Protecting groundwater from mining and industrial waste

With 97% of the world’s fresh water coming from groundwater, it’s an asset worth protecting. However, our habit of burying domestic and industrial waste as landfill and storing mining waste above ground is a threat to this precious resource.

As rainwater filters through this waste, it leaches acids, heavy metals and toxic chemicals, which drain into the aquifer below. Once it’s been polluted, groundwater can be expensive and difficult to clean up.

One way to minimise contamination is to cover waste with store-release covers - a layer of soil, trees and plants. The soil soaks up the rainwater, which can then be used by the vegetation rather than travelling down through the stored waste.

While this works well, it can be expensive and slow to implement. A team at the National Centre for Groundwater Research and Training (NCGRT), led by Professor Derek Eamus, has developed a cheaper and more efficient way to test the optimal design of these store-release covers.

“To build a cover, we have to know what type of soil and plants to use, and how thick the soil layer should be,” said Professor Eamus.

“Also, every site has a different climate, vegetation and soil, so a lot of it is guesswork, followed by hundreds of experiments. It can take years and years to optimise the design of a store-release cover.”

To solve this problem, the researchers ran a soil-plant-atmosphere model with different climate scenarios to test its effectiveness in designing store-release covers. To find out which covers work best, they looked at four factors: the depth of the soil layer, how much water it can hold, how much water a plant will use and the local rainfall.

They then applied the model to three different Australian climates: cool, wet winters with hot, dry summers in Perth; the monsoonal climate in Darwin; and evenly distributed rainfall across the year such as in Sydney.

“We found that an effective store-release cover has to have enough capacity to store any additional rain that falls in wetter years. The trees have to grow leaves that cover the entire ground, and their roots have to reach the bottom of the soil cover,” Professor Eamus said.

“Now we know what makes an effective store-release cover, we can gather the information for these factors, as well as the rainfall average and extremes for any location, to optimise the design of a store-release cover anywhere in the world.”

Professor Eamus says he hopes the research will encourage mining and waste management companies to invest in building better waste covers and will help tackle the problem of groundwater pollution globally.

The NCGRT research was recently published in the journal Hydrological Processes. The study is available here.