Reactive-transport models contribute significantly to the field of modern geosciences. A general mathematical approach to solving models of complex biogeochemical systems is introduced. It is argued that even though mathematical models for reactive-transport simulations can be developed at various levels of approximation, the approach for their construction and application to the various compartments of the hydrosphere is fundamentally the same. The workings of coupled transport-reaction systems are described in more detail by means of examples, which demonstrate the similarities in the approach. Three models of the carbon dynamics in redox-stratified environments are compared: porous media flow problems in a coastal sediment and in a contaminated groundwater system; and a surface flow problem in a eutrophic estuary. Considering the interdisciplinary nature of such models, a Knowledge Base System for biogeochemical processes is proposed. Incorporation of the proposed knowledge base in an appropriate modeling framework, such as the Biogeochemical Reaction Network Simulator, proves an effective approach to the modeling of complex natural systems. This methodology allows for construction of multi-component reactive-transport models applicable to a wide range of problems of interest to the geoscientist.

The Dutch national research programme into the feasibility of retrievable storage of radioactive waste (CORA Programme Phase I; CORA: Comité Opslag Radioactief Afval = Committee on Radioactive Waste Disposal) examined the suitability of Tertiary clay deposits for such storage. Long-term isolation – up to 1 million years – of high-level radioactive waste under varying conditions is essential. A key concern is the hydro-mechanical response of the clay deposits in which radioactive waste might possibly be stored, in particular during glacial climate conditions as has happened repeatedly in the Netherlands during the Pleistocene. To evaluate this possibility hydro-mechanical computer simulations and mechanical laboratory experiments have been performed to analyse the effects of glacial loading by a thousand-metre-thick ice sheet on the permeability characteristics, fluid flow rates and the associated migration of radio-nuclides both within and out of Tertiary clays.

Glacial loading causes the expulsion of pore water from deeply buried clay deposits into adjoining aquifers. The rates and duration of the consolidation-driven outflow of water from the clay deposit, are very sensitive to the permeability of the clay and the dynamics of the advancing ice sheet. The maximum outflow rate of pore water is 1 mm per year. This rate is approximately three times faster than the flow rate of water in clay prior to ice loading. These preliminary simulation studies also indicate that cyclic loading can result in more rapid migration of radio-nuclides in clays. In clay deposits that are covered by a thick ice sheet, the contribution of dispersed transport relative to the total transport by diffusion amounts to 14%, assuming that there is no absorption of radio-nuclides by the clays and a longitudinal dispersivity of 50 m.

In this contribution, a case is made for the significance of sedimentation and sea-level change for groundwater management of coastal areas. In groundwater practice these geological processes are rarely considered. The role of sediment loading in causing anomalous fluid pressures and flow fields in relatively shallow aquifer systems is discussed and illustrated via both case studies and generic modelling studies. The role of sea-level changes in controlling current salinity distributions is discussed likewise. Central in the discussion is the concept of memory of groundwater systems, which provides the basic reason why processes that were operative in the geological past are still of relevance today. It is argued and shown that awareness and knowledge of the influence of sediment loading and sea level change on current hydrological conditions can lead to improved characterization of the distribution of hydraulic parameters and of the distribution of water quality in coastal areas. This improved characterization, in turn, serves to enhance the validity of impact assessment studies for the long-term development and management of those areas.

The hydrogeology of the Roer Valley Rift System is strongly influenced by the hydraulic properties of faults. The hydrogeological impact of faults is illustrated by examples from the SE Netherlands and the adjacent lignite mining areas within the Roer Valley Rift System, near Bonn in Germany. Hydraulic head discontinuities over the main faults in the latter area can be up to tens of meters as a result of extremely large groundwater extractions in combination with the relatively low conductivity of the main faults. Within the Netherlands, outside the mining areas, such large groundwater extractions do not take place, and groundwater fluxes are smaller. In this situation natural hydraulic head differences over the main faults are limited to several meters. Hydraulic head profiles over faults provide a first estimate of fault hydraulic properties that can be quantified using simple analytical solutions. The impact of faults on near surface processes is reflected in vegetation patterns and the structure of drainage networks, aquifer structure and hydraulic head patterns. Faults can thus be of great influence on transport processes in the subsurface as well as on water-related phenomena at the surface, and should accordingly be taken into consideration in studies related to water-management, contamination and environmental impact. Faults that have an enhanced vertical permeability are difficult to detect when horizontal groundwater flow is studied, which is probably the main reason why they are rarely described. Though, these faults may form important preferential paths to vertical groundwater flow.

