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The study of the variability of soil gas concentrations is crucial for defining effective monitoring and remediation strategies and for the risk assessment related to the emission of vapors from the subsurface. The traditional soil gas monitoring strategy consists of seasonal surveys based on short‐time‐averaged sampling. Soil gas monitoring results are often used to assess the risk associated with the emission of volatile contaminants from the subsurface, using models mainly based on molecular diffusion and therefore assuming continuous emission from the soil. At two contaminated sites located in the Veneto region (Italy), continuous monitoring using a photoionization detector, pressure gauges, and an ultrasonic anemometer was used to relate soil gas variability to surface and subsurface physical parameters. At both sites a cyclic diurnal variation of volatile organic compounds concentration in soil gas was observed, correlated with the variation of several meteorological parameters and in particular with the variation of the differential pressure between soil and atmosphere and the buoyancy vertical flux. These findings question the reliability of the conventional methodology employed in the collection and assessment of soil gas data. Integr Environ Assess Manag 2024;20:2023–2032. © 2024 SETAC Key Points: Continuous monitoring at the two study sites showed that the cyclic variation of VOC concentration in soil gas correlated with the variation of differential pressure and buoyancy vertical flux.As evidenced by the differential pressure measurements conducted in this study, there is an alternation of nonemission phases, and phases in which the soil gas emission from soil to atmosphere may be enhanced due to pressure‐driven advective fluxes.The findings raise questions about the reliability of the conventional methodology employed in the collection and assessment of soil gas data. [ABSTRACT FROM AUTHOR]

A key challenge in helium (He) exploration is determining the efficacy of surficial soil gas surveys. While soil gas surveys can detect helium, the mechanisms leading to these signals are often poorly understood, hindering reliable interpretation for exploration purposes. Here we present the results of seven new He soil gas surveys (n = 1974) at the Akah Nez Field, Beautiful Mountain Field, Porcupine Dome area, Rattlesnake Field, Tom area, Tohache Wash area, and White Rock area, on the Colorado Plateau, Four Corners area, United States. Utilizing 2D seismic, well logs, and geophysical potential field data, structural maps were constructed of potential He reservoirs at depth and relationships were examined. Given geospatial relationships are being examined using the soil gas survey data, it is important to understand the mechanism that allows subsurface He to migrate upwards into the soil. In several fields interpreted basement faults act as migration conduits from the basement to the surface (i.e., leaky reservoir seals), and in other cases there is evidence for reservoir flank/crest fracturing likely due to differential compaction. Based on the regional geologic history, advective systems are likely responsible for the observed He soil gas signatures. Additionally, based on the Tohache Wash data (most prospective He area) an effective and risk-reducing novel technique is presented that constructs a predictive He exploration model utilizing soil gas geochemistry, high-resolution geophysical data, well data and seismic data using Bayesian ANOVA techniques, which may be translated to areas outside of the Four Corners area, United States. [ABSTRACT FROM AUTHOR]

Effective management of surface emissions from abandoned gob methane (AGM) is crucial for mitigating greenhouse gas emissions and ensuring public safety. An important geochemical characteristic of near-surface AGM migration is the potential presence of abnormal component concentrations in near-surface soil gas over abandoned coal gobs. To investigate this phenomenon, a surface geochemical survey was conducted based on four survey lines in the Dongyi and Dongsan abandoned gob groups in the Xinghua Coal Mine, Jixi Basin, in China. The gas chromatography technique was used to analyze the concentrations of methane, carbon dioxide, ethane, propane, and butane in the collected 43 soil gas samples. The results revealed a significant anomaly of soil gas concentrations, particularly methane and carbon dioxide anomalies, in the near-surface soil over abandoned gobs. The background concentration for methane was determined to be 7.49 ppm, with an anomalous threshold set at 10 ppm based on a statistical analysis and an iterative method. This threshold could be confirmed by examining the coupling and decoupling relationship between methane, carbon dioxide, and C2–3 as well. A spatial correlation between regions exhibiting anomalous methane and carbon dioxide concentrations and the positions of gob areas, abandoned surface wells, and faults was observed. Abandoned and sealed coalbed methane surface wells and faults near gas-rich gob areas have the potential to act as conduits for AGM leakage to the surface. Furthermore, concentrations of methane, carbon dioxide, and C2–3 in soil gas over abandoned coal gobs were significantly higher compared to areas unaffected by mining activities. This suggests that elevated concentrations of methane, carbon dioxide, and C2–3 in soil gas may originate from underground AGM. [ABSTRACT FROM AUTHOR]

