Hydrogeology is the summary term for all groundwater issues. Everywhere in the subsurface we encounter groundwater at some depth. This leads, for example, to a variety of consulting questions when work has to be done below the groundwater table. The groundwater level may be too high to build dry. Or there may be risks to the surroundings, such as subsidence, attracting groundwater pollution by pumping groundwater or damage to nature. But also questions about flooding, drought as a result of climate change, energy storage in groundwater, (hydro)chemistry and remediation of groundwater pollution are part of the discipline of hydrogeology. In the field of hydrogeology CRUX bases its advices on high quality knowledge and translates the knowledge into practice based on extensive experience. CRUX has knowledge of model codes, theoretical background of both the hydrological and mathematical side of hydrogeology and also develops new knowledge and numerical methods.
For the realization of a cofferdam below ground water level, a temporary lowering of the ground water level is needed. Examples can be found in simple drainage of small structures to very complex issues, from basements in inner cities to large-scale infrastructure projects. CRUX provides advice for the entire permit process for the Water Act in the form of drainage advice, environmental impact assessments, guidance and interpretation of pumping tests and support for the permit application at the Water Board, Water Board and Directorate-General of Public Works and Water Management. Here CRUX takes into account the wishes of the contractors, developers and the licensing authorities. CRUX is aware of the latest legislation and regulations in this area and maintains good contacts with the competent authorities. CRUX can also take care of supervision of the implementation of drainage and interpretation of the monitoring of drainage and environmental effects. For smaller excavation pits CRUX draws up practical brief drainage recommendations.
Statistics of groundwater levels are essential for geotechnical and geohydrological analyses and designs. Groundwater level statistics are practised with time series analyses of monitoring well measurements and spatial analyses. Here, CRUX can determine all necessary statistical key figures such as GHG, GLG, GG and recurrence times. When determining the groundwater statistics, not only the data and the theoretical arithmetic approach are considered, but also the multi-year trend in the measurement series and the practical application of the normative groundwater statistics in requirements analyses and standard determinations. CRUX regularly performs this work in (large) projects in the fields of housing and infrastructure, from tender to construction phase.
Besides applying statistical analysis to groundwater levels measured in the past, statistics can also be applied to expected groundwater levels in the future. As a result of climate change, groundwater levels may fluctuate more than in the past. This results in periods of both desiccation (groundwater level too low) and rewetting (groundwater level too high).
Statistical analysis answers questions such as: how much higher or lower is groundwater in the future and how often does this occur? Is desiccation to be expected in places where it is undesirable (natural areas)? Is dehydration to be expected in places where this is undesirable (residential areas)? In the case of groundwater damage: what part of the damage is due to climate and what part is due to project work (drainage)?
Large infrastructure projects often have a strong hydrogeological impact. This is accompanied by a wide range and diversity of hydrogeological issues. Examples are construction of new road networks, tunnels, rail and metro systems, maintenance of canals and rivers, construction of locks and realization of quay walls. The hydrogeologists of CRUX are involved in large infrastructural projects. For such projects advices are written on technical level with groundwater statistics, groundwater system analysis, drainage advices, barrier effect, drainage analyses and monitoring. In addition, CRUX consultants are involved in aspects outside the construction pit such as environmental influence and risks, supervision of permit procedures, requirements analysis and optimization of activities and risks.
Because CRUX is very experienced in the field of geotechnical engineering and foundation consultancy the connection between the two disciplines is great. Because groundwater (levels) and geotechnical means such as sheet piling influence each other this connection is of great added value. Examples where this is strongly expressed is in the analysis towards chances on settlement damage versus damage cases and the development of quay walls.
The scale of infrastructure projects often creates challenges and aspects that are not addressed in smaller dewatering projects.
Almost all governments stipulate as a precondition in designs that they must be built in a groundwater neutral way. The exact definition differs from place to place, but from a hydrogeological point of view it is a recurring issue with elements such as water balance, rewetting and dehydration, barrier effect and heat stress. In case of a large groundwater gradient, a barrier (basement) can even lead to settlement damage. CRUX uses knowledge of groundwater statistics, water system analyses and groundwater models to test designs for groundwater neutrality in accordance with the applicable rules.
Influencing the environment is actually caused by any change in the (ground) water system. Major environmental impacts are caused by, for example, drainage, alterations to quay walls, rivers and canals, and climate change (desiccation and water table change). Examples of environmental effects are ground level settlements at adjacent properties, monuments, archaeology or railroad tracks, displacement of groundwater contaminants, influence of soil energy systems and displacement of the freshwater-saltwater interface. The environmental impact can be calculated beforehand by means of a hydrogeological analysis in the drainage advice and environmental impact report.
In the determination of environmental effects the effects are assessed by CRUX. The assessment of effects is done by means of hard requirements and in some cases based on relatively flexible norms. Some norm violations are easy to measure while others only occur over time or in a specific season. Across this spectrum, CRUX is able to use models and statistical analysis to propose mitigation measures and monitoring strategies. In this way, the interests of the permitting authority, developer and contractor are represented to develop an effective design and solid implementation without harming the environment.
Groundwater monitoring provides insight into environmental influences and is therefore indispensable during activities such as cofferdam drainage, but also for policy aspects such as monitoring of desiccation. On the basis of groundwater monitoring, negative effects are detected at an early stage, thus minimizing the risk of damage.
CRUX employs several specialists with extensive experience in the field of soil energy. Innovations like the energy Sheet Pile were co-developed by CRUX. And in the larger drainage projects that potentially influence thermal storage systems we work with coupled hydraulic and thermal models to quantify the degree of influence.
More information on ATES.
By definition, chemical processes take place during construction activities in the subsurface. Think of clogging of drainage wells as a result of iron precipitation or calcification, influence of water glass and underwater concrete on groundwater quality, degasification of methane during deep dewatering, erosion of metals and displacement of components of a groundwater contaminant during dewatering. CRUX advises on geochemical aspects that occur during underground construction by means of risk analyses in the design phase, monitoring and interpretation of groundwater composition during (and after) the execution and damage analysis afterwards.
In addition, environmental effects such as displacement of groundwater contamination is a social issue with basic hydrogeological aspects and also hydrogeological solutions. Legally, relocation of contamination is not allowed. And if the remediation has already been designed or is already being carried out, then adjacent dewatering is a disturbance. Displacement of groundwater contaminations is considered by CRUX by means of modelling studies in combination with field and laboratory research. Displacements of groundwater contaminants are modelled by MODFLOW and Mt3d/Rt3d or PHREEQc.
The Special Geochemistry of Water Glass Injections outlines the issues of concern for drainage in construction pits with water glass injections.
See also the Special Geochemistry of Water Glass Injections