Matej Gedeon

Belgian Nuclear Research Centre

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Bart Rogiers

Belgian Nuclear Research Centre

Dirk Mallants

Commonwealth Scientific and Industrial Research Organisation

Marijke Huysmans

KU Leuven

Alain Dassargues

University of Liège

Okke Batelaan

Flinders University

Koen Beerten

Belgian Nuclear Research Centre

K. Vandersteen

Belgian Nuclear Research Centre

J. Marivoet

Belgian Nuclear Research Centre

Min Lu

Institute of Microbiology

Mieke De Craen

Belgian Nuclear Research Centre

Cooperative Institutions

Belgian Nuclear Research Centre

KU Leuven

National Fisheries Research and Development Institute

Vrije Universiteit Brussel

Chinese Academy of Sciences

University of Chinese Academy of Sciences

Commonwealth Scientific and Industrial Research Organisation

UCLouvain

Vuje (Slovakia)

University of the Philippines Diliman

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GEOSTATISTICAL ANALYSIS OF PRIMARY AND SECONDARY DATA IN A SANDY AQUIFER AT MOL/DESSEL, BELGIUM

Bart Rogiers Dirk Mallants Okke Batelaan Matej Gedeon Marijke Huysmans

Intheframeworkofthedisposalofshort0livedlow0�andintermediate0levelradioactivewasteina� near0surfacedisposalfacilityi nDessel,�Belgium,�additionalextensivesitecharacterizationhas� beenperformedin� 2008.� Thegathereddatanowenclose� 388� hydraulicconductivity� measurementsonsamplesof�8�coredboreholes.�Secondaryinformationasgrainsizeanalysis,� porosity,�andboreholegeophysicalparameterswasalsogathered.�Inaddition,�thegeologyofthe� studyareahasalsobeenthoroughlycharacterizedbyasetof�178�conepenetrationtests�(CPTs)� toapproximate�50�mdepth.�Thisdatasetallowedtorefinethehydrostratigraphicalmodelofthe� region.�Theexistinggroundwatermodel,�basedonlarge0scaleeffectivehydraulicproperties,�was� updatedaccordingly.�Thenextstepisasmall0scaleprobabilisticapproach�1)�tovalidatethe� currentexistingdeterministicgroundwatermodelsand�2)�tosupportdesignforamonitoring� network.�Inpreparationforstochasticrealizationsofthesubsurface,�ageostatisticalanalysisof� theavailableprimaryandsecondarydataisperformed.� Relationshipsbetweentheboreholelogsandthehydraulicconductivitymeasurementsare� examined.� Theconsideredlogsarethecaliper,� gammaray� (GR),� afocusedelectrolog� (Res_FEL),� andlong0� andshortspacingresistivitylogs� (Res_64,� Res_16).� Theselogsare� continuous,�andallowtogetsomeinformationaboutthehydraulicconductivityatthedepthsthat� werenotsampled.�Thisisespeciallyinterestingforstudyingtheheterogeneityofthedifferent� hydrogeologicalunitsandcalculatingarepresentativehydraulicconductivityforageological� unitoveritsentirethickness.�Thecorrelationcoefficientsbetweenthelogsandthehydraulic� conductivitydependstronglyontheconsideredgeologicalformation.� Forcertain� hydrogeologicalunits,�thecaliper,�gammarayandresistivitylogsshowacorrelationcoefficient� around�0.6�0�0.7�(Table�1).� Structuralanalysiswasperformedforallthehydrogeologicalunitstogether.�Figure�1�showsthe� variogramsandcross0variogramsthatarecalculatedusingCressie'srobustvariogramestimation� (Cressie,�1993)�afterstandardizationofeachhydrogeologicalunit.�Sphericalmodelsarefitted,�

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Hydraulic conductivity of Boom Clay in north-east Belgium

