The final report of the project COSMA describes the modeling results of four different scenarios regarding the pressure build-up in shallow aquifers due to the injection of CO2 into the sandstone aquifers of the Detfurth Formation. It is based on the “Technical Report on hydrogeological and static structural geological model implementation” (D 2.1) which focuses on the compilation of geological and hydrogeological background data (average values) and the development of a simplified conceptual hydrogeological model for a setting typical for the Northern German Sedimentary Basin as well as the model selection, model parameterization, definition of boundary conditions and implementation in hydrogeological flow model software packages. The hydrogeological model of the Cenozoic includes Quaternary and Tertiary aquifers down to the layer beneath the Rupelian clay. Moreover, a concept for modeling the interaction between deep, consolidated, saline aquifers with unconsolidated freshwater aquifers was developed. This report describes scenario analyses by using the numerical hydraulic model of the Detfurth Formation (Middle Bunter) and the simplified numerical groundwater model of the Cenozoic. The numerical models can be used to assess the key parameters, having an impact on the upconing of deeper saline groundwater beneath the well fields of water works (in shallow aquifer) due to imposed pressure signals.

Emerging subsurface activities (ESA) describe a set of methodologies and technologies using the earths subsurface for energy production or capture and storage of carbon dioxide. The earth’s heat is used as a clean source of energy (deep geothermal systems, DGS), process-related CO2 emissions can be stored in suitable geological formations (geological CO2 storage, GCS) and since the technique of horizontal drilling was developed, the exploitation of unconventional reserves of natural gas via hydraulic fracturing (shale gas extraction, SGE) expanded. At the same time, 97% of global freshwater resources are stored in the earth's subsurface, too, so that exploitation interests may come into conflict with the issue of groundwater and environmental protection. Main objective of deliverable D 3.1 of the COSMA-1 project therefore was to identify best practices of monitoring for geological carbon storage, deep geothermal systems and shale gas extraction projects with special focus on groundwater protection. Chapter 2 summarizes current groundwater monitoring standards, including monitoring network designs for emission-based (operators) and immission-based (water suppliers) monitoring. It further presents an identification of hazards related to ESA and a brief overview about the state of regulation. Finally, knowledge gaps concerning groundwater protection are identified. Chapters 3 to 5 describe for each of the above-named types of ESA the project stages and according monitoring needs and methods. Main target was to identify the key parameters and monitoring network designs ensuring reliable groundwater monitoring. As the most relevant hazards were drilling fluids, fracking fluids and brine migration as well as the mobilisation of methane, and the most likely pathways are leakages due to insufficient well integrity, for all three ESA types, pressure, temperature and TDS were recommended as key monitoring parameters. For shale gas extraction, in addition methane emission should be monitored. Key to any monitoring is i) the baseline sampling prior to the start of subsurface activities and ii) the adequate delineation of the area of review. All further monitoring to be implemented base on site-specific considerations and the authorities’ priorities. In any case, monitoring network should include the up-gradient, down-gradient and depth component. Monitoring wells and equipment should cover the full extension of horizontal bores and additional wells should be placed above potential pathways for fluid (or brine) migration as e.g. fault systems. The use of abandoned wells for monitoring is also recommended. The conception of appropriate monitoring strategies has further to be coordinated with the competent authorities, which have to control the compliance with all requirements. Therefore, site operator and water producer should report their monitoring plans and data at regular intervals to the competent authorities. The findings were summarized by transferring them to a risk management matrix following the Water Safety Plan (WSP) approach (WHO 2009). For shale gas extraction, deliverable D 3.2 will add specific mitigation measures to reduce the previously identified risk of negative impacts on shallow groundwater. Geological carbon storage was further investigated by means of the development of a coupled model for a theoretical case study site in the North-Eastern German Basin in the scope of work package 2 of the COSMA-project (D 2.3).

