Relationship between sedimentary features and permeability at different scales in the Brussels Sands

The Brussels Sands display a complex three-dimensional subsurface architecture. This sedimentological heterogeneity induces a highly heterogeneous spatial distribution of hydrogeological parameters at different scales and may consequently influence subsurface fluid flow and solute migration. This study aims at characterizing spatial variability of permeability at different scales in the Brussels Sands. Firstly, a literature review on the permeability distribution of the Brussels Sands was performed. Secondly, a field campaign was carried out consisting of field observations of the small-scale sedimentary structures and in situ measurements of air permeability. A total of 6550 cm-scale air permeability measurements were carried out in situ in three Brussels Sands quarries in the central part of Belgium: Bierbeek, Mont Saint Guibert and Chaumont Gistoux. On the large basin scale, substantial differences in permeability are observed. A literature data analysis shows that there is no clear correlation between hydraulic conductivity and sedimentary facies. At the small scale, results show that permeability heterogeneity and anisotropy are strongly influenced by sedimentary heterogeneity in all three quarries. Clay-rich sedimentary features such as bottomsets and distinct mud drapes exhibit a different statistical and geostatistical permeability distribution compared to the cross-bedded lithofacies, where the permeability anisotropy is dominated by the foreset lamination orientation

Aquifer Thermal Energy Storage under different hydrochemical and hydrogeological conditions

Energy storage techniques are receiving a growing interest because renewable energy is not always available when needed. One of these energy storage technologies is Aquifer Thermal Energy Storage (ATES). In an ATES system the thermal energy available at the surface is seasonally stored in an aquifer through injection and extraction of groundwater. During summer, cool groundwater is extracted from the cold well(s) for cooling purposes. Through this process the water is heated after which it is injected in the warm well(s). During winter this system is reversed and the stored warm water is extracted for heating purposes. The cooled water is then re-injected into the cold well(s). In this way, warm and cold zones arise around the ATES wells in the subsurface and a seasonal storage of thermal energy is created.The increasing number of ATES systems leads to concerns by drinking water companies and environmental regulators about the long term impacts of ATES systems on groundwater quality. Additionally, only a small part of the subsurface in Flanders meets the optimal conditions for ATES, i.e. the presence of a thick, reasonable homogeneous aquifer. Therefore, the question is posed whether ATES is also feasible in less favorable conditions such as aquifers with varying redox conditions or aquifers characterized by sedimentary heterogeneity. The possibility to install ATES systems in such suboptimal conditions would largely increase the applicability of ATES in Flanders.In the first part of the study, the influence of ATES on groundwater chemistry is assessed by means of a literature review and a comparison of groundwater quality monitoring data at seven ATES systems with ambient groundwater quality values from 69 monitoring wells in Flanders. The seven evaluated Aquifer Thermal Energy Storage (ATES) systems are positioned in key aquifers, which contain major groundwater resources for the region. The results of the analysis of the hydrochemical data confirm that the small temperature differences (ΔT≤10) at which the ATES systems operate do not influence the concentrations of the main chemical constituents. Mixing of shallow with deeper groundwater during ATES operation, on the other hand, can alter groundwater quality. So, an integrated design of ATES systems taking into account the groundwater chemistry is very important, especially in phreatic aquifers and in the vicinity of public drinking water supply well fields.Well clogging due to iron (hydr)oxide precipitation is a widespread problem in aquifers with varying redox conditions from which the performance of ATES wells may also suffer. The interactions between physical and chemical processes during ATES operation are, however, not well understood. In the second part of the study, the reactive transport modeling code PHT3D is used to assess the effects of alternating pumping by ATES systems near the redox boundary on the precipitation of iron hydroxides for two cases in Flanders. Results show that in both investigated cases, initial mixing plays an important role in the development of Fe(OH)3 precipitation around the wells. The models further predict that even small temperature differences have a significant effect on the Fe(OH)3 concentration. Avoiding the mixing of oxygen/nitrate rich water with iron rich water remains the best strategy to prevent well clogging.Recent model studies indicate that meter-scale heterogeneities in the hydraulic conductivity field introduce considerable uncertainty in the distribution of thermal energy around an ATES system and can lead to a reduction in the thermal recoverability. In the third part of the study, the influence of centimeter-scale clay drapes on the efficiency of a doublet ATES system and the distribution of the thermal energy around the ATES wells is quantified. Multiple-point geostatistical simulation of edge properties is used to incorporate the clay drapes in the models. The results show that clay drapes have an influence both on the distribution of thermal energy in the subsurface and on the efficiency of an ATES system. The distribution of the thermal energy is determined by the strike of the clay drapes, with the major axis of anisotropy parallel to the clay drape strike. The clay drapes have a negative impact on ATES efficiency in the models without a hydraulic gradient. In the models with a hydraulic gradient, however, the presence of clay drapes has a positive influence on the efficiency of the ATES system. It is recommended to incorporate small scale heterogeneities in heat transport models to get a better estimate on ATES efficiency and distribution of thermal energy.To conclude, the results of this thesis show that the groundwater quality changes induced by ATES are rather small. However, phreatic aquifers are more vulnerable and especially near drinking water production sites, an integrated ATES design, taking the groundwater chemistry into account, is indispensable. Each feasibility study for ATES in aquifers with varying redox conditions should incorporate an analysis of the hydrochemistry at several depths. In this way, the well screen setting can be optimized and the risk of well clogging due to iron (hydr)oxide precipitation is reduced. A good insight in the heterogeneity of an aquifer is indispensable for a proper positioning of ATES wells, as even small scale sedimentary features can have a large impact on the distribution of thermal energy and on the efficiency of an ATES system.Dankwoord ... i Abstract ... iii Samenvatting ... v List of Abbreviations ... vii Contents ... ix List of Figures ... xi List of Tables ... xv 1 Introduction ... 1 1.1 Background ... 2 1.2 Research objectives and questions ... 4 1.3 Outline of the thesis ... 4 2 Influence of Aquifer Thermal Energy Storage on groundwater quality: A review illustrated by seven case studies from Belgium ... 5 2.1 Introduction ... 6 2.2 Influence of ATES on groundwater chemistry: a review ... 6 2.2.1 Temperature effects ... 6 2.2.2 Mixing ... 8 2.2.3 Conclusions ... 10 2.3 Materials and Methods ... 10 2.4 Results and Discussion ... 12 2.5 Conclusions ... 16 3 Reactive transport modeling of redox processes to assess Fe(OH)3 precipitation around Aquifer Thermal Energy Storage wells in phreatic aquifers ... 19 3.1 Introduction ... 20 3.2 Materials and Methods ... 21 3.2.1 Field Sites and Investigation Program ... 21 3.2.2 Pumping tests ... 23 3.2.3 Multiparameter measurements ... 23 3.2.4 Sampling and analysis ... 24 3.2.5 Reactive transport models ... 24 3.2.6 Conceptual Model and Model Discretization ... 26 3.3 Results and Discussion ... 28 3.3.1 Leuven case ... 31 3.3.2 Antwerp case ... 33 3.4 Conclusions ... 35 4 Modeling the effect of clay drapes on the efficiency of Aquifer Thermal Energy Storage ... 37 4.1 Introduction ... 38 4.2 Materials and Methods ... 39 4.2.1 Geological setting ... 39 4.2.2 Incorporation of clay drapes ... 39 4.2.3 Heat transport ... 40 4.2.4 Model setup ... 41 4.2.5 ΔT and Energy output ... 43 4.3 Results and Discussion ... 44 4.3.1 Thermal distribution ... 44 4.3.2 ATES efficiency ... 45 4.4 Conclusions ... 47 5 Conclusions ... 49 5.1 Introduction ... 50 5.2 Answers to research questions ... 50 5.3 Recommendations and perspectives ... 51 5.3.1 Recommendations on groundwater quality monitoring at ATES sites ... 52 5.3.2 Recommendations on reactive transport modeling of redox processes at ATES sites ... 52 5.3.3 Recommendations on incorporating heterogeneity in heat transport models for ATES ... 53 5.3.4 General recommendations and perspectives ... 53 A Time series of monitoring data from seven ATES systems and ambient concentrations ... 55 B Pumping test analyses ... 65 B.1 Introduction ... 66 B.2 Methods ... 66 B.2.1 Analytical Methods ... 66 B.2.2 Numerical model calibration ... 68 B.3 Results ... 69 B.3.1 Leuven case ... 69 B.3.2 Antwerp case ... 70 Bibliography ... 77nrpages: 104status: publishe