A key challenge in helium (He) exploration is determining the efficacy of surficial soil gas surveys. While soil gas surveys can detect helium, the mechanisms leading to these signals are often poorly understood, hindering reliable interpretation for exploration purposes. Here we present the results of seven new He soil gas surveys (n = 1974) at the Akah Nez Field, Beautiful Mountain Field, Porcupine Dome area, Rattlesnake Field, Tom area, Tohache Wash area, and White Rock area, on the Colorado Plateau, Four Corners area, United States. Utilizing 2D seismic, well logs, and geophysical potential field data, structural maps were constructed of potential He reservoirs at depth and relationships were examined. Given geospatial relationships are being examined using the soil gas survey data, it is important to understand the mechanism that allows subsurface He to migrate upwards into the soil. In several fields interpreted basement faults act as migration conduits from the basement to the surface (i.e., leaky reservoir seals), and in other cases there is evidence for reservoir flank/crest fracturing likely due to differential compaction. Based on the regional geologic history, advective systems are likely responsible for the observed He soil gas signatures. Additionally, based on the Tohache Wash data (most prospective He area) an effective and risk-reducing novel technique is presented that constructs a predictive He exploration model utilizing soil gas geochemistry, high-resolution geophysical data, well data and seismic data using Bayesian ANOVA techniques, which may be translated to areas outside of the Four Corners area, United States.

222Radon (Rn) was proposed in the late 1990s as a naturally occurring tracer for light non-aqueous phase liquids (LNAPLs) in the subsurface, due to its preferential partitioning behavior in the non-aqueous phase, resulting in a reduction in Rn activities in areas with LNAPLs in the subsurface compared to unimpacted areas (Rn deficit). The Rn deficit technique emerged as a cost-effective, non-invasive, and sustainable method to rapidly identify and quantify LNAPLs, for the characterization and monitoring of contaminated sites. This paper presents an overview of the technique and its field applications, with a specific focus on the use of the method in the vadose zone based on soil gas Rn measurements. Although various configurations have shown favorable outcomes, limitations persist in the application of the soil gas Rn deficit technique. Deep LNAPL contamination, soil matrix heterogeneity, and temporal variations in Rn emissions pose challenges to quantitative evaluations of LNAPL contamination. Recognizing these factors is crucial for site-specific assessments. This review aims to highlight both the strengths and limitations of the method, providing insights into potential areas for future research while acknowledging the positive outcomes achieved in different configurations over the past decades. [ABSTRACT FROM AUTHOR]

The occurrence of sinkhole phenomena in Italy is a prevalent and very uncertain class of geological hazards that pose a significant threat to human infrastructure and individuals. These events are characterized by their unpredictability and the challenges associated with their accurate forecasting. Both natural and anthropic factors influence the occurrence of these events; therefore, accurate identification of the above factors is critical for effective proactive and predictive efforts. The work presented in this paper refers to a collapse that occurred in a volcanic region in northern Latium (central Italy) on 31 January 2023. The area has been monitored using drones since the early stages of the sinkhole's formation and has continued to date. Then, the collapse and the neighboring area were examined via geophysical and geochemical investigations to identify potential underlying factors. Geophysical and geochemical data were combined to provide a preliminary hypothesis on the collapse's genesis. The obtained data indicate that the structural collapse can be attributable to the fluctuation in groundwater levels as well as the development of instabilities along its banks, leading to a growth in its dimensions. [ABSTRACT FROM AUTHOR]

