Early Career Hydrogeologists’ Network Technical Meetings

August 2023 Event – Christchurch

The next ECHN: Ōtautahi branch event #3 is Wednesday 30th August 2023, 5:30 to 6:30 pm.

Held at WSP office, 12 Moorhouse Ave, Ōtautahi/Christchurch, 8013

Access: The WSP office is at 12 Moorhouse Avenue, Addington, Christchurch, and can be accessed through the main entrance at that address.

Socialising with drinks & nibbles will be available between 5:30 pm and 5.45 pm.

For catering purposes, please RSVP by 28 August 2023 to iahnz.earlycareer@gmail.com

Title: Aquifer Test Interpretation in Real World Aquifers

Presenter 1 : Ryan Burgess (Hydro Geochem Group)

Background: Ryan is a Senior Hydrogeologist with over 12 years’ consulting experience, focusing on groundwater management. He has undertaken various roles, from project manager to technical specialist, on multidisciplinary teams responsible for the exploration, development, and management of groundwater resources across New Zealand, Australia, and North and South America.

He advises on multiple aspects of groundwater studies, including exploration, resource development and wellfield design, hydrogeological characterization, source water protection (i.e., capture zones), construction dewatering, numerical modelling, groundwater-surface water interactions, and assessment of environmental effects. Ryan has extensive experience involving both granular and fractured bedrock aquifer settings, ranging across shallow unconfined aquifers with connection to surface water to deep confined sedimentary basins.

Presentation: The interpretation of aquifer tests including a single observation well are routinely straightforward and a single estimate of aquifer properties is obtained. In the case where multiple observation wells are monitored during an aquifer test, the exercise becomes much more challenging. Groundwater level responses are typically variable, reflecting the heterogeneous nature of the aquifer. Estimates of aquifer properties from separate analyses at individual wells often produce inconsistent results. When one recalls that a key underlying assumption of most analytical solutions is that of homogeneity, the only conclusive finding is that the conceptual model upon which the analyses is based is violated, possibly severely so. When analyses are approached in this way, none of the estimates may be reliable.

In this presentation, an alternative approach will be suggested. The tools are not new. In fact, they represent the simpler of the tools we already have at our disposal. Rather, it’s the application of critical thinking that empowers the analyst. The advocated approach may allow an analyst to see the forest from the trees, and estimate the representative average transmissivity of real, that is heterogenous, aquifers.

Title: An introduction to PFAS and their subsurface fate and transport

Presenter 2: Matt Silver (Environment Canterbury)

Background:  Matt is an environmental geochemist with experience in academic, consulting and governmental roles. Prior to joining Environment Canterbury in May 2023, he worked as a PFAS/emerging contaminants specialist at the Wisconsin Department of Natural Resources (Wisconsin, USA). Matt did his doctoral degree in Germany on the fate of pharmaceutical and nitrogen compounds during infiltration of treated wastewater, within an EU project on Managed Aquifer Recharge. While at the Wisconsin Department of Natural Resources, Matt led a study collecting water samples from 450 private wells across the state to determine PFAS prevalence and infer source types affecting groundwater away from known PFAS point sources.

Presentation: Per- and polyfluoroalkyl substances (PFAS) are a large group of human-made chemicals that were first used in products in the 1950s. Since then, PFAS have been put into increasing numbers of products over time and today can be found as water-repellent and grease-resistant coatings in items including food packaging, carpeting and upholstery, clothing, furniture and cookware. While those uses all represent possible dispersed sources of PFAS to groundwater, some PFAS uses at industrial facilities and their presence in certain types of firefighting foams can result in major point source releases to groundwater. PFAS are often present in products in formulations that can degrade to release perfluoroalkyl acids (such as PFOA, PFOS and PFHxS, for which New Zealand has recently enacted Maximum Acceptable Values for drinking water). The PFAS formulations in products do not necessarily contain perfluoroalkyl acids directly, rather “precursor” compounds, which pose a challenge to mass balance approaches and can represent long-term sources to groundwater. If released, several factors can lead to PFAS accumulating in soil or moving slowly through vadose zone material above the water table. Once in groundwater, PFAS tend to behave more similarly to other contaminants (such as nitrate) and do not degrade.