Optimum sustainable groundwater management requires the collection of detailed hydrogeological parameters. One of the most important parameters is the recharge rate, which can be challenging to determine by conventional methods. Various methods have been utilised to study groundwater recharge mechanisms for several decades including environmental and artificial tracer techniques. In more recent years, contaminated sites investigations requiring the analysis of Per- and Poly Fluoroalkyl Substances (PFAS) in groundwaters have led to a large number of data sets available in aquifer systems. This provides an opportunity to assess its value in estimating recent recharge and recharge rates that can be important input values for modelling and managing the groundwater system.
The premise for determine recharge rates from PFAS concentration is that PFAS can be considered a conservative tracer in groundwater flow in a similar way that chloride or tritium travels through groundwater systems conservatively. Since the time that PFAS enters the groundwater system is known from historical records, the maximum depth and distance that PFAS travels in the groundwater system can provide a good estimate of the travel time and therefore provides a recharge rate for that system.
Publicly available data sets were utilised in this preliminary assessment of PFAS as a novel approach to recharge estimation. Investigation sites with water quality data that included PFAS measurements and key hydrogeological data such as bore lithology, SWL, multiple screen-depths, and other aquifer properties were collected and analysed. The assessment utilised data from sites that had the most detailed hydrogeological information and examined minimum data requirements.
The results from this initial assessment indicate that providing that a site investigation has a well-planned and detailed monitoring network, PFAS can be used to quantify recharge rates in a groundwater system. Given that there are many water quality/contamination studies across a range of aquifer systems requiring the measurement of PFAS, this data can be utilised not only for determining if a site exceeds health and environmental criteria, but can be used to provide valuable model input data and sustainable groundwater management for regulators in the future.