The potential risks of vapor intrusion (VI) can arise from low bulk soil contaminant concentration existing in shallow soils beneath a building foundation. To assess VI risks for such a contamination scenario, a comprehensive study was conducted on a factory building located at a trichloroethylene (TCE)-contaminated site. This study involved the integration of various types of field data, including groundwater, bulk soil, soil gas and indoor air data, along with the utilization of the Vapor Intrusion Screening Level (VISL) calculator. Previously observed high TCE concentrations in soil gas are attributed to accumulation of TCE vapor within the unsaturated soil beneath the building floor, since ground surface is extensively paved at this site. These soil gas data do not directly correlate with the magnitudes of bulk soil and/or groundwater TCE concentration with the linear adsorption model. Soil gas TCE concentration exceeding 107 μg/m³ (or bulk soil concentration exceeding 18.9 mg/kg) observed in shallow soils (at a depth of less than 1 m) may pose health risk to the workers inside the building due to VI, as we have detected TCE vapor concentrations exceeding indoor air screening level several times in the past. This bulk soil TCE concentration, however, falls below soil pollution control standards for TCE, i.e., 60 mg/kg, in Taiwan. As a result, soil remediation is not considered at this site. Soil gas TCE concentrations have reduced to less than 106 μg/m³ after two years of groundwater remediation work at this site. However, we have observed significantly higher soil gas TCE levels at a depth of 0.5 m compared to other depths. This discrepancy raises suspicions that an amount of TCE may still be trapped within the shallow soils that are not reached by groundwater table. [ABSTRACT FROM AUTHOR]

In the field of contaminated site remediation, risk analyses can be carried out by the use of appropriate mathematical models, based on simplified hypotheses of real sites. The possibility to have shared and accurate analytical methods is an important challenge for both routine laboratories and supervisory institutions. Although official methods (e.g., APH2009) are already available, they are lacking in some aspects, such as applicability to all the different sampling and analysis media and ease of use in routine analysis. Here, we report our recent advances in the implementation of an empirical method for hydrocarbon speciation in an air matrix, previously developed by the authors and published in 2015. The validation results led to a coefficient of variation (CV%) between 10–15% for the hydrocarbon fractions investigated (C5-C8 aliphatic, C9-C12 aliphatic, C9-C10 aromatic and C11-C12 aromatic) and recovery of ≤20%, in agreement with the required characteristics for the analytical methods. Several real samples were analyzed by the proposed method and the results were compared to those obtained by the official approach. The comparison led to an average bias (that is, the difference between the results from the developed method and those from the conventional one) of about 10%, confirming that the innovative approach is robust, accurate and can be applied to all the analytical media used for air sampling, such as soil gas. [ABSTRACT FROM AUTHOR]

Radon anomalies have been used for predicting earthquakes since radon is one of the most effective precursors. The radon time series analysis is the crucial phase to demonstrate the relationship between earthquakes and radon anomalies. A major part of the analysis is the characterization of its periodic and non-periodic components. This study aims to reveal the periodic components in the radon time series of the Manisa Fault Zone (MFZ). The results show that atmospheric pressure component S1 has been encountered in the radon time series. It is also found that radon concentrations were quite variable throughout the study period. [ABSTRACT FROM AUTHOR]

Radon gas and its radioactive daughters have been extensively studied on Mt. Etna, both in local volcanic rocks and in all types of fluid emissions from the volcano (crater gases, fumaroles, mofettes, soil gases, groundwaters). The first measurements date back to 1976 and were carried out both in local volcanic rocks and in the crater plume. Since then, fifty-four scientific articles have been published. The largest majority of them (more than 50%) correlated radon emissions with volcanic activity and/or magma dynamics inside Mt. Etna. Many others were focused on possible correlations between time variations of in-soil radon and tectonic activity. The concentration of radionuclides in Etna volcanic rocks was measured on several occasions in order to set background values of radon parents and to study the dynamics of Etna magmas. Some articles analyzed the concentrations of radon in Etna groundwaters and their temporal changes in relation to volcanic activity. Only a few studies focused on methodological aspects of radon measurements in the laboratory. Finally, in recent years, geoscientists began to analyze the possible negative effects on human health from high concentrations of indoor radon in houses near active faults. The overall results show that, in most cases, it is possible to understand the endogenous mechanisms that cause changes in soil radon release from rocks and its migration to the surface. Several physical models were produced to explain how those changes were correlated with Etna’s volcanic activity, making them potential precursors, especially in the cases of eruptive paroxysms. More complex is the analysis of radon changes in relation to tectonic activity. Indeed, if measurements of radon in soil is now considered a robust methodology for identifying buried faults, radon time variations are not always clearly correlated with seismic activity. This difficulty is likely due to the complex interplay between tectonic stress, magma migration/eruption and gas release through faults. In any case, the potential high hazard for human health due to high concentrations of indoor radon in houses close to faults seems to be a well-established fact, which requires particular attention both from the scientific community and the public health authorities.

