U. Sauer

Comparative study of geophysical and soil–gas investigations at the Hartoušov (Czech Republic) natural CO2 degassing site

Abstract Our study at this natural analog site contributes to the evaluation of methods within a hierarchical monitoring concept suited for the control of CO2 degassing. It supports the development of an effective monitoring concept for geological CO2 storage sites—carbon capture and storage as one of the pillars of the European climate change efforts. This study presents results of comprehensive investigations along a 500-m long profile within the Hartoušov (Czech Republic) natural CO2 degassing site and gives structural information about the subsurface and interaction processes in relation to parameters measured. Measurements of CO2 concentrations and investigation of the subsurface using electrical resistivity tomography and self-potential methods provide information about subsurface properties. For their successful application it is necessary to take seasonal variations (e.g., soil moisture, temperature, meteorological conditions) into consideration due to their influence on these parameters. Locations of high CO2 concentration in shallow depths are related to positive self-potential anomalies, low soil moistures and high resistivity distributions, as well as high δ13C values and increased radon concentrations. CO2 ascends from deep geological sources via preferential pathways and accumulates in coarser sediments. Repetition of measurements (which includes the effects of seasonal variations) revealed similar trends and allows us to identify a clear, prominent zone of anomalous values. Coarser unconsolidated sedimentary layers are beneficial for the accumulation of CO2 gas. The distribution of such shallow geological structures needs to be considered as a significant environmental risk potential whenever sudden degassing of large gas volumes occurs.

Joint interpretation of geoelectrical and soil-gas measurements for monitoring CO2 releases at a natural analogue

The development and validation of hierarchic monitoring concepts is essential for detecting and assessing possible leakages from storage formations, especially for carbon capture and storage (CCS) applications. Joint interpretation of various techniques (such as carbon dioxide (CO2) concentration and flux measurements, self-potential (SP) and geoelectrical surveys) showed that the combination of geophysical methods with soil-gas analysis for mesoscale monitoring of the shallow subsurface above geologic CO2 storages can be a valuable tool for mapping and monitoring potential CO2 spread in the subsurface. Three measurement campaigns were undertaken – May 2011, July 2011 and April 2012 – at an analogue site in the Cheb Basin, Czech Republic, with the aim of studying CO2 leakages and their temporal and spatial behaviour. Results of geoelectrical investigations give an insight into the structural features of the subsurface. CO2 discharge into the atmosphere is mostly impeded by shallow, clay-rich, partly water-saturated zones, which can be seen in the electrical resistivity tomography (ERT) results. Several transport processes can be identified based on SP measurements. The SP results highlight the complex behaviour of temporal variations for the flow patterns. In particular, coupled migration of gas and water plays an important influencing role in this process. Site-specific, near surface geological features and meteorological conditions seem to exert great influence on the degassing pattern and measured CO2 values. Therefore, soil-gas measurements represent a snapshot which illustrates both a distinct typical pattern of the soil-gas distribution in the near subsurface and certain differences caused by soil and meteorological conditions. Observed CO2 soil-gas anomalies and modelled results suggest that the occurrence of gas discharge is much more localized around restricted areas, often controlled by local permeability contrasts. Hence, our results show that a proposed monitoring concept should integrate SP, time-lapse ERT, meteorological parameters and soil-gas measurements to provide a comprehensive insight into the subsurface structures and processes.

Challenges associated with the atmospheric monitoring of areal emission sources and the need for optical remote sensing techniques—an open-path Fourier transform infrared (OP-FTIR) spectroscopy experience report

