What steps can owners and operators of coal-fired power stations take now to ease the passage to closure and leave a positive legacy? In this series of articles, we’ll explore some of the key considerations, such as managing ash dams and demolition waste, remediating sites for safety and stability, and working with stakeholders and communities to identify new opportunities and maximize value.
Part 1: Managing waste
Although there is plenty of public awareness and concern about the waste streams of coal-fired power stations during operation (particularly carbon emissions), less attention is given to the waste implications of closure. How can the ash dams be managed and made safe for the long term? When the cooling towers and power station structures come down, what will be done with the solid waste left behind?
For owners and operators of coal-fired power stations, waste management during operation, decommissioning, demolition and post-closure is complex and can be challenging. There are, however, pathways towards achieving sustainable solutions at manageable cost to the business and minimal cost to the environment and communities. With good closure practices, industrial sites that are a liability to owners can even be transformed into assets for industrial, residential or recreational land uses.
Risks and opportunities of ash dams
During power station operation, ash is produced as a byproduct of coal combustion. In Australia, coal ash is estimated to make up one-fifth of the nation’s total waste stream. The huge volumes of ash are usually slurried and placed in impoundments (dams) or dewatered and deposited in dry-stacks. Such facilities require maintenance and monitoring to confirm their structural integrity. Following closure, ash impoundments and dry-stacks must be capped and rehabilitated to minimize their environmental impact and meet regulatory requirements.
The greatest risks involved in managing ash dams are the potential for catastrophic failure (as occurred in 2008 at the Kingston Fossil Plant in Tennessee) and the potential for leakage or seepage of heavy metals, salinity and toxic substances into surface water or groundwater.
The design of older ash dams may not have included liners or systems to collect and control seepage. These environmental and stability risks must be considered carefully in the closure design. Developing a robust remediation and monitoring plan is critical to regulatory success and social license. The risks and opportunities will be better understood if specialist advice is sought on the ground conditions and implications for the site. This will be the key to finding a balanced approach that neither underestimates nor overestimates risk, and achieves a safe, suitable result without excess cost.
To manage ash dams for the long term, more options are available than closing the dams on site. For example, some of the ash can be reused in the production of cement, construction blocks or bricks. However, in many cases reuse isn’t possible or feasible and capping the ash dam on site may be the most economical and sustainable option.
Significant savings can be achieved through smart containment design that is informed by a detailed understanding of the ground conditions and an appreciation of envisaged future uses for the site. Due to the age of Australia’s coal-fired power stations, most ash dams are unlikely to have been designed with long-term future land use in mind. This is why closure planning should define potential future land uses as early as possible, to guide an appropriate capping design and rehabilitation plan.
The closure of ash dams is constrained by physical and chemical stability risks. However, it is important that the rehabilitated dam does not limit the potential future land uses. In many cases, the most likely outcome is encapsulating the ash and preserving it as a resource for future or progressive use whilst managing risk.
Options for ash management after closure should be driven by the site’s constraints and opportunities, including regulatory drivers, community needs, environmental considerations and engineering aspects. These options need to be assessed strategically to progress the best option for all stakeholders.
Dealing with demolition waste and contamination
Following closure of a power station, demolition waste becomes a major management challenge and a very significant expense. Asbestos and other hazardous materials are likely to be present at power station sites and will need special attention and careful handling.
There is an alternative to trucking all of this material away from the site for disposal in other landfills and waste management facilities. It is worth considering whether the asbestos waste or other solid waste materials can be encapsulated within the ash dam/landfill, which can then be capped with overburden from the mine operation. This approach has the potential to save millions of dollars in landfill fees, avoid consuming scarce and valuable landfill space, and avoid vast numbers of truck movements, with their associated emissions, fuel use, noise pollution and road safety impacts.
As asbestos waste can range from soft materials to hard waste (such as demolition rubble, pipes, metal sheeting), bridging or access layers will be needed in the containment design so that more waste can be placed in the future. It’s also important that heavy machinery access is considered if solid waste is going to be placed into the ash dam.
Although on-site disposal of asbestos and solid wastes could be a sustainable and cost-effective solution to a waste problem, it’s essential to gain the support of the regulator and the community for such an approach. Building trust requires full transparency and a well justified design.
It’s never too early to plan for closure
In Australia, it is still early days in what will be a progressive closure of coal power stations around the country. At this stage, there’s little local precedent, a high level of governance risk, and the potential for onerous conditions from regulators. Although we are all learning together, the time to plan for closure and waste management is here.
Whether closure is on the immediate horizon, or is still some way off, owners and operators of coal-fired power plants should move quickly to develop best-practice rehabilitation and closure plans, informed by a range of reliable specialist expertise, and developed in consultation with affected communities. This is the path to gaining the confidence of regulators and stakeholders, and leaving a safe and stable legacy.
About the author
Daniel Dohle is a Principal Engineer at Golder, a member of WSP, based in Melbourne, Australia. He has over seventeen years’ experience in containment design, including landfills, smelter waste containment cells, ash dams and mine waste. Daniel uses a ‘cradle-to-grave’ approach in his designs as he is experienced in design, tender, construction, operational inspections, closure design and aftercare of containment and waste storage facilities.
