S.E. Beaubien

Carbon dioxide and radon gas hazard in the Alban Hills area (central Italy)

Abstract The sudden and catastrophic, or slow and continuous, release at surface of naturally occurring toxic gases like CO 2 , H 2 S and Rn poses a serious health risk to people living in geologically active regions. In general this problem receives little attention from local governments, although public concern is raised periodically when anomalous toxic-gas concentrations suddenly kill humans or livestock. For example, elevated CO 2 concentrations have been linked to the death of at least 10 people in the central Italian region of Lazio over the last 20 years, while it was the CO 2 asphyxiation of 30 cows in a heavily populated area near Rome in 1999 which prompted the present soil-gas study into the distribution of the local health risk. A detailed geochemical survey was carried out in an area of about 4 km 2 in the Ciampino and Marino districts, whereby a total of 274 soil-gas samples were collected and analysed for more than 10 major and trace gas species. Data were then processed using both statistical and geostatistical methods, and the resulting maps were examined in order to highlight areas of elevated risk. General trends of elevated CO 2 and Rn concentrations imply the presence of preferential pathways (i.e. faults and fractures) along which deep gases are able to migrate towards the surface. The CO 2 and Rn anomalous trends often correspond to and are usually elongated parallel to the Apennine mountain range, the controlling structural feature in central Italy. Because of this fundamental anisotropy in the factors controlling the soil-gas distribution, it was found that a geostatistical approach using variogram analysis allowed for a better interpretation of the data. With regard to the health risk to local inhabitants, it was found that although some high risk areas had been zoned as parkland, others had been heavily developed for residential purposes. For example, many new houses were found to have been built on ground which has soil-gas CO 2 concentrations of more than 70% and radon values of more than 250 kBq m −3 . It is recommended that land-use planners incorporate soil-gas and/or gas flux measurements in environmental assessments in areas of possible risk (i.e. volcanic or structurally active areas).

Potential hazards of CO2 leakage in storage systems : learning from natural systems

Publisher Summary The aim of this chapter is to focus on the effects of increasing global atmospheric CO2 concentrations on plants and marine ecosystems, less is known about the effects of high, but very localized, CO2 concentrations originating from depth. It summarizes some of the findings from the EC-funded natural analogues for the storage of CO2 in the geological environment project (NASCENT) project, which studied a number of natural CO2 seeps throughout Europe. Of these, four sites were chosen for this chapter which, allowed different leakage processes and impacts to be assessed. One site was located in northern Greece, around the commercially producing florina CO2 gas field. The other three sites were in central Italy, including: a selected area of the latera geothermal complex, where natural deep CO2 migrates upwards along faults and is emitted to the atmosphere, the San Vittorino intermontane basin where CO2-charged ground waters cause extensive dissolution of limestone to form large sinkholes, and the Ciampino area to the southeast of Rome, where CO2 derived from deep-seated volcanism within the Alban hills complex migrates along faults in a residential area. Results indicate modifications in groundwater chemistry, sinkhole formation, and elevated toxic gas exposure risks in these areas caused by the occurrence of numerous active CO2 vents, however data also show that effects can be spatially restricted, and that health risks can be minimized with simple and inexpensive approaches and regulations.