Application of multiple-point geostatistics to simulate the effect of small-scale aquifer heterogeneity on the efficiency of aquifer thermal energy storage

© 2015, Springer-Verlag Berlin Heidelberg. Adequate aquifer characterization and simulation using heat transport models are indispensible for determining the optimal design for aquifer thermal energy storage (ATES) systems and wells. Recent model studies indicate that meter-scale heterogeneities in the hydraulic conductivity field introduce a considerable uncertainty in the distribution of thermal energy around an ATES system and can lead to a reduction in the thermal recoverability. In a study site in Bierbeek, Belgium, the influence of centimeter-scale clay drapes on the efficiency of a doublet ATES system and the distribution of the thermal energy around the ATES wells are quantified. Multiple-point geostatistical simulation of edge properties is used to incorporate the clay drapes in the models. The results show that clay drapes have an influence both on the distribution of thermal energy in the subsurface and on the efficiency of the ATES system. The distribution of the thermal energy is determined by the strike of the clay drapes, with the major axis of anisotropy parallel to the clay drape strike. The clay drapes have a negative impact (3.3–3.6 %) on the energy output in the models without a hydraulic gradient. In the models with a hydraulic gradient, however, the presence of clay drapes has a positive influence (1.6–10.2 %) on the energy output of the ATES system. It is concluded that it is important to incorporate small-scale heterogeneities in heat transport models to get a better estimate on ATES efficiency and distribution of thermal energy.status: publishe

