How is land rehabilitated after mining?

31 March 2022

It’s a long road to rehabilitation — planning for rehabilitation starts before mining activities can even begin, and when mining finishes it’s followed by rehabilitation implementation, monitoring, and maintenance. From beginning to end, the process takes years.

At Stanwell’s Meandu Mine, we undertake progressive rehabilitation: the ongoing, staged restoration of areas disturbed during mining, rather than large-scale works at the end of the project.

Senior Planning Engineer, Steve Jensen, said that rehabilitation was an ongoing process, with several stages.

“Rehabilitation has several key stages — planning, execution, monitoring and maintenance, and ultimately certification,” Steve said.

“Planning for rehabilitation takes place before mining activity begins in a given area, as the final landform needs to be designed before any material is moved to the required location. Each year we identify areas that will be profiled and available for rehabilitation over the following several years.”

With the rehabilitation plan in place, mining activity can begin. Once mining in a specific area of the site is completed and the excavators have left, the disturbed area is assessed, and the earthworks crew gets ready to go to work.

As part of the execution phase, the earthworks crew reprofiles the suitable subsoil material (which was selectively handled and placed during excavation), creating the final profile of the land. This includes establishing contours and drainage systems.

“Our partners, BUMA Australia, have a dedicated earthworks crew on permanent operation who have the tools and expertise we need for most rehabilitation activities,” Steve said.

“Our fleet includes two 657 scrapers used for drainage works and topsoil placement, a water cart, a grader, a D11 production dozer with high precision GPS for final profiling, and a D6 dozer used for seeding, ripping, and the finer earthworks jobs such as drainage works.

“For some specialised works like basalt sorting, haulage, and placement, external contractors are bought in to help out.”

After completing the land profile, and prior to the start of the wetter months, topsoil that’s been kept in a stockpile during mining is brought in and spread with scrapers and small dozers to the appropriate depth.

The next step in the execution of our rehabilitation is ripping, seeding, and enriching the soil. Using small dozers, the soil surface is contour ripped to a depth of 300 – 500 mm. Creating these furrows in the landscape helps to control soil erosion and promotes root penetration and moisture absorption. Seed and fertilisers are applied to the earth using a specially designed seeding unit installed on the D6 dozer.

To date, all rehabilitation at Meandu Mine aimed to return the land to native vegetation. Stanwell uses a rehab seed mix made up of 25 native tree, shrub, and groundcover species, and 10 native grass species. This mix is consistent with the surrounding area, and over time forms a contiguous ecosystem with the surrounding Yarraman State Forest and Tarong National Park.

If everything is done right initially, the next steps are the easiest: rehabilitation monitoring and maintenance. On an annual basis, external consultants come in to monitor rehabilitation — if any maintenance is required, it’s undertaken as part of the annual rehabilitation program and done under the supervision of the Meandu Mine Environmental team. The early remediation of any areas requiring attention, helps to address these items while they are still small and keep the rehabilitation performance on the right trajectory.

After a period of ongoing maintenance, the rehabilitated land is ready for the final stage of the process: certification. Once the monitoring program has provided evidence that the rehabilitation areas meet or exceed the completion criteria, a progressive rehabilitation report is prepared and submitted to the Department of Environment and Science who then make a final decision. In September 2021, Stanwell proudly received official certification of 153 hectares of native vegetation rehabilitation from the Queensland Department of Environment and Science. This is one of the largest ever areas of rehabilitation to be certified in a single application, an area equivalent to nearly 10 times the size of the Brisbane City Botanic Gardens!