NEAR-SURFACE GAS GEOCHEMISTRY TECHNIQUES TO ASSESS AND MONITOR CO2 GEOLOGICAL SEQUESTRATION SITES

As is well known the long-term effects and stability of a man-made CO2 geological storage facility is very difficult to predict with laboratory or modeling experiments due to the size and long time scales involved. Instead attractive additional sources of information are natural sites where CO2 produced at great depths is either trapped in porous reservoirs or leaks to the surface. These sites can be considered as “natural analogues” of what may occur over geological time spans within an engineered CO2 geological storage site. The study of these sites can be subdivided into three broad fields: i) understanding why some reservoirs leak while others don’t; ii) understanding the possible effects of CO2 should it leak into the near-surface environment; and iii) using the leaking sites to develop, test and optimise various monitoring technologies. The present article summaries many of the near-surface gas geochemistry results obtained in central Italy during the EC-funded NASCENT project (Natural Analogues for the Storage of CO2 in the Geological Environment). These include a comparison of leaking (Latera) and a non-leaking (Sesta) CO2 reservoirs, detailed soil gas surveys to outline migration pathways, the development of a geochemical continuous-monitoring station to study temporal changes in CO2 concentrations, and field experiments involving the injection of a gas mixture in the shallow subsurface to outline migration pathways and to understand the behaviour of various gas species based on their different chemical-physical-biological characteristics. Put together this data provides useful information for site selection, risk assessment and monitoring techniques, which is needed if CO2 geological storage is to become an accepted and widely-applied technology.

Soil gas as a monitoring tool of deep geological sequestration of carbon dioxide: Results from the three year Monitoring of the Encana Eor Project, Weyburn, Saskatchewan (Canada)

Publisher Summary As part of the IEA Weybum CO2 Monitoring and Storage Project, preliminary baseline soil gas data was collected in the summer and autumn of 2001 above the injection area of the EnCana Enhanced Oil Recovery project at the Weybum oilfield in south Saskatchewan. The 2001 data was presented at GHGT-6 in Kyoto. In the autumns of 2002 and 2003, further in situ monitoring of CO2, CO2 flux, O2, CH4, radon (222Rn), and thoron (220Rn) was carried out. Soil gas samples were also collected for the laboratory analysis of helium, permanent gases, sulfur species, and light hydrocarbons. All sampling was repeated over the same 360 point sampling grid and more detailed profiles for both follow-up years. Marked changes in CO2 levels (especially flux) for each of the three-year datasets indicated changes in surface conditions. The radon and thoron data was found to be similar for the three years, but appeared to vary in response to drift composition and seasonal effects, rather than migration from a deep source.

Geochemical and geophysical characterization of an active CO2 gas vent near the village of Latera, Central Italy

Publisher Summary A series of highly detailed soil gas sampling surveys have been conducted radially around various gas vents located within the Latera test site. Data indicate that active gas release occurs from a number of relatively small points on surface, implying that gas flow at depth is likely channeled along irregular gas-permeable pathways within a fault zone. To better interpret the results of these radial surveys a highly detailed horizontal profile of soil gas samples is performed across a number of the vents. If one assumes that majority of the measured trace gases all come from depth and that they are transported to surface via the high-volume advection of the thermo-metamorphically produced CO2, then, two important conclusions can be reached in regards CO2 sequestration applications. First, although it is foreseen that only CO2 is injected into a geological reservoir at depth, it must be remembered that if there is an eventual leak to surface the CO2 is likely transport other trace gases with it. Second, the different distribution of the various gas species in the shallow soil environment indicates the importance of this horizon to act as a buffer against the transfer of reduced gas species to the atmosphere. The efficiency of this buffer depends on the characteristics of the zone itself, such as unsaturated zone thickness, mineralogy, and gas permeability, as well as on the characteristics of the vent, such as flux rates and gas composition.

Use of the Panarea Natural Test Laboratory for Offshore CO2 Leakage Monitoring and Impact Studies

The natural CO2 leaking site near Panarea Island, Italy, has been used as a field laboratory to study potential impacts of CO2 on surface water chemistry and biology and to test innovative monitoring tools. Work involved 4 campaigns, one for each season, in which a 700 m long transect was sampled, benthic chamber measurements were made, and ADCP current measurements were conducted. In addition, an in house developed pCO2 continuous monitoring station was deployed for a 6 month period, during which it measured temperature and pCO2 values once every two hours and transmitted the values in real time to a web-based server. Results show the complexity of working at a real world site, as the dynamic marine system results in plume smearing and rapid dilution of the leakage signal. While making monitoring more difficult, this dilution means that impact will be limited (at least at leakage rates comparable to the Panarea site). In addition, the results also imply that future biological impact studies must take into account temporal variability, and not address only static pCO2 conditions.

