Aquifer thermal energy storage (ATES) is a technology with worldwide potential to provide sustainable space heating and cooling using groundwater stored at different temperatures. In areas with high ambient groundwater flow velocity (>25 m/y) thermal energy losses by displacement of groundwater may be prevented by application of multiple doublets. In such configurations two or more warm and two or more cold wells are aligned in the direction of the ambient groundwater flow. By controlling the infiltration and extraction rates of the upstream and downstream wells, the advection by ambient groundwater flow can be compensated by storing thermal energy through the upstream well, while re-extracting it from the downstream well. This study uses analytical and numerical tools and a case study to analyze the relevant processes, and provides guidelines for well placement and an operation strategy for ATES wells in aquifers with considerable groundwater flow. The size of the thermal radius relative to ambient groundwater flow velocity is an important metric. With multiple wells to counteract groundwater flow, this ratio affects the pumping scheme of these wells. The optimal distance between them is around 0.4 times the distance traveled by the groundwater in one year. A larger distance negatively affects the efficiency during the first years of operation.

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A heat pump combined with Aquifer Thermal Energy Storage (ATES) has high potential in efficiently and sustainably providing thermal energy for space heating and cooling. This makes the subsurface, including its groundwater, of crucial importance for primary energy savings. ATES systems are often placed in aquifers in which salinity increases with depth. This is the case in coastal areas where also the demand for ATES application is high due to high degrees of urbanization in those areas. The seasonally alternating extraction and re-injection between ATES wells disturbs the preexisting ambient salinity gradient causing horizontal density gradients, which trigger buoyancy flow, which in turn affects the recovery efficiency of the stored thermal energy. This section uses analytical and numerical methods to understand and explain the impact of buoyancy flow on the efficiency of ATES in such situations, and to quantify the magnitude of this impact relative to other thermal energy losses. The results of this research show that losses due to buoyancy flow may become considerable at (a relatively large) ambient density gradients of over 0.5 kg mg-3m-1 in combination with a vertical hydraulic conductivity of more than 5 m dayg-1. Monowell systems suffer more from buoyancy losses than do doublet systems under similar conditions.@en

Aquifer Thermal Energy Storage (ATES) systems contribute to reducing fossil energy consumption by providing sustainable space heating and cooling for buildings by seasonal storage of heat. ATES is important for the energy transition in many urban areas in North America, Europe and Asia. Despite the modest current ATES adoption level of about 0.2% of all buildings in the Netherlands, ATES subsurface space use has already grown to congestion levels in many Dutch urban areas. This problem is to a large extent caused by the current planning and permitting approach, which uses too spacious safety margins between wells and a 2D rather than 3D perspective. The current methods for permitting and planning of ATES do not lead to optimal use of available subsurface space, and, therefore, prevent realization of the expected contribution of the reduction of greenhouse gas (GHG) emissions by ATES. Optimal use of subsurface space in dense urban settings can be achieved with a coordinated approach towards the planning and operation of ATES systems, so-called ATES planning. This research identifies and elaborates crucial practical steps to achieve optimal use of subsurface space that are currently missing in the planning method. Analysis from existing ATES plans and exploratory modeling, coupling agent-based and groundwater models were used to demonstrate that minimizing GHG emissions requires progressively stricter regulation with intensifying demand for ATES. The simulations also quantified both the thresholds beyond which such stricter rules are needed as well as the effectiveness of different planning strategies, which can now effectively be used for ATES planning in practice. The results provide scientific insight in how technical choices in ATES well design, location and operation affect optimal use of subsurface space, and what trade-offs exist between the energy efficiency of individual systems and the combined reduction of the GHG emissions from a plan area. The presented ATES planning method following from the obtained insights now fosters practical planning and design rules suitable to ensure optimal and sustainable use of subsurface space – that is, maximizing GHG emission reductions by accommodating as many ATES systems as possible in the available aquifer, while maintaining a high efficiency for the individual ATES systems.

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Spatially constant porosity and hydraulic conductivity are usually applied in hydrological studies related to land reclamations. However, the grain sorting and the degree of compaction within land reclamations differ per placement method. A study area at Maasvlakte II, the Netherlands, and the four other land reclamations that could be found in the literature are considered that were constructed by a combination of bottom dumping, rainbowing and discharging the sand-water mixture by pipeline. The structures of the porous media are derived for each placement method and validated by comparison with semi-variograms of cone-penetration tests. It is found that all placement methods lead to some degree of heterogeneity, so that the hydraulic conductivity in these land reclamations is not constant. This is due to the degree of segregation of the grain sizes that differs between placement methods. Segregation even varies within a specific placement method because of its characteristics and site-specific circumstances such as settling depth, grain-size distribution and angularity resulting from grain type. If land reclamations are considered for aquifer storage and recovery for freshwater supply, it should be considered that the recovery efficiency will be affected by both the properties of the material in the borrow area and by the placement methods including their spatial configuration as applied during construction of the reclamation.

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Dune slacks are low-lying, nutrient-poor, species-rich, inter-dunal, seasonally flooded wetlands, are amongst the most threatened habitats in the Dutch coastal dunes. Since 1853 Waternet has been extracting groundwater from the coastal dunes southwest of Haarlem to produce its drinking water. Dune slacks largely disappeared due to the desiccation caused by this water abstraction, over more than a century biodiversity declined as a consequence. Increased societal concern pushed habitat restoration high on the political agenda by the end of the 1980s. It was agreed to do what is possible to restore original dune slacks without endangering the water supply. Far reaching interventions in the dune water system were foreseen to achieve this mutual goal. To allow reliable decision making, the entire hydrological history of the drinking water production in the Amsterdam Dunes since 1853 and its ecological consequences were evaluated over a 10-year study period. The main tool was a 3D groundwater model constructed using all information gathered to date and calibrated using the long-term monitoring data available and widely extended for the purpose, to which ecological modeling was added and calibrated with the available long-term and extended vegetational inventories. These scientific tools were used to assess proposed interventions to be decided upon, which aimed at finding a new balance between groundwater extraction and nature restoration. In 1996 and 2007 large-scale measures were taken, which include filling in of recovery canals, mowing, grazing and sod-cutting to support the native plant communities of wet dune slack habitats. Results of these measures in terms of the restoration of natural hydrological conditions are shown together with the first results for the recovery of wet slacks vegetation that resulted from the combined hydrological and ecological restoration measures that were taken since 1995.

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Regular aquifer storage recovery, ASR, is often not feasible for small-scale storage in brackish or saline aquifers because fresh water floats to the top of the aquifer where it is unrecoverable. Flow barriers that partially penetrate a brackish or saline aquifer prevent a stored volume of fresh water from expanding sideways, thus increasing the recovery efficiency. In this paper, the groundwater flow and mixing is studied during injection, storage, and recovery of fresh water in a brackish or saline aquifer in a flow-tank experiment and by numerical modeling to investigate the effect of density difference, hydraulic conductivity, pumping rate, cyclic operation, and flow barrier settings. Two injection and recovery methods are investigated: constant flux and constant head. Fresh water recovery rates on the order of 65% in the first cycle climbing to as much as 90% in the following cycles were achievable for the studied configurations with constant flux whereas the recovery efficiency was somewhat lower for constant head. The spatial variation in flow velocity over the width of the storage zone influences the recovery efficiency, because it induces leakage of fresh water underneath the barriers during injection and upconing of salt water during recovery.

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