Li Yu Bart Rogiers Matej Gedeon J. Marivoet Mieke De Craen

Hydraulic conductivities of Boom Clay measured through various testing techniques in the laboratory exhibit similar K values in the order of 10 m/s. In situ measurements obtained from various scales at the HADES underground research facility yield K values that are very similar to values measured in the laboratory on samples of a few centimetres. Spatial analysis of K values across the Boom Clay at the Mol site reveals a typical profile with a very homogenous 61-m thick central part (the Putte and Terhagen Members), which is also the least permeable part of the Boom Clay. The geometric mean of the vertical (Kv) and horizontal (Kh) hydraulic conductivities for the Putte and Terhagen Members at the Mol site are 1.7×10 and 4.4×10 m/s, respectively, with a vertical anisotropy Kh/Kv of about 2.5. Higher K values, but still low (10 to 10 m/s), are observed in the more silty zones above and below. A regional analysis of vertical K variability of the Boom Clay in the northeast of Belgium confirms this typical K profile of the Boom Clay based on test results from other four regional boreholes. Furthermore, an increase in overall Boom Clay vertical hydraulic conductivity from the east towards the west in north-east Belgium was observed.

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Validation of simulated flow direction and hydraulic gradients with hydraulic head observations using open source GIS

EGUGA (2015)

K. Vandersteen Bart Rogiers Matej Gedeon

surements, in the framework of the environmental impact assessment of the near surface repository for low- and intermediate-level short-lived waste, realized by ONDRAF/NIRAS at Dessel, Belgium. Horizontal flow directions, horizontal and vertical gradients for the entire area of the groundwater model were estimated from measurements at shallow monitoring wells within the groundwater flow model domain, and compared to the flow directions and vertical gradients predicted by the model. For obtaining horizontal flow directions and gradients, triangulation of groundwater levels was performed for combinations of three neighboring hydraulic head observations in the same hydrogeological layer within the model. The simulated equivalents at the same monitoring wells were used to repeat the same methodology, and calculate flow direction components. This analysis was performed in SAGA GIS and was visualized through QGIS. Comparison of the flow directions and flow gradients obtained from measurements and simulations gives an indication on the model performance. The calculations were performed for three sandy hydrogeological units used in the model. A similar procedure was performed for the vertical hydraulic head gradients, where any combination of two hydraulic head observations at the same location but at different levels within the aquifer were used to validate the vertical gradients predicted by the model. Besides model validation on average hydraulic heads, the variability of flow direction and hydraulic gradients in time was checked, by using the actually measured monthly time series, to verify the applicability of the steady-state modelling approach. This basic assessment of flow directions and gradients using open source GIS can be used to identify potential areas of interest, were more detailed investigations would be recommended.

Hydraulic head

Hydraulics

Flow conditions

Groundwater model

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A comparison between hydrogeological modelling results and literature groundwater ages for shallow and deep aquifers in northern Belgium

Bart Rogiers Koen Beerten Matej Gedeon K. Vandersteen

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Building a staircase of confidence in groundwater modeling: a summary of ten years data collection and model development

Matej Gedeon Bart Rogiers Dirk Mallants

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Application of multi-scale variography for inferring the spatial variability of the hydraulic conductivity of a sandy aquifer

European geosciences union general assembly (2014)

Bart Rogiers Thomas Vienken Matej Gedeon Okke Batelaan Dirk Mallants

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel (Belgium), extensive characterization of the hydraulic conductivity (K) in the shallow Neogene aquifer has been performed at a regional scale. In the last few years the small-scale heterogeneity has been additionally characterized by outcrop analogue, hydraulic direct push, and borehole core air permeameter studies. The gathered data now include a) more than 350 hydraulic conductivity measurements on samples from 8 cored boreholes, mostly reaching depths of 50 m and data at 2 m intervals, b) more than 5000 air permeability measurements on the same borehole cores, c) more than 250 cone penetration tests (CPTs) with depths down to 40 m and data at 2 cm intervals, d) over 100 dissipation tests performed during the CPT campaigns, e) 17 direct push injections loggings, 6 hydraulic profiling tool logs, and 6 direct push slug tests, f) several hundreds of air permeability measurements on outcrop analogues of the aquifer sediments, and g) numerous grain size analyses. The current study aims to quantify the heterogeneity of K from the centimetre- to the kilometre-scale and to check the compatibility of the spatial variability revealed by the different datasets. This is achieved through gathering all K values (either direct measurements, calibrated relative K values, or K estimates from secondary data), and the use of variography to quantify spatial variability in terms of two-points geostatistics. The results are discussed, and the main differences between the different data sources are explained. In a final step, different multi-scale variogram models are proposed for capturing the main characteristics of multi-scale variability within the shallow Neogene aquifer in Belgium.