In recent years, OP-FTIR spectrometry has been successfully used to monitor hazardous air pollutants, greenhouse gases and other emission products. This ground-based remote sensing method has proven itself to be a flexible long-path technique for the characterization of large atmospheric volumes, enabling simultaneous detection of various volatile atmospheric compounds relevant for environmental assessment via a single rapid measurement. Within our research, we applied both active and passive ground-based OP-FTIR spectroscopy as a screening tool for the detection of fugitive greenhouse gas emissions. The method was proven as offering a suitable ‘compliance toolbox’ for continuous monitoring of the complex systems at the ground surface–atmosphere boundary, allowing large-scale identification and quantification of atmospheric composition over large areas to be achieved, in terms of identifying zones of higher leakage vulnerability. In this paper, we compiled our research results and highlight the adaption options of the field technology, illustrated measuring options and case studies at urban, natural and industrial sites. Furthermore, this technology was validated regarding its applicability in environmental atmospheric monitoring. The results show that passive OP-FTIR measurements offer the chance to achieve robust and reliable surveys in various arbitrary measurement directions to gain a comprehensive overview. However, to improve quantitative analysis in the case of weak sources, the application of an active open-path spectrometer is recommended. It should be noted that our investigations demonstrate that site-specific parameters such as prevailing wind directions, meteorological conditions, topographic influences, infrastructure, other artificial emission sources, and biological background need to be measured both prior to and during atmospheric monitoring and should be taken into account for comprehensive interpretation.

MONACO—Monitoring Approach for Geological CO2 Storage Sites Using a Hierarchical Observation Concept

The reliable detection and assessment of potential CO2 leakages from storage formations require the application of assurance monitoring tools at different spatial scales. Such tools also play an important role in helping to establish a risk assessment strategy at carbon dioxide capture and storage (CCS) facilities. Within the framework of the MONACO project (“Monitoring approach for geological CO2 storage sites using a hierarchical observation concept”), an integrative hierarchical assurance monitoring concept was developed and validated with the aim of establishing a modular observation strategy including investigations in the shallow subsurface, at ground surface level, and in the atmosphere. Numerous methods and technologies from different disciplines (such as chemistry, hydrogeology, meteorology, and geophysics) were either combined or used complementarily to one another, with results subsequently being jointly interpreted. Patterns of atmospheric CO2 distributions in terms of leakage detection can be observed on large scales with the help of infrared spectroscopy or micrometeorological methods, which aim to identify zones with unexpected or anomalous atmospheric CO2 concentrations. On the meso-scale, exchange processes between ground surface level and subsurface structures need to be localized using geophysical methods and soil gas surveys. Subsequently, the resulting images and maps can be used for selecting profiles for detailed in situ soil gas and geophysical monitoring, which helps to constrain the extent of leakages and allows us to understand controlling features of the observable fluid flow patterns. The tools utilized were tested at several natural and industrial analogues with various CO2 sources. A comprehensive validation of the opportunities and limitations of all applied method combinations is given and it shows that large spatial areas need to be consistently covered in sufficient spatial and temporal resolutions.

NovCare 2013 (Novel methods for subsurface characterization and monitoring: from theory to practice)

