Groundwater monitoring is essential for assessing resource availability and conditions, as well as tracking anthropogenic impacts. But, as changing climatic conditions and emerging contaminants place increasing pressure on groundwater, are current monitoring efforts sufficient to manage this crucial resource effectively?
A recent webinar hosted by the National Centre for Groundwater Research and Training (NCGRT) examined groundwater monitoring approaches from different perspectives, including advancements in remote groundwater monitoring, and areas where more could be done.
The Future of Groundwater Monitoring webinar featured insights from University of Newcastle’s Dr Gabriel Rau, as well as CSIRO Research Scientists, Dr Pascal Castellazzi and John Rayner.
NCGRT Director and Flinders University Professor Peter Cook said a lot has changed in groundwater monitoring over the past decades, with changing climatic conditions adding increasing pressures and technology transforming what’s possible.
“There are tens of thousands of monitoring bores across the country, many of which have been monitored for many decades. However, over that time, the threats to groundwater have changed,” Cook said.
“In fact, we could argue that the nature of hydrogeology itself has also changed. We think it is time to ask whether our current monitoring, which focuses mostly on water level and salinity measurement, is sufficient for today’s needs.”
Rayner said there is a huge reliance on groundwater, particularly in Western Australia, and through central Queensland and South Australia.
“One of the interesting areas of work is to use some of the techniques we have to investigate climate change and how that may affect groundwater quality in the future,” he said.
“We know that groundwater quantity and quality are inextricably linked. When we are sampling water, we know that regional groundwater quality changes relatively slowly.
“But the frequency of sampling also depends on the hydraulic parameters that are measured. I am not sure that we have enough hydraulic understanding, and new techniques could potentially be overlaid with our approaches to better target our samples.”
Rayner said there is room for improvement in current practices of groundwater sampling and analysis efforts, particularly in terms of monitoring contaminants.
“Forty years ago, there was a real emphasis on soil physics. This was an area of research that was being investigated to look at groundwater protection,” he said.
“We have now come back to look at soils for characterising contamination before it gets to groundwater, because once a contaminant enters the groundwater system, it's very difficult to remediate or treat, and you may have lost that resource.”
Per- and polyfluoroalkyl substances (PFAS) have come into sharp focus in terms of addressing groundwater protection, Rayner said, and instruments currently being utilised to detect and measure the contaminant movement include lysimeters and tensiometers.
In addition, new sensors are also being developed in an effort to detect PFAS in the unsaturated zone before it enters the groundwater.
“This approach has been used historically to look at nutrient inputs into groundwater, but, in this application, we are trying to see if these sampling devices accessing the soil pore water can be better understood and standardised,” he said.
“There are a lot of guidelines available for sampling groundwater from wells, but there is not the same level of knowledge for collecting samples in the unsaturated zone and how that may relate to impacts on groundwater.
“PFAS is a particularly interesting contaminant, because the majority of it remains in the top couple of metres of the soil profile, even though you may have groundwater contaminant plumes that are tens of kilometres in size.
“Currently we have some ideas, but do not fully understand what’s causing the retention in the vadose zone and the mechanisms underpinning that. This is particularly important. If we are trying to historically model the contribution of a legacy contaminant into groundwater, then we need to know what processes occurred so that we can associate it with things like historical rainfall and evaporation events.”
Another area of research currently being explored includes autonomous sensing, Rayner said.
“CSIRO’s AquaWatch predominantly focuses on surface water systems and the nitrification of water bodies. One of our questions is whether we can do the same type of thing for groundwater,” he said.
“We’ve tried sensing techniques in groundwater over the years and found problems with fouling of sensors and transmission of data. We are not at that level yet, but it's an idea that could be a good supplement to some of the vulnerable areas.”
Rayner said groundwater monitoring and modelling is still developing, with a huge variety of approaches that could be improved or augmented with new technology or approaches.
“There is a lot more uncertainty involved in aspects of temporal and spatial groundwater sample collection compared with laboratory analysis. The variability and uncertainty with collection and preservation of samples is big,” he said.
“We have been using standard wells for a very long time. Could we progress towards instrumenting them or creating smart wells where we have integrated sensors within the well screen itself?”
CSIRO Hydrology and Remote Sensing Research Scientist Dr Pascal Castellazzi specialises in hydrogeodesy, a new research field using satellite-based geodetic observations to understand changes in water availability, distribution and movement.
Satellite data from the GRACE mission – a system of two satellites at about 400kms altitude – has been utilised in recent years to infer groundwater changes in the Great Artesian Basin.
“Hydrogeologists are still somewhat failing at estimating volume changes within aquifers. It’s a difficult thing to do, and, for large aquifers like the Great Artesian Basin, we have numerous influxes in and out that are hard to estimate,” Castellazzi said.
“But satellite systems such as GRACE give us opportunities to assess the changes in groundwater storage through its impact on Earth’s gravity field.”
Castellazzi also said there are ways to monitor ground deformation related to groundwater pressure changes using radar data.
“When we extract water from an aquifer, we create a pressure change. This pressure change, when applied to the compressible sediments within the aquifer, leads to sediment compaction, which induces a change in ground elevation at the surface,” he said.
This technique, referred to as Interferometric Synthetic Aperture Radar, or InSAR, can monitor ground deformation. It was recently applied to assess ground deformation at a managed aquifer recharge (MAR) injunction site north of Perth.
“We start with a ground velocity map of the region before any injection. As we inject, we can see how the ground uplifts. It roughly uplifted by two centimetres there. When we stop injecting, we also see subsidence that corresponds to a ‘back to normal’ movement,” he said.
“We are able to monitor and measure how the ground breathes with our injection phases.
“This is quite concerning because it's an urban area with a lot of infrastructure and networks, we are very interested to make sure that if we do MAR, we are not damaging anything else.”
Geodetic instruments provide independent information and contrast from typical groundwater data and proxies, Castellazzi said, and can unlock new questions around groundwater and help to fill gaps in the science.
“However, we first need to understand the aquifer: a good conceptualisation of the system is essential. Auxiliary data is always required to constrain and interpret,” he said.
“GRACE is an example of this, it is not measuring the same thing depending on where we are looking as it aggregates all water storage changes, which have varying importance depending on climate and lithology,” he said.
Interested in learning more about where groundwater modelling might go in future? Take a look at The Future of Groundwater Modelling webinar here.