Extensive usage of vital freshwater is highly undesirable in the current era of climate change and population growth. However, the 6 millionm3/y of brackish seepage that occurs in the deep Horstermeer Polder, located in between the cities of Amsterdam and Hilversumin the Netherlands, is mitigated by using up to 207 millionm3/y of freshwater. This is very unsustainable, especially since the
pressure on the freshwater reserves in the Netherlands is rising. Therefore, this research focuses on evaluating a new mitigation measure of the brackish
upconing below the polder: the extraction of brackish water. In March 2021 AD, a pilot well has been installed in the polder, and its effects were assessed in this research. To enable the evaluation, an extensive analysis of all available measurements of the geology, hydraulic head, and chloride distribution in the area was performed, and a 3D regional variable-density groundwater model using MODFLOW 6 was built. The model result has a reasonable good agreement with these measurements, since at 70% of the measurement locations, the simulated hydraulic head deviates less than 30 cm, and at 80% of them, the simulated chloride concentration deviates less than 200 mg/l. Moreover, compared to previous research, the representation of the brackish upconing was significantly improved. The effects of the pilot well were calculated using five different operational settings. The results indicated that a shallow well, starting below -50 m NAP, reduces the chloride load in the polder more than a deep well (-100 m NAP). However, even in the best scenario, i.e. an active shallow well with a constant pumping rate of 100 m3/h, the reduction of the chloride load is limited to 5.5%. In perspective, these results suggested that at least 24 of these wells are needed to lower the chloride concentration in the discharge water out of the polder to 250 mg/l. On the contrary, the shallow wells cause a considerable average drawdown of 4 cm at surface level in a radius of 50 meters around the well, which might result in damage to wooden pile foundations in the northeast of the polder.

The transition to renewable energy has lead to many new ways of energy production, such as wind and solar energy. For solar energy power, there is an excess of energy during summer and an deficiency of it during winter, which is reversed for the energy consumption. In order to amend this problem, there is an introduction of new ways of energy storage in the form of heat for domestic and industrial use. One of these is the use of Underground Thermal Energy Storage (UTES). These systems make use of the underground to store heat during summer and extract heat during winter by using a fluid as the heat transferring agent. There are many different ways of UTES installation, however there are two which are widely used in the Netherlands: 1) Aquifer Thermal Energy Storage (open systems) which are based on heat-transfer by convection and 2) Borehole Heat Exchangers (closed systems) which are based on heat-transfer by conduction. While the way of transferring heat differs, they both need vertically drilled boreholes to reach a certain storage depth. These boreholes are drilled close to, or underneath, pile-founded buildings. The drilling of boreholes influence in-situ soil stresses around them, which might influence the bearing capacity of the piles. The aim of this thesis is to investigate the influence of installing UTES systems on the bearing capacity of piles. This is done by: 1) investigating the stress changes in sand due to the drilling of boreholes (stress analysis) and 2) the influence of these stress changes on the bearing capacity of piles (bearing capacity analysis). All of the modelling was done in PLAXIS, by using the 2D-axisymmetric model for the first part and the 3D plane strain model for the second part. An advanced soil model for sand was used, with soil mechanical behavior according to the Hardening Soil small strain model. The stress analysis consists out of a parameter sensitivity analysis, including the key parameters: back-fill grout shrinkage and expansion, Over-Consolidation Ratio and Relative Density. After this, the influence of the borehole fluid pressure and borehole diameter on the stress states were investigated. As not all boreholes are drilled perfectly, the last part of the stress-analysis takes into account drilling complications. The bearing capacity analysis includes simulations of static pile load tests of non-displacement piles. Load-displacements curves are produced for several scenario's: 1) perfectly drilled boreholes, 2) boreholes with drilling complications, 3) influence of a soft soil layer and 4) displacement piles and the influence of a varying installation phasing. The results indicate no large effects of perfectly drilled boreholes on bearing capacity of piles located outside a zone of 1.5 times the borehole diameter. For boreholes with drilling complications, the bearing capacity is influenced for piles located in a zone of influence of only several meters (2-6m), depending on the severity of the complication. At last, loaded piles of existing buildings are extremely sensitive for stress changes due to the drilling process, which will cause severe loss of bearing capacity.