As safe and effective use of the subsurface environment is a major challenge facing our society, there is a great need to improve our understanding of the subsurface and to observe and investigate natural and anthropogenically influenced systems. Characterization of the subsurface includes the investigation of both groundwater and subsurface soils and their interaction processes. The range of monitoring tools used can be extended to include remote sensing tools [e.g., Fourier transform infrared spectroscopy (FTIR)], applicable at the near-surface to estimate gas–soil gas exchange processes. One example that highlights the importance of subsurface characterization and monitoring is the detection of groundwater contamination, to provide data for developing plans to prevent any further contamination and remediate existing contamination. With an increasing demand for investigation methods that have both high accuracy and resolution across a variety of spatial scales, there are several challenges for monitoring and exploration technologies in environmental research. These challenges include, among others, the identification and parameterization of system relevant physical, chemical, biological processes, as well as the determination of interactions between different scales. These challenges require high-resolution methods or novel data processing and common interpretation of data measured by different methods. In particular, cost-effective methods that are minimally destructive and can be rapidly applied are taken into consideration. Methods for subsurface characterization include e.g., geophysical, hydrogeological and direct push (DP) technologies, borehole-based, and tomographic methods. The NovCare conference (Novel methods for subsurface characterization and monitoring: from theory to practice— established in 2009) provides a platform to present and discuss state of the art developments and concepts. Existing methods are often refined and new methods are continually being developed. Therefore, this symposium presents recent developments, examples of field applications and introduces method concepts such as direct push, geophysical methods, adaptive (sensor) networks, and novel monitoring sensors. It also highlights the application of these methods in different thematic areas. The NovCare 2013 International Conference (Novel methods for subsurface characterization and monitoring: from theory to practice) took place from May 13–16th 2013 at the Helmholtz Centre for Environmental Research in Leipzig. This conference, which was organized by the Helmholtz Centre for Environmental Research, the University of Tuebingen, the Kansas Geological Survey and the Michigan State University, was the third successive annual conference. This conference series, which began in Leipzig in 2009 and then moved to Cape Cod in the US in 2011, has proven to be an excellent forum for exchanging ideas and experiences related to the challenges of subsurface characterization and monitoring. NovCare 2013 again provided a rare opportunity and an outstanding platform for researchers and practitioners from all over the world to exchange their ideas and experiences in dealing with the challenges of subsurface characterization and monitoring using a variety of methods. The conference had a strong interdisciplinary and international flavor, with around 100 participants from 13 countries taking part. Twelve companies and institutes presented their expertise and novel equipment and U. Sauer (&) P. Dietrich Department of Monitoring and Exploration Technologies, UFZ-Helmholtz Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany e-mail: uta.sauer@ufz.de

Application of open-path Fourier transform infrared spectroscopy for atmospheric monitoring of a CO 2 back-production experiment at the Ketzin pilot site (Germany)

During a controlled “back-production experiment” in October 2014 at the Ketzin pilot site, formerly injected CO2 was retrieved from the storage formation and directly released to the atmosphere via a vent-off stack. Open-path Fourier transform infrared (OP FTIR) spectrometers, on-site meteorological parameter acquisition systems, and distributed CO2 point sensors monitored gas dispersion processes in the near-surface part of the atmospheric boundary layer. The test site provides a complex and challenging mosaic-like surface setting for atmospheric monitoring which can also be found at other storage sites. The main aims of the atmospheric monitoring of this experiment were (1) to quantify temporal and spatial variations in atmospheric CO2 concentrations around the emitting vent-off stack and (2) to test if and how atmospheric monitoring can cope with typical environmental and operational challenges. A low environmental risk was encountered during the whole CO2 back-production experiment. The study confirms that turbulent wind conditions favor atmospheric mixing processes and are responsible for rapid dilution of the released CO2 leading to decreased detectability at all sensors. In contrast, calm and extremely stable wind conditions (especially occurring during the night) caused an accumulation of gases in the near-ground atmospheric layer with the highest amplitudes in measured gas concentration. As an important benefit of OP FTIR spectroscopic measurements and their ability to detect multiple gas species simultaneously, emission sources could be identified to a much higher certainty. Moreover, even simulation models using simplified assumptions help to find suitable monitoring network designs and support data analysis for certain wind conditions in such a complex environment.

Editorial: Thematic Issue for the International Conference: novel methods for subsurface characterization and monitoring: from theory to practice (NovCare 2015)