A basin-scale hydrogeological study of the inverted northern Broad Fourteens Basin, Netherlands offshore, has resulted in a reconstruction of geological evolution, an estimate of Late Cretaceous topography and model scenarios of syn-inversion meteoric water infiltration. This study was performed in the scope of a basin-scale analysis of the hydrogeological setting and hydrodynamic evolution of the Broad Fourteens Basin. This analysis is aimed at obtaining quantitative knowledge of depositional history and hydrogeological parameters, and qualitative knowledge of hydrodynamic evolution of the Broad Fourteens Basin from Carboniferous to present-day. We present an overview of the tectonic and depositional history, the most likely hydrogeological setting and model scenarios of Late Cretaceous meteoric water infiltration in the northern Broad Fourteens area.

We constructed a detailed south-west north-east geological cross-section of the present-day northern Broad Fourteens Basin, and reconstructed Late Cretaceous basin geometry and topography. Using this geometry in a numerical model of density-dependent topography-driven fluid flow, we modelled several scenarios of meteoric water infiltration with estimated ranges of basin-scale permeabilities and water table head. Results indicate that a deep freshwater lens was developed during Late Cretaceous inversion, if the basin-scale hydraulic conductivity of the Rijnland and Altena Groups was at least 1⋅10-9 to 1⋅10-10 m/s, which is in general the highest value for claystones.

2D Basin modelling was used to evaluate the response of source rock maturation, and of petroleum expulsion, migration, accumulation and preservation to the evolution of the southern part of the inverted Broad Fourteens Basin. Modelling results show that the temperature, maturation and petroleum generation history as well as migration characteristics of both the Jurassic oil systems and the Carboniferous gas systems vary over short distances relative to the differences in burial history of the basin. Model results indicate that no major gas accumulations are preserved in the Slochteren Formation along the cross-section at present-day. Gas accumulations are predicted in sandstone-dominated Triassic units in the southern part of the section. Present-day oil accumulations predicted in the Vlieland Sandstone Formation sealed by the Vlieland Claystone Formation (in P9 and Q1 crestal structures) are in accordance with known oil accumulations. Additional oil accumulations are predicted in the sandstone-dominated Middle Werkendam Member, and in sandstones of the Delfland Subgroup.

The modelling offers an explanation for the different geochemical compositions of the accumulated oils in the P9 and Q1 areas. Modelling implies, that the oils in the Q1 oil field were sourced by remigrated oils expelled over time, from early mature to mature source rocks of the Posidonia Shale Formation. The biodegraded and water-washed nature of the Q1 oil is explained by the concentrated topography-induced groundwater flow through the Vlieland Sandstone Formation during the Late Cretaceous inversion of the basin. The oils accumulated in the P9 area were sourced from an early mature part of the Posidonia Shale Formation and were probably not affected by water washing and biodegradation because of post-inversion charging of the reservoir.

Surface and sub-surface expressions of shallow gas in the Netherlands part of the southern North Sea are described, using standard E&P 2D and 3D seismic surveys, as well as higher frequency acoustic surveys. Surface expressions observed are pockmarks, which are geomorphologic features at the seabed indicative for venting of gas, and cemented sandstones. The subsurface expressions found comprise both phenomena indicating efficient trapping of gas in reservoir sands, such as shallow bright spots and flat spots, and phenomena, which are indications of migration or leakage to the seabed. We refer to the latter as ‘seismic anomalies indicating leakage’. These anomalies include gas chimneys or seismic chimneys. All chimneys found in the area have in common, that they belong to a seepage style, which is called ‘small and localised’. Much of this seepage is situated over salt domes, with the accompanying normal fault above the domes acting as pathways for the gas or fluids. Although there is admixture of biogenic gas, it is believed that many of the features observed relate to thermo-genic gas.