies

Despite their clear differences, the two approaches to quantifying waste emissions can be employed together as complementary tools to provide maximum insight and usefulness in various contexts. Each method has its strengths and weaknesses, and their integration allows for a more comprehensive understanding of landfill emissions.

As mentioned, the simpler approach of relying on lifetime factors is particularly effective in capturing short-term changes and initiatives. It provides quick insights into the immediate impacts of waste reduction measures. On the other hand, the NGER calculator offers a more nuanced, long-term perspective, considering the entire lifecycle of a landfill, and its ongoing impact following closure. Combining the two approaches allows decision-makers to assess both immediate and cumulative effects.

Using both methods also enables validation and comparison of results. By cross-referencing outcomes from the NGER Solid Waste Calculator with those derived from traditional methods, discrepancies or similarities can be identified, investigated, and understood.

In summary, the NGER Solid Waste Calculator is a powerful and useful tool in helping to measure and manage landfill emissions. At the same time, the potential synergies of using multiple calculation methodologies allows for a holistic and adaptable approach to landfill emissions assessment, ensuring that decision-makers have the most useful and insightful information for effective waste management strategies.


If you need help measuring your organisation’s waste-related emissions, or would like support to develop a waste emissions reduction strategy, don’t hesitate to get in touch with us.

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