Groundwater Mapping

Denmark's commitment to groundwater protection began with the First Aquatic Environment Plan, which introduced regulations on phosphorus, nitrogen, and wastewater treatment. Cities were required to upgrade wastewater treatment facilities to meet higher environmental standards, and mandatory water metering was introduced for all consumers to reduce unnecessary water use.

To reduce water losses, Denmark implemented a Non-Revenue Water Penalty Tax, setting a 10% threshold for water losses. Water utilities exceeding this limit faced financial penalties, incentivizing better maintenance of infrastructure and reduced wastage.

This pivotal legislation emphasized groundwater protection as a national priority by identifying areas of special drinking water interest and initiating systematic groundwater mapping. Targeted action planning began to protect critical groundwater resources from contamination and overextraction.

• Zonation: Groundwater mapping advanced to include detailed vulnerability assessments and the implementation of targeted protection zones.
• EU Water Frame Directive: Denmark aligned its groundwater efforts with European standards, aiming to achieve good qualitative and quantitative status for all water bodies while preventing groundwater pollution and promoting sustainable water use.

The EU Groundwater Directive further reinforced the need to prevent hazardous substances from entering the groundwater. This directive set the stage for stricter monitoring and control measures to maintain groundwater quality.

• Structural Reform: The responsibility for groundwater management shifted from the State to local municipalities, decentralizing control and improving localized action plans.
• Protection of Near Borehole Areas: Denmark introduced targeted protection measures near boreholes to secure drinking water resources and reduce contamination risks.

The Water Sector Act introduced benchmarking requirements for water utilities to enhance efficiency and accountability. This act aimed to improve the operational performance of utilities while maintaining groundwater protection standards.

By 2015, groundwater mapping evolved into a continuous operational task rather than a one-time effort. This marked a shift to proactive, ongoing monitoring and maintenance, ensuring that Denmark's groundwater resources are consistently protected and sustainably managed.

Purpose

The foundation of groundwater mapping lies in gathering high-quality data from multiple sources. Key activities include:

• Collecting geophysical measurements, drilling logs, borehole data, and hydraulic head information.
• Utilizing national databases like the Jupiter Database (boreholes, water quality, and wells) and the Gerda Database (geophysical surveys).
• Analyzing historical data and reports to understand geological and hydrological conditions.

This phase ensures the availability of accurate and comprehensive data to guide subsequent steps. Gathering all available data is therefore neccesary to improve our knowledge and find the missing gaps.

Procedure

The foundation to success

Data is the cornerstone of the groundwater mapping process. Integrating public national databases and ensuring that all software can access the same data helps deliver consistent and high-quality results across the country.

Jupiter database

The Jupiter Database is Denmark's national database for groundwater, wells, and drinking water data. It contains information on over 450,000 wells and boreholes across the country. By centralizing this vast dataset, the database facilitates efficient analysis, planning, and decision-making. As a publicly accessible resource, it promotes transparency and collaboration in environmental management.

The Jupiter Database, managed by GEUS (Geological Survey of Denmark and Greenland), is a comprehensive repository of data essential for groundwater mapping and management in Denmark. It serves as a vital resource for researchers, municipalities, and policymakers relying on geological, chemical or hydrological data.

Purpose

The next step builds on the insights from the data assessment by addressing identified gaps. Guided by this evaluation, targeted surveys are conducted to gather new data, ensuring a robust foundation for future modeling and decision-making.

Along range of different surveys can be carried out e.g.:

• Geophysical surveys: SkyTEM, tTEM or other electromagnetic methods provide detailed images of the subsurface
• Streamflow or groundwater head measurements: Hydrological observational data is also a cornerstone in our groundwater modelling
• Groundwater chemistry: The chemical status of all the different aquifers also provide valuable insights into both the geological and hydrological setting, but is also vital for doing vulnerability assessments.

Procedure

Accurate and comprehensive data is essential for understanding the complexities of groundwater systems and making informed decisions to protect this important resource. The process involves integrating diverse datasets, each shedding light on different aspects of the subsurface and the water quality.