Influence of Aquifer Thermal Energy Storage on groundwater quality: A review illustrated by seven case studies from Belgium

AbstractStudy regionThe area of study is the northern part of Belgium (Flanders). The seven evaluated Aquifer Thermal Energy Storage (ATES) systems are positioned in key aquifers, which contain major groundwater resources for the region.Study focusThe increasing number of ATES systems leads to concerns by drinking water companies and environmental regulators about the long term impacts of ATES systems on the groundwater quality. This study assesses the influence of ATES on groundwater chemistry by means of a literature review, and a comparison of groundwater quality monitoring data at seven ATES systems with ambient groundwater quality values from 69 monitoring wells.New hydrological insights for the regionThe results of the analysis of the hydrochemical data confirm that the small temperature differences (ΔT≤10) at which the ATES systems are operating do not influence the concentrations of the main chemical constituents. Mixing of shallow with deeper groundwater during ATES operation, on the other hand, can alter groundwater quality. The results of this study, however, suggest that the groundwater quality changes are rather small, so that there is no immediate risk for the drinking water supply. However, the installation of ATES systems in the vicinity of public drinking water supply well fields should be handled with care, especially in phreatic aquifers

Aquifer Thermal Energy Storage (ATES) in phreatic aquifers, the role of redox conditions

Aquifer Thermal Energy Storage (ATES) generally is applied in relatively thick sandy layers under reduced conditions. But at many places in the world such optimal conditions for ATES do not exist. Therefore this research investigates the potential of ATES in (shallow) phreatic aquifers. By applying ATES in these conditions, the redox boundary should be taken into account. At greater depth the groundwater is reduced and often contains dissolved iron, at shallow depth the groundwater is oxygen/nitrate rich. Due to mixing of the oxidized water with the reduced water by extraction and injection during ATES operation, the dissolved oxygen and nitrate come into contact with the dissolved iron with precipitation of iron oxides and hydroxides as a result. These precipitates can cause well clogging, which especially will occur at the injection wells. Two cases in the north of Belgium (Flanders) are studied for the potential and restrictions of the application of ATES in aquifers where a redox boundary occurs. The first case investigates the potential of ATES in a thick phreatic sandy aquifer (Brussels Sands), but with a deep redox boundary in Leuven. In the second case the applicability of ATES is investigated in a shallow clay-rich sand layer (Berchem Sands) with a very shallow redox boundary in Antwerp. It turns out that in both cases the redox conditions play an important role in the feasibility of an ATES system. With the aid of accurate in situ hydrochemical measurements, groundwater analyses and mineralogical analyses, which are incorporated in a reactive transport model, the occurring processes around the ATES systems can be comprehended and predicted.status: publishe

Influence of Aquifer Thermal Energy Storage (ATES) on groundwater chemistry: an overview of several cases in Belgium

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Influence of Aquifer Thermal Energy Storage on groundwater quality: A review illustrated by seven case studies from Belgium

tStudy region: The area of study is the northern part of Belgium (Flanders).The seven evaluated Aquifer Thermal Energy Storage (ATES) systems are pos-itioned in key aquifers, which contain major groundwater resources for theregion. Study focus: The increasing number of ATES systems leads to concerns bydrinking water companies and environmental regulators about the long termimpacts of ATES systems on the groundwater quality. This study assesses theinfluence of ATES on groundwater chemistry by means of a literature review,and a comparison of groundwater quality monitoring data at seven ATES sys-tems with ambient groundwater quality values from 69 monitoring wells. New hydrological insights for the region: The results of the analysis of thehydrochemical data confirm that the small temperature differences (T ≤ 10)at which the ATES systems are operating do not influence the concentrations ofthe main chemical constituents. Mixing of shallow with deeper groundwaterduring ATES operation, on the other hand, can alter groundwater quality. Theresults of this study, however, suggest that the groundwater quality changesare rather small, so that there is no immediate risk for the drinking watersupply. However, the installation of ATES systems in the vicinity of publicdrinking water supply well fields should be handled with care, especially inphreatic aquifers.status: publishe

Assessment of Seasonal Aquifer Thermal Energy Storage as a Groundwater Ecosystem Service for the Brussels-Capital Region: Combining Groundwater Flow, and Heat and Reactive Transport Modeling

AbstractSeasonal aquifer thermal energy storage and recovery (ATES) help urbanized areas to contribute to their energy demands. We assess the potential of ATES in the Brussels-Capital Region, Belgium with groundwater flow, heat and reactive transport models. Situated in the phreatic Brussels Sand aquifer, they indicate that ATES systems are unfeasible for hydraulic conductivities of 4.2e-6 ms-1. At low groundwater flow velocities however, ATES are feasible for hydraulic conductivities of 1.4e-4 ms-1. Iron(hydr)oxide precipitation during ATES operation is investigated with reactive transport models. To avoid well clogging groundwater should be pumped only from above or below the aquifers redox boundary