Sydney's Groundwater Researched

Deep water: a new technology probes Sydney’s groundwater for the first time

Groundwater is an essential resource that provides drinking water to billions of people around the world. Here in Australia – the driest inhabited continent in the world – water is a particularly precious resource that we need to manage carefully.

Yet mining and other subsurface engineering projects have the potential to impact groundwater. In the Sydney Basin region, underground coal mines operate near surface water reservoirs that are important for Sydney’s water supply. In other regions, coal seam gas extraction is being managed to minimise risk to adjacent aquifers.

Some mines also operate deep below wetlands and sensitive ecosystems. In other areas, copper, gold and coal mines are going deeper underground, and we have limited knowledge of how they will interact with groundwater.

So it is essential that we improve our knowledge of how ground water connects with surface water and aquifers, which is precisely what we’re doing at the Connected Waters Initiative Research Centre (CWI) at UNSW.

Laser sniffer

The best tracer of groundwater is the water itself. In our recent study, we measured the different isotopes within water found in the rock. This can tell us about surface water-groundwater interactions in the past, and provides an essential baseline for any future changes.

To gather the samples, we had to drill 300 metres through layers of sandstone, siltstone and claystone to extract a core. This core then had to be carefully packed and sealed to preserve the moisture held in the rock.

Back in the laboratory, we had to carefully prepare bags with moist rock samples and dry air. We then used a specialised laser technology, called Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) to “sniff” the air in the bag to determine its composition. It uses a system of mirrors to measure the amount of laser energy absorbed by water molecules of different mass, and can pick out different water isotopes.

We used this new technology to measure for the first time the water in rock pores of the strata in the Sydney Basin. We compared its isotope composition to known natural tracer composition in rainfall, surface water and other known water sources.

This allowed us to work out where the water came from. We also identified four distinctive layers of rock, or hydrogeological zones, which control groundwater movement in the Sydney Basin.

Before we conducted our research, we simply didn’t know much about the deep groundwater system in Sydney Basin. With our new record, this means that if some future mining project impacts the groundwater, we can now use this pore water isotope records as a novel baseline to help determine the extent of the impact.

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Taxonomy

• Research
• Groundwater
• Water Management