Permeameter

Outcrop

Aquifer properties

Geostatistics

Slug test

Variogram

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Exploring river–aquifer interactions and hydrological system response using baseflow separation, impulse response modelling and time series analysis in three temperate lowland catchments

Min Lu Bart Rogiers Koen Beerten Matej Gedeon Marijke Huysmans

Abstract. Lowland rivers and shallow aquifers are closely coupled and their interactions are crucial for maintaining healthy stream ecological functions. In order to explore river–aquifer interactions and lowland hydrological system in three Belgian catchments, we apply a combined approach of baseflow separation, impulse response modelling and time series analysis over a 30–year study period at catchment scale. Baseflow from hydrograph separation shows that the three catchments are groundwater-dominated. The recursive digital filter methods generate a smoother baseflow time series than the graphical methods, and yield more reliable results than the graphical ones. Impulse response modelling is applied with a two–step procedure. The first step where groundwater level response is modelled shows that groundwater level in shallow aquifers reacts fast to the system input, with most of the wells reaching their peak response during the first day. There is an overall trend of faster response time and higher response magnitude in the wet (October–March) than the dry (April–September) periods. The second step of baseflow response modelling shows that the system response is also fast and that simulated baseflow can capture some variations but not the peaks of the separated baseflow time series. The time series analysis indicates that components such as interflow and overland flow, contribute significantly to stream flow. They are somehow included as part of the separated baseflow, which is likely to be overestimated from hydrograph separation. The impulse response modelling approach from the groundwater flow perspective can be an optional method to estimate the baseflow, since it considers some level of the physical connection between river and aquifer in the subsurface. Further research is however recommended to improve the simulation, such as giving more weight to wells close to the river and adding more drainage dynamics to the model input.

Base flow

Interflow

10.5194/hess-2021-422

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The usefulness of outcrop analogue air permeameter measurements for analyzing aquifer heterogeneity: quantifying outcrop hydraulic conductivity and its spatial variability

Hydrological Processes (2013)

Bart Rogiers Koen Beerten Tuur Smeekens Dirk Mallants Matej Gedeon

Abstract Saturated hydraulic conductivity ( K ) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. Although several well‐established laboratory methods exist for determining K , in situ measurements of this parameter remain very complex and scale dependent. Often, the limited accessibility of subsurface sediments for sampling means an additional impediment to our ability to quantify subsurface K heterogeneity. One potential solution is the use of outcrops as analogues for subsurface sediments. This paper investigates the use of air permeameter measurements on outcrops of unconsolidated sediments to quantify K and its spatial heterogeneity on a broad range of sediment types. The Neogene aquifer in northern Belgium is used as a case study for this purpose. To characterize the variability in K , 511 small‐scale air permeability measurements were performed on outcrop sediments representative over five of the aquifer's lithostratigraphic units. From these measurements, outcrop‐scale equivalent K tensors were calculated using numerical upscaling techniques. Validation of the air permeameter‐based K values by comparison with laboratory constant head K measurements reveals a correlation of 0.93. Overall, the results indicate that hand‐held air permeameters are very efficient and accurate tools to characterize saturated K , as well as its small‐scale variability and anisotropy on a broad range of unconsolidated sediments. The studied outcrops further provided a qualitative understanding of aquifer hydrostratigraphy and quantitative estimates about K variability at the centimetre‐scale to metre‐scale. Copyright © 2013 John Wiley & Sons, Ltd.

Permeameter

Outcrop

Aquifer properties

10.1002/hyp.10007

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Variability in the hydraulic conductivity of the Boom Clay in the Campine Basin, NE-Belgium

Li Yu Bart Rogiers Matej Gedeon J. Marivoet Mieke De Craen

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Prediction of saturated hydraulic conductivity of a sandy aquifer at Mol/Dessel, using grain-size distributions and artificial neural networks