Groundwater systems are complex and influenced by a variety of geological, hydrological, and chemical factors. Therfore one must ask; what kind of data do I need? What is the target depth of investigation? What resolution do I need? Do I have enough groundwater head measurements?

Asking the right questions, allows you to gather the higest quality data, all of which is neccesary to carry out:

• Accurate Modeling: Building reliable geological and hydrological models requires precise inputs.
• Sustainable Management: Understanding the distribution, quality, and dynamics of groundwater is critical for long-term planning and protection.
• Risk Assessment: Identifying areas vulnerable to contamination or overextraction depends on robust datasets.

Purpose

The results of groundwater mapping campaigns are based on our best approximations of reality — models. By integrating data from surveys and databases, these models provide detailed visualizations of the groundwater system.

Every groundwater mapping campaign, generally comprises 3 types of models:

• Geological Models: Constructing a 3D representations of the subsurface to identify aquifer structures, clay thickness and general subsurface geometry.
• Geochemical Models: Assessing the chemical quality of groundwater and identifying problematic compounds like nitrates or pesticides.
• Hydrological/Groundwater Models: Simulating the groundwater flow, predicting aquifer behavior, and delineating transport zones over time used in general management

Procedure

The gological models are the basis of the modelling approach. Ensuring a well-founded and good geological model will give the best results in the end. The process of creating a geological model revolves integrating all the different data available and knowledge about the geological history and setting. Results from this is crucial in understanding the aquifer structure, geometry and protection. The developed models are of course used in the geochemical and hydrological models, but also by other parties e.g. creating environmental assessments, construction planning and munucipal management.

The geochemical modelling is a vital step for assessing the chemical state of the groundwater aquifers from which our drinking water ressource relies on. This is an important step in understanding problematic compounds in the local area and a neccesary step in ensuring a future-proof and sustainable ressource.

Lastly the hydrological modelling gives the actual results used in our delineation of areas and zones that should be protected for future-proofing our drinking water ressource. Generally, we create fully integrated hydrological modelling systems to simulate surface and groundwater flow and predict aquifer conditions. By doing particle tracking we attempt to understand exactly where the water we drink is formed.

Purpose

The purpose of the vulnerability assessments is to systematically identify areas of interest where our drinking water aquifers are vulnerable with regards to nitrate and other dangerous compounds. This is one of the core results from the groundwater mapping campaigns, where the areas needing targeted protection is found.. 

Procedure

Inside our areas of drinking water interest ("Future groundwater ressource") and inside our groundwater model calculated abstraction well catchments we delineate areas vulnerable to nitrate. The municipalities are hereafter responsible for identifying where they see that dedicated action is needed.

The vulnerability across the investigated domain is characterized as either limited, some or great vulnerability with regards to the geological properties of the area and the water quality.

This is highly detailed work and requires a well-developed geological model, extensive insights into the oxidation redox boundary and water chemistry in the area. All of this is compared in order of determining area that require protection.

Results

The final step of the groundwater mapping campaign is the designation of protection plans. These are specific plans used to safeguard the drinking water ressource. The groundwater abstraction catchments from boreholes, the well protection areas and the nitrate vulnerable areas are identified and stakeholders are engaged through public hearings to finalize and enforce the protection plans.

The results are finally made publically available (MiljøGIS) and used for planning and management across both the private and public sector in Denmark.

Challenges

Even though the groundwater mapping in Denmark has been going on for over 25 years, we are still facing multiple challenges. Especially pesticides and chemical substances in the groundwater is increasingly becoming a bigger and bigger problem. Furthermore, overexploitation in the major cities is becoming a serious challenge that needs to be adressed.  

Along with our general groundwater mapping and protection system we hope to address some of the problems our drinking water resource is facing at this moment by:

• Giving authorities the right legislation to make an impact
• Identifying the specific areas requiring targeted groundwater protection
• Providing financial assistance in order to protect the groundwater