Landfill Design and Management
Building Value for the Landfill Gas Stream
Increasingly, given concerns about energy shortages and global climate change will drive considerations more towards landfill gas capture. Landfills that are already designed and operated with landfill gas capture in mind will have an advantage in this new area of competition.
Dyfed Evans, Dr. Robert Gregory and Simon Copping
With much of the world’s waste management strategy still focused on landfills, the recovery of landfill gas for use as an energy source has become a significant business, where either renewable energy or greenhouse gas drivers exist. Accordingly, it seems likely that landfill gas capture considerations will become more dominant in design of landfills.
In the UK, the landfill gas business is predominantly owned and operated as an enterprise separate from the waste disposal and landfill management operation. This means that many of the lessons learned in the UK for integrating waste management and landfill gas operations concurrently have application elsewhere in the world. Some of these lessons have come through work undertaken to analyze recoverable landfill gas energy potential, for purposes of setting a financial value on that potential.
Gas Capture Factors
The amount of gas—primarily methane—that can be expected to be captured from a landfill depends on several factors, including:
How tightly the landfill is sealed against leakage of methane through the base, sides or top of the waste mass.
How quickly the landfill has been filled. Over time, the methane-generating capacity of waste declines, and so, if the cell is filled slowly, its methane potential may have mostly dissipated by the time the gas collection system is installed.
In existing landfills that are being retrofitted for gas capture, the age of the landfill and the type of waste are major determining factors in the amount of gas that can be captured.
Depth of the waste. Methane can be more easily captured if the waste mass is deeper, wet but not waterlogged, and with a small surface area, compared to a wider, shallower waste mass that is poorly drained.
One of the biggest factors in methane capture has to do with the nature of the waste stream itself. Construction waste tends to produce little methane compared with much of the municipal or commercial waste stream.
Faster Attenuation
As waste management practices shift more towards diversion of organics into separate treatment streams, there is a reduction in the methane producing capability of the remaining stream. As a result, the revenue producing capacity of landfills is becoming attenuated. This means that instead of being described by gas generation curves with exponential post closure tails showing revenue possibilities two or three decades into the future, the declining portion of the curve may be steeper, illustrating faster attenuation.
Hot Spots
One of the considerations to be made in valuing landfill gas streams is the potential cost of not managing landfill gas production adequately, seen as increased potential for offsite gas migration, odor and, in extreme cases, the potential for fire. Deep-seated hot spots, sometimes referred to as landfill fires, can develop due to particular types of waste or by the ingress of air into the waste mass leading to heating and smoldering of the waste mass in situ. Once established, these hot spots become difficult to extinguish.
Collecting and Managing the Gas
Another factor to consider is the cost of collecting and managing the gas. Collection can be done through a sacrificial-pipe system, in which horizontal perforated pipe is laid at various levels throughout the landfill as it is filled, connected to a collection network. A more robust system, installed after a waste cell has been filled, comprises a network of vertical pipes installed through the landfill in an optimal pattern to collect the landfill gas.
All of these financial considerations are largely dependent on the incentives available to help them along. The UK’s financial credits (ROCs) for generating energy from renewable sources and other programs such as the Clean Development Mechanism, permit options that may not at present be financially available in certain jurisdictions such as much of the U.S., where there are currently fewer financial supports available.
The Valuation Process
Where the fiscal and regulatory environment makes landfill gas to energy practical, the valuation process contains three steps:
The valuation of the resource—determining the volume of the landfill, the nature of the waste in it including how much organic waste there is, whether the landfill is capped or if rainfall is able to percolate through it, moisture content and other factors, which determine the landfill gas potential. In addition, the records of the landfill operator are examined to see what waste has been deposited, and in which parts of the landfill. From this, a prediction can be made for the amount of gas available for power generation.
Examine any gas collection infrastructure on site, together with the technology used to convert the gas to energy—from gas field collection efficiency to the electrical efficiency of the plant, other loss factors, the level of maintenance, and any investment required to bring the operation to a suitable level of effectiveness.
Determine the operation’s level of environmental compliance, as well as find out if any capital investment needs to be made to maintain compliance.
Financial advisors are then able to use this information to set a monetary value on the business, using numbers that are based on the best available science.
In landfill design and management, many of the parameters are already set—the nature of the waste, the size and shape of the landfill, and other factors. This means that many aspects of the landfill are pre-determined. However, there are still many factors that can be decided by the operator, and many of these decisions can make it easier or more difficult to collect the methane produced by the landfill.
Increasingly, given concerns about energy shortages and global climate change—including the need to reduce methane, a powerful greenhouse gas—will drive considerations more towards landfill gas capture. Landfills that are already designed and operated with landfill gas capture in mind will have an advantage in this new area of competition.
Dyfed Evans is a Principal of the Leeds, UK office of Golder Associates. He has 18 years of experience as a consultant, working on land impact and due diligence projects. He has managed such projects across a number of industrial sectors including waste management, oil and gas, chemical, electronics, manufacturing, specialty chemicals, paper-pulp, mining, electronics and automotive industries. He has also undertaken the design of numerous characterization and remediation projects for the redevelopment of contaminated and industrial sites. Dyfed is a Principal of Golder Associates.
He can be reached at 44 (0) 1937 837 800 or via e-mail at [email protected].
Dr. Robert Gregory is a Principal in the company’s Nottingham, UK office. He has an international reputation within the industry and his career has included landfill site auditing, permitting, landfill gas resource assessment and environmental compliance. For the regulator, he has delivered applied research in support of evidence-based regulatory guidance, drafting of regulatory guidance documents, training on waste management and landfill gas modeling, including producing the GasSim landfill gas model. In 2006 he served as Review Editor of the Waste Management Chapter in the Mitigation Volume of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report into Climate Change. This report was instrumental in the IPCC being jointly awarded (with Al Gore) the Nobel Peace Prize 2007. He can be reached at 44 (0) 115 937 1111 or via e-mail at [email protected].
Simon Copping is a Principal in Golder’s Maidenhead, UK office and is UK and Eire Business Development Leader. He is a Senior Engineering Geologist with more than 20 years of experience working in the UK and abroad on a range of waste management and mining projects. Simon has a broad engineering background, having led the design, development, construction and project management of a range of waste handling, processing, treatment and disposal facilities. Simon has also provided commercial, technical and environmental due diligence support to a number of waste management company acquisitions in particular the modeling and mapping of theoretical to actual gas generation and recovery values for renewable energy portfolio assessments. He can be reached at 44 (0) 1628 586 200 or via e-mail at [email protected].