Geothermal energy is generally seen as a sustainable source of energy and therefore could be part of the solution for the energy transition. However, there is still a lack of clarity about the conditions under which a geothermal system can be used sustainably. This study investigates the sustainable use of a geothermal system. The geothermal production process in a homogeneous geothermal reservoir with one doublet was simulated using SEAWAT. This model provides the possibility to conduct a sensitivity analysis to examine which parameters play an important role in the geothermal production process. The aim of this analysis was to asses the effect on the well temperature and the thermal recharge, i.e. heat flow from the confining layers towards the reservoir. The tested parameters include four geological uncertainties and two production parameters. From the tested geological uncertainties the thickness of the reservoir has the largest effect on the production profile. Also, it has an impact on the effect of all the other parameters tested, especially on the effect of the confining layers. The confining layers play an important role during the simulation of the production process because they control the thermal recharge, and this enhances the lifetime of the geothermal project. The thinner the reservoir, the larger is the effect of the confining layers and the change in its properties and the more impact the thermal recharge has on the production profile. By examining the effect of the production parameters, the aim was to define a sustainable production design and strategy. It was proven that the production rate has a large impact on the lifetime of a geothermal project, and that an increasing well spacing enhances the sustainable use of a geothermal system. To enhance the sustainable extraction of geothermal energy from a geothermal system the production rate should be kept low. When making a production optimisation two rules of thumb apply to maintain a sustainable production. The first rule says that with a doubling of the reservoir thickness, the production rate can be increased by approximately 50%. The second rule says that with an increase of well spacing of 20%, the production rate can be increased by approximately 50%. Overall, this study emphasizes the positive effect of thermal recharge on the production profile and its enhancement on the sustainable use of a geothermal system. We can conclude that with a sustainable production design and strategy the production from a geothermal system can continue for generations.

High temperature aquifer thermal energy storage (HT-ATES) can potentially solve the mismatch between heat supply and demand. It can provide a large scale seasonal heat storage solution. Thereby it enables an increase in full load hours of the base heat source, which can benefit project performance on both costs and emissions. However, the limited number of successful pilot projects indicates the technology has not escaped its state of infancy. There is a gap from concept to implementation, which is signified by the disagreement of experts on performance drivers and barriers of HT-ATES. This research aims to narrow the described knowledge gap, by improving identification of HT-ATES performance drivers and barriers. Thereby it strives to improve decision making of HT-ATES implementation, and further enhance future HT-ATES application in heating projects. The broad scope of research demands both a diagnostic and design-orientated approach, and fits seamlessly with a multi-criteria decision analysis. The analysis entails the stages of creating, evaluating, comparing and ranking of case-specific scenarios. Parametric variation changes the conditions for HT-ATES implementation across the scenarios. A simulation model is developed and connected to a groundwater model to apply the parametric variation, to create the different scenarios, and consequently to produce the quantitative information for further evaluation. During the stages of creating, evaluating, comparing and ranking, the methodology systematically produces new results on the opportunities and risks introduced by HT-ATES, and additionally on the HT-ATES performance drivers and barriers. The results show that HT-ATES enables the opportunity of improving project performance with respect to the internal rate of return and emissions. Groundwater impact remains the greatest risk, but it can be minimised with smart decision making. To support the decision maker and to overcome the risk of groundwater impact, the research proposes several performance-enhancing, non-explicit guidelines. The guidelines focus on realising an HT-ATES implementation, where project performance with respect to internal rate of return, emissions and groundwater impact are balanced. Thereby they explain the major HT-ATES performance drivers and barriers. The guidelines are summarised below. The decision maker is recommended to .. 1. .. minimise the uncertainty, through thorough subsurface characterization before implementation. Secondly, to focus on aquifers with a minimum depth of 200 [m] and a minimum hydraulic conductivity of 5 [m/d] 2. .. assure network return temperatures during peak demand are below expected storage temperatures 3. .. not consider project life-times exceeding 20 years 4. .. assure yearly maximum base source heat production is always lower than yearly consumer heat demand 5. .. to strive for a flat demand curve and apply peak-shaving, by means of, for example, variable heat prices Currently, the guidelines have the purpose of giving direction to the decision maker, but they will become more explicit once the methodology is improved, and the uncertainty and number of assumptions in the model is decreased.

In a Borehole Thermal Energy Storage (BTES) system, heat is extracted from or injected to the subsurface, taking advantage of the relatively constant temperatures of the underground. Both thermal conduction and advection can influence the performance of BTES systems, but thermal advection is often neglected in the design process. However, in areas with groundwater flow, the heat exchange between the BTES system and the soil can be significantly affected, as the stored heat is transported from the borehole with the flow. This project studies the influence of groundwater flow on the performance of a BTES system. A detailed 3D numerical model is created using MODFLOW and MT3D to simulate groundwater flow and heat transfer under various conditions. The model is verified using an analytical solution as well as experimental data, and is subsequently used to perform a sensitivity analysis and simulate a case study, in order to gain insight on the influence of groundwater flow on the heat exchange process and the conditions that favor this effect. The results reveal that groundwater flow is enhancing the heat exchange rates both in heating and in cooling mode. The magnitude of the effect depends on the total groundwater discharge, and the porosity and background temperature of the soil. In cases of combined heating and cooling, the effect also depends on the magnitude and ratio of the injected and extracted energy loads, as well as the frequency of switching between storage and extraction. Finally, it is revealed that groundwater flow is beneficial for systems with unbalanced energy loads, as it counterbalances the net heat extraction or injection that could decrease the system’s heat exchange capacity in the long term.