Groundwater Changes Caused by Flow through Naturally Occurring Gas (±water) Leakage Points

Results from the EC-funded RISCS project are presented regarding groundwater sampling across two naturally occurring gas (±water) leakage points in central Italy to measure potential impacts, and evolution, of near surface groundwater chemistry. One site consists of gas only leakage in the Latera caldera, characterised by shallow alluvial sediments of volcanic (silicate) origin. The other site consists of gas and deep water leaking into a sinkhole in the San Vittorino valley, with surface sediments consisting of carbonate fluvial-lacustrine deposits. These contrasting characteristics permitted an evaluation of how site specific conditions can influence and control the potential impact of a CO2 leak on groundwater resources. Concentrations of most parameters were higher at the carbonate site despite having the higher, buffered pH. This is due to the flow of the deep-origin acidified waters through the thick carbonate stratigraphy and the higher solubility of the associated mineral phases. At the silicate site pH values less than 4 were found in the leakage area, with a clear control of major element chemistry exerted by the local potassium-rich volcanic sediments. Further down gradient the pH and dissolved concentrations for both major and trace elements approached that up gradient, non-impacted groundwaters.

GPR, TDR and geochemistry for the characterization of an active gas vent: development of monitoring strategies for CO2 geological sequestration sites

The migration of deep gas to the atmosphere along faults and associated structures is important in many fields, from studying the natural contribution of atmospheric greenhouse gases leaking from geothermal areas to ensuring the safety of man-made natural gas and carbon dioxide (C O2 ) geologic-storage sites. Near-surface geophysical and geochemical techniques were applied to a naturally occurring gas vent located along a deep terrestrial fault to better understand the structure and geophysical response of this gas-migration pathway. A number of ground-penetrating radar (GPR) profiles were first conducted across the vent. Spot samples were then measured along one of these profiles for in situ apparent permittivity (using time-domain reflectometry — TDR), complex permittivity on dried samples (using a capacitivecell), soil-gas composition, and clay and bulk mineralogy. Results show how the migrating gas induces secondary effects that modify the signature of the vent as seen in the GPR profiles. In particul...

Young sea ice electric properties estimation under non-optimal conditions

Sea ice monitoring is important for both climate change studies and potential trans-Arctic shipping. Ground Penetrating Radar (GPR) has been demonstrated to be a powerful method to retrieve sea ice thickness and gain information about its internal structure. Nevertheless, its applicability can be strongly limited in the case of very low ice thickness and high salinity content. This paper presents results from a field experiment performed under such conditions which integrated GPR data and s-parameters measurements with Vector Network Analyzer (VNA) on artificial sea ice grown at the SERF research site in Winnipeg, Canada. The observed dielectric behavior has been used to monitor sea ice growth, relating the electrical conductivity to temperature evolution and brine content. Results demonstrate the capability of both GPR and VNA techniques in the investigation of sea ice properties under non-ideal conditions.

Multidisciplinary Methodology Used to Detect and Evaluate the Occurrence of Methane During Tunnel Design and Excavation: An Example from Calabria (Southern Italy)

The occurrence of high volumes of methane during tunnelling operations is a critical safety factor that can influence the choice of different technical approaches for tunnel design and construction. Moreover, gas accumulation can be influenced by fluid migration along spatially focused preferential pathways (i.e. points along faults and fracture zones) that can result in highly variable gas concentrations along the tunnel trace. This paper proposes a methodological approach to minimise the risks, and costs, related to tunnel construction in rocks with potentially high methane concentrations. This approach combines soil gas geochemistry and structural geology surveys along and across the main faults and fracture systems that occur in the study area. The procedure is based on near-surface sampling and consists of a two-pronged approach: the measurement of fault zone gas emissions and their classification as barrier or conduit zones. Moreover, it is illustrated the importance of measuring a wide spectrum of different gas species, not just methane, for a more accurate interpretation of the geological, geochemical, and structural system. This is due to the potential for multiple gas origins, different gas associations, and various alteration and oxidation processes (e.g., CH4 oxidation into CO2) that can modify the geochemical signal along the flow path as gas migrates towards the surface.