As societal concerns about the long-term sustainability of the quality and quantity of groundwater supplies mount, there is a pressing need to improve our understanding of the subsurface and to better monitor and characterize systems affected by natural and anthropogenic influences. Increasing demand for accurate and high-resolution investigation methods across a range of scales presents several challenges for the development of monitoring and characterization technologies. These challenges include, among others, the identification and parameterization of relevant physical–chemical–biological processes, as well as characterization of interactions between different scales. Addressing these challenges in a practical fashion calls for methods that are cost-effective, efficient, and minimally invasive. To address this issue and transfer methods to practice, NovCare 2015 had a strong interdisciplinary and international flavor, with approximately 100 researchers, consultants, regulators, and students from 9 countries gathered in Lawrence, Kansas, May 19–21, 2015, to participate in NovCare 2015. This was the fourth edition of the international, biennial conference series focusing on innovative methods for characterizing and monitoring aquifers, soils, and watersheds. The conference was organized by personnel from the Kansas Geological Survey and the Department of Geology at the University of Kansas (KU) and the Helmholtz Centre for Environmental Research (UFZ) in Leipzig, Germany. The conference was also supported by KU’s Office of the Provost and the KU Center for Research. In addition, ten private companies served as sponsors and exhibited at the meeting. NovCare 2015 showcased new developments and highlight examples of field applications of relevant approaches such as geophysics, direct-push technology, hydrogeological, and hydrogeochemical field methods, joint inversion of multi-method data, in situ measurements, wireless sensor networks, and remote sensing techniques. Session topics at NovCare 2015 included direct-push characterization of soils and aquifers, long-term monitoring, and opportunistic characterization (natural/anthropogenic stimuli and tracers of opportunity), characterization at the interface (stream–aquifer interactions and coastal settings), hydrogeological investigation techniques, integrated characterization of the unsaturated and saturated zones, geotechnical site characterization, and new tools for watershed characterization. In addition to the approximately 35 contributed oral presentations and nine poster presentations, nine keynote speakers presented recent developments in subsurface characterization. These keynote presentations spaned the full breadth of the conference thematic areas from airborne electromagnetics to in situ high-frequency monitoring of water chemistry. In addition, the meeting featured an afternoon field demonstration session showcasing direct-push methods for high-resolution subsurface characterization, surface and downhole methods based on nuclear magnetic resonance technology, distributed temperature sensing applications for groundwater flux measurements, and point measurements of groundwater velocity. The two tutorial-like seminars helped attendees This article is part of a Topical Collection in Environmental Earth Sciences on ‘‘NovCare 2015—Novel Methods for Subsurface Characterization and Monitoring: From Theory to Practice’’, guest edited by Uta Sauer and Peter Dietrich.

Ground-based Remote Sensing Using OP-FTIR Spectroscopy – A Feasibility Study for Application in Greenhouse Gas Control

Ground-based remote sensing by Open path Fourier-transform infrared (OP-FTIR) spectrometry provides data for the identification and quantification of emissions over wide surface areas. Large-scale OP-FTIR spectroscopy measurements are carried out associated with point-scale chamber-based soil CO2 flux measurement at a natural CO2 degassing area in the context of the hierarchical approach. The application of ground-based remote sensing using passive OP-FTIR spectroscopy represents a rapid and non-invasive assessment method for detecting variations in atmospheric concentrations of target gases and for the spatial identification of sources of increased gas concentrations. The presentation introduces results of a feasibility study investigating various scenarios such as urban regions, agricultural landscapes and natural CO2 degassing areas. Some examples of how to successfully deploy passive open path FTIR spectroscopy to identify anomalous greenhouse gas concentrations along greater optical pathways are presented.

Linking different Disciplines in a Hierarchical Approach to Identify CO2 Degassing Zones

The project MONACO aims to develop monitoring technologies for geological carbon dioxide storage, especially for identifying CO2 migration paths and leakages from the shallow subsurface into the atmosphere. Reliable monitoring of geological CO2 storage sites during and after the operational phase requires appropriate methods that provide the requisite information in real time. Within the frame of this project, an integrative hierarchic monitoring concept is proposed, with the aim of reliably detecting and assessing possible leakages from storage formations into the shallow subsurface (including aquifers and unsaturated zones, plus degassing of CO2 into the atmosphere). As part of this concept, several methods will be either combined or used complementary to one another and used at different scales, such as open-path Fourier transform infrared spectrometry (OP-FTIR), soil-gas analytics, geophysics and Direct-Push technology. This hierarchic approach is tested at a natural analogue site and first measurements indicate that this monitoring approach represents a multidisciplinary modular concept working in different scales and resolutions.