Increasing subsurface activities like geothermal energy production, unconventional gas exploitation (EGR – enhanced gas recovery), enhanced oil recovery (EOR) or geological carbon dioxide storage (GCS) are potentially hazardous for the environment. Especially fresh water aquifers used as drinking water resources need to be protected. The first phase of the project COSMA focuses on potential hazards and hazardous events arising from those activities and aims at developing an approach for quantifying and comparing potential risks. A general description of hazards and hazardous events resulting from emerging subsurface activities is given in the first deliverable D1.1 “Geological CO2 Storage and Other Emerging Subsurface Activities: Catalogue of Potential Impacts on Drinking Water Production”. In this 2nd deliverable, reported hazards and hazardous events resulting from geothermal energy production in Germany are described. This report includes analyses of enquiries to experts from all federal states, State Geological Surveys, information from standardization committees, developers, planners, drilling contractors, expert committees, consulting engineers and regulatory authorities such as environmental agencies, water authorities and mining authorities as well as from media reports. It aims to list and categorize observed impacts arising from recent geothermal projects, as there have been increasing activities in this field in the past 10 years in Germany and because there are many similarities to other subsurface activities with respect to drilling processes, fracking methods and reinjection of fluids. The German classification of geothermal systems distinguishes between shallow or nearsurface (< 400 m depth) and deep geothermal energy (> 400 m depth) systems, which will be used in the following chapters. Table 1 shows the difference to international classification schemes, regarding enthalpies and temperatures. The reported case studies of failures potentially leading to contamination of freshwater aquifers are described in chapter 2 with respect to the setting and the reason for failure (if known). Chapter 3 gives some recommendations with respect to possible precautions and countermeasures to prevent such potentially hazardous events. Regardless of the drilling depth there are general hazards and hazardous events that must be taken into account for all subsurface activities. Amongst these are hazardous events during operation which can lead to a contamination of the site, hazardous events during drilling caused by wrongly selected drilling techniques, drilling into unknown caverns, cavities or caves or faulty casing, construction or plugging (sealing). Furthermore, unexpected chemical reactions between fluids and casing or sealing material (e.g. grout) can cause seepage or leakage and therefore hydraulic short circuits. Table 2 gives a summary of general impacts of drilling, especially when multiple aquifers are intersected, as well as from operation of geothermal facilities. Further details are given in COSMA-1 report D 1.1.

The present study provides an overview of geogenic contamination, its occurrence, impacts and possible treatment options for drinking water production. Natural background and anthropogenic contamination can be differentiated using an algorithm based on the frequency distribution of measured substance concentrations. Case studies for geogenic contaminants such as ammonium, fl uoride, chloride, sulfate and uranium are discussed based on the origin, occurrence, controlling factors and treatment options. It is suggested that, in case of occurrence of geogenic contaminants, water must be treated or alternative sources need to be found, e.g., managed aquifer recharge, prior to the distribution as drinking water.

Within the context of continuously increasing CO2 concentrations in the atmosphere, as well as diminishing reserves of fossil fuels, finding new ways for autarkic and “climate friendly” energy production becomes more and more important. The development of emerging subsurfaces activities like Carbone Capture and Storage, and Hydraulic Fracturation might offer new options to tackle all three of the mentioned challenges. But, carbon capture and storage (CCS) and unconventional gas exploration (“hydro-fracking”) have in common that they impact parts of the subsurface and may thus potentially have an effect on fresh water aquifers. The combination of all the most recent studies about GCS and Hydro-fracking, allows the identification of a broad panel of key parameters that can assess and indicate a groundwater contamination resulting from emerging subsurface activities. Strong emphasis needs to be put on the fact that numerous new monitoring, verification and accounting tools are being developed worldwide threw researches programs. However, actually, it seems that the most efficient monitoring and early warning network should be based on the combined used of the most suitable (site-specific) geophysics and geochemicals tools.

The overall goal of the project Cosma-1: “Geological CO2 storage and other emerging subsurface activities” is the assessment of potential impacts of subsurface activities on shallow aquifers used for drinking water production. The first two deliverables (D 1.1 and D 1.2) dealt with general approaches for risk assessment and a description of potential hazards and hazardous events, which might be a risk for shallow freshwater aquifers, as well as lessons learned from existing geothermal energy production and storage sites in Germany. This Technical Report describes the activities of the second phase of the project COSMA-1 and focuses on the compilation of geological and hydrogeological background data (average values) and the development of a simplified conceptual hydrogeological model for a setting typical for the Northern German Sedimentary Basin. The hydrogeological model of the Cenozoic includes Quaternary and Tertiary aquifers down to the layer beneath the Rupelian clay. On this basis, a numerical model with the program Modflow (PMWIN 5.3) was implemented as no complex geometries had to be considered. The structural geological model of the target formation for underground utilisation, the Detfurth Formation (Middle Bunter), incorporates four different fault systems with nine faults in total enclosing the area of interest. Further, a concept for modeling the interaction between deep, consolidated, saline aquifers with unconsolidated freshwater aquifers in a setting typical for the Northern German Sedimentary Basin was developed. This included the model selection, model parameterization, definition of boundary conditions and implementation in hydrogeological flow model software packages. In the further course of the project, a scenario analysis will be performed by using the numerical hydraulic model of the Middle Bunter and the simplified numerical groundwater model of the Cenozoic. The numerical models will be used to assess the key parameters, having an impact on the upconing of deeper saline groundwater beneath the well fields of water works (in shallow aquifer) due to imposed pressure signals.