Specialist environmental consultancy Umwelt has been involved with several longwall closures over the years, from closure plan development through to sign-off.
Umwelt associate Matthew Newton, who has been with the company for 11 years, said there were a myriad of issues to address when suspending operations. The issues include ground water impacts as a longwall mine that ceases to pump water from underground can potentially cause ground water to build up and affect neighbouring coal mining operations. Impacts do vary from seam to seam though.
“If they stop pumping, in some cases dependent upon the coal seam topography there is potential for fill or spill,” Newton said. “Wherever it spills at surface, there may be particular issues with that ground water quality.”
Ongoing maintenance of pit top facilities, including pollution control systems, is also essential to ensure the site is safe and stable until operations recommence.
To limit potential public liability issues security must be ensured to prevent access to shaft and other mine openings and also to prevent theft and vandalism.
Newton said there can also be public liability consequences for the company arising from interference with access to pit top structures, such as people walking through gantries and other elevated structures.
Legal requirements for a longwall mine on care and maintenance include ongoing compliance with environmental reporting. Statutory conditions also mean keeping positions such as a mine manager, electrical engineer, mechanical engineer and an environmental officer onsite. There are a variety of statutory inspections that also need to be continued throughout the care and maintenance phase.
“While it’s still on care and maintenance you still need to maintain active management systems and ventilation to make sure the mine is liable to be able to start up again,” Newton said.
He added that maintaining the integrity of management systems, such as ventilation and mechanical inspections, can make a longwall mine on care and maintenance a pretty costly exercise.
While care and maintenance aims to keep the mine in a viable or stable condition should operations recommence, closing a longwall mine is a different story.
“This requires detailed investigation to identify the scope of activities required to close the mine to achieve a sustainable post-mining land use,” Newton said.
“What is required to properly seal a mine [includes] detailed rehabilitation plans and associated close-out criteria, demolition plans, environmental controls to be implemented during the closure process, to address issues such as noise generation, water pollution, dust generation, tailings dam capping strategies, hazardous substance handling, the identification and management of potential contamination, social impact strategies, and community and stakeholder consultation strategies.”
A company must also provide sufficient resources and financial backing to keep the site environmentally stable, including keeping experienced operators onsite.
“People who have been on sites for a long period of time, they know where all the potential environmental issues are, which may no longer be obvious. It’s really handy to have them as part of the process so you can actually make sure you address the full scope of closure issues,” Newton said.
“History has shown that not a lot of mining companies have planned well for closure. Some companies have missed out on opportunities to value-add through the closure process so they get a land asset at the end of the process that is sustainable and fit for the intended post-mining land use rather than an ongoing liability.”
Newton argued companies should have a proactive closure planning process that starts in the exploration phase of an operation, through to prefeasibility and the operational phases, with the detail increasing as it approaches closure.
To prepare for worst-case scenarios, Newton also advocated a closure plan should include a contingency for sudden closure.
“It’s not easy to plan for sudden closure, so a closure plan should identify the process you need to go through to identify the risks, to do your detailed site investigations and to update your closure plan accordingly.”
Detailed on-the-ground investigations from a geotechnical, hyrdology and engineering perspective may be necessary to identify the full scope of closure activities.
Newton said under-estimating costs was a huge issue and lack of research could catch a company out if it hadn’t put aside enough money for the work required.
Fumbling a mine closure can trigger various environmental penalties, as well as casting a shadow on the mining industry’s image.
“How well we close a mine is the most important report card for the mining industry, because there’s a lot of derelict sites out there, which unfortunately is how the communities build up their perceptions of mining companies.
“So that’s why it’s critical that companies get the mine closure right so they have more credentials when they go through the process of opening up a new mine. The ability to be able to demonstrate that we can leave a positive legacy for a mine closure is invaluable.”
Newton observed there had been a trend over the past five years for companies to integrate closure planning with day-to-day operations.
Coffey Mining chief executive officer Dan O’Toole said the company had wide-ranging experience in all the different aspects of mine closure. Coffey Mining consultants said technical challenges could include longwall face equipment withdrawal and implementing an operational maintenance program to ensure equipment, such as shields, is not lost or damaged.
According to Coffey Mining, safety precautions for a longwall mine on care and maintenance were not very different to those of an operational mine, but precautions should be tailored to the risk conditions presented. “For instance, greater emphasis would be placed on strata management and control if it is decided to slow down the production rate. Longwalls rely on continuing movement for their security and some system would need to be implemented to ensure they are not adversely affected by weighting problems as well as routine electro-mechanical maintenance issues,” Coffey’s consultants said.
O’Toole said specialists can play an important role in assisting in a longwall mine shutdown.