Waiwera is a small coastal village located on New Zealand's North Island above a geothermal reservoir. The origin of the warm water is not well understood. An inferred fault zone at the base of the reservoir is thought to channelise the uprising thermal water. The observed characteristic cold and hot water distribution in the system was simulated and the temperature profiles show an improved agreement in the near field around the centre of the reservoir.

Uranium migration for a close to real case situation is quantified with reactive transport simulations using input data from the deep geothermal borehole Schlattingen, which is near the targeted area in Switzerland, and including the effect of the multi-barrier system on the source term. The hydrogeological system must always be considered in safety assessments since adjacent aquifers have a major impact on the pore water geochemistry, and hence sorption processes.

Migration of uranium in the potential host rock Opalinus Clay is used as an example to demonstrate the extent to which simulated migration lengths can vary for a million years, depending on the model concept and on the underlying data and parameters. To reduce the uncertainty in this context, the calcite carbonate ion and the hydrogeological system at a potential disposal site need to be known, whereas the quantity of clay minerals plays a subordinate role, as long as it is enough.

The Repository Site Selection Act explicitly emphasises that targeting the disposal of high-level radioactive waste is a so-called learning process. We are of the opinion that the procedure and the available data should be combined with geoscientific knowledge to support the identification of siting regions. We propose this workshop and invite all experts who have dealt with the search for a repository site from a geoscientific perspective.

The present study, uses density-driven flow and transport models to evaluate mechanisms of saline water intrusion from deep aquifers into the freshwater column used for drinking water supply under different boundary conditions and for a specific site in the German Federal State of Brandenburg. Results show that mainly decreasing groundwater recharge leads to increased and earlier salinisation which highlights the need for waterworks to initiate effective countermeasures quickly and in time.

The geothermal hot water reservoir below the small town of Waiwera in New Zealand has been known to the indigenous Maori for many centuries. Overproduction by European immigrants led to a water level decrease and consequently artesian flow from the wells and the seeps on the beach ceased. The Te Kaunihera o Tāmaki Makaurau Auckland Council established the Waiwera Thermal Groundwater Allocation and Management Plan to allow the geothermal system to recover.

The TRANSPORT Simulation Environment (TRANSPORTSE) was coupled with the geochemical reaction module PHREEQC, providing multiple new features that make it applicable to complex reactive transport problems in various geoscientific fields. Two computationally demanding and complex geochemical benchmarks were used in the present study to successfully verify the code implementation.

Safety assessments must demonstrate that radionuclides in potential disposal sites are retained within the containment providing rock zone using reactive transport simulations. Here, this is quantified for the example of uranium in the hydrogeological system of the Opalinus Clay at Mont Terri. Our work clearly shows how sensitive migration lengths resulting from simulations are to the model conceptualisation and selection of underlying data.

Porosity-permeability relations are simulated for a precipitation-dissolution cycle in a virtual sandstone. A hysteresis in permeability is observed depending on the geochemical process and dominating reaction regime, whereby permeability varies by more than two orders of magnitude. Controlling parameters for this hysteresis phenomenon are the closure and re-opening of micro-scale flow channels, derived from changes in pore throat diameter and connectivity of the pore network.

POET is a parallel reactive transport simulator which implements a mechanism to store and reuse previous results of geochemical simulations through distributed hash tables. POET parallelizes chemistry using a master/worker design with noncontiguous grid partitions to maximize its efficiency and load balance on shared-memory machines and compute clusters.

The geothermal reservoir at Waiwera has been subject to active exploitation for a long time. However, the continuous production of geothermal water, to supply hotels and spas, had a negative impact on the reservoir. The aim of this work was to link the influence of the abstraction rates to the measured water level data to derive reservoir properties. For the analysis, a modified deconvolution algorithm was implemented and shown to be applicable and in accordance to results of a pumping test.

The present contribution provides an overview on the collaborative project iCROSS and reports selected results. The impact of considering complex coupled processes in repository subsystems for the assessment of the integrity of a given (generic) repository arrangement will be discussed. The interdisciplinary team combines experimental work in the lab, in the underground rock laboratory and environmental simulations in order to achieve process understanding across variable scales.

Uranium migration in the Swiss Opalinus Clay is used as an example to quantify the influence of varying values of a stability constant in the underlying thermodynamic database within the law of mass action on the migration lengths. The difference of the stability constant of 1.33 log units lead to changed migration lengths of 5 m to 7 m. With a maximum diffusion distance of 22 m the influence of an uncertain stability constant is negligible for the host rock scale.

Barite formation is an important factor for many use cases of the geological subsurface because it may change the rock. In this modelling study, the replacement reaction of celestite to barite is investigated. The steps that were identified to play a role are celestite dissolution followed by two-step precipitation of barite: spontaneous formation of small crystals and their subsequent growth. Explicitly including the processes improve the usability of the models for quantified prediction.

DecTree evaluates a hierarchical coupling method for reactive transport simulations in which pre-trained surrogate models are used to speed up the geochemical subprocess, and equation-based full-physics simulations are called only if the surrogate predictions are implausible. Furthermore, we devise and evaluate a decision tree surrogate approach designed to inject domain knowledge of the surrogate by defining engineered features based on law of mass action or stoichiometric reaction equations.

Utilization of geothermal reservoirs as alternative energy source is becoming increasingly important worldwide. Here, we studied the surface expression of a warm water reservoir in Waiwera, New Zealand, that has been known for many centuries but remained little explored. Using thermal infrared cameras we were able to show renewed activity of the hot springs on the beachfront and identified faults and fractures as important fluid pathways, as well as individual fluid conducting lithologies.

Energy supply in Germany is subject to a profound change. The present paper addresses the German potential of storing excess energy from renewable power sources in the geological subsurface. Wind and solar electricity can be transformed into hydrogen, and with carbon dioxide subsequently into methane. The current potential for combined subsurface storage of methane and carbon dioxide allows to store far more than required to date and is estimated to provide the entire coverage in 2050.