Investigating the emissions of soil gas including radon, mercury and carbon dioxide (222Rn, Hg and CO2) from the solid earth to the atmosphere through active fault zones is of great significance for accession of atmospheric environment. In this study, the concentrations and fluxes of 222Rn, Hg and CO2 were measured at the main active fault zones at the western margin of the Ordos block, China. The concentrations of 222Rn, Hg and CO2 were in the range of 0–60.1 kBq m−3, 3–81 ng m−3 and 0.04–9.23%, respectively, while the fluxes of 222Rn, Hg and CO2 are in the range of 1.99–306.99 mBq m−2 s−1, 0–15.12 ng m−2 h−1 and 0–37.91 g m−2d−1, respectively. Most of the major fault zones at the study area are CO2 risk-free regions (CO2 concentration in soil gas < 5%). However, the extend of 222Rn pollution at the fault zones of F1, F4, F5 and F9 (the fault number) and that of Hg pollution at the fault zones of F2, F4, F5 and F7 were higher than the pollution level of 1. The annual emission of Hg and CO2 from the western margin of the Ordos block was estimated to be 2.03 kg and 0.70 Mt, respectively. Comprehensive analyses indicated that the higher emission rates of soil gases from the active fault zones were related to the seismic activities. The results suggest that the earthquake activity is a dominant factor enhancing the emission of 222Rn, Hg and CO2 from the solid earth through active fault zones and, furthermore, resulting great impact on the atmospheric environment. [ABSTRACT FROM AUTHOR]

In the region of large gas fields, extensive research has been conducted on earthquakes induced by industrial production in shale gas fields. However, limited attention has been given to the impact of post-earthquake events on shale gas reservoir leakage and fault activation. The Luxian M S 6.0 earthquake, which occurred on 16 September 2021 in the Luzhou shale gas field, has raised concerns about post-earthquake shale gas leakage. Post-earthquake measurements of soil gases (Rn, CO 2 , CH 4 , and H 2) and isotopic analyses (δ13C CO2 , δ13C CH4 and δD CH4) in the Luzhou shale gas field area reveal that the Huayingshan fault zone, a natural pathway for shale gas leakage, was not activated by the Luxian earthquake and did not exhibit any further shale gas leakage after the 2021 earthquake. Furthermore, the seismogenic fault, which was impacted by the earthquake, did not damage the shale gas reservoir, causing shale gas leakage. This study provides an important foundation for future research on shale gas extraction and seismic activity in the region. • Shale gas extraction induced earthquakes may not cause large-scale methane leaks. • The seismogenic fault, which was ruptured by the Luxian earthquake, did not result in shale gas leakage. • Induced earthquakes will not cause additional large-scale leaks from existing active faults in the surrounding area. • The occurrence of Luxian earthquake was induced by long-term wastewater injection and short-term hydraulic fracturing. [ABSTRACT FROM AUTHOR]

The northeastern Tibetan Plateau (NETP) is the most intensely uplifted deformation region in the Tibetan Plateau. The intense gas release caused by uplift has attracted widespread attention. In this study, we measured the soil gas concentrations (Rn and CO 2) and CO 2 fluxes from active faults and analysed the seismic tomography in the arcuate structure zone of the NETP. The results reveal that the concentrations and fluxes of Rn and CO 2 in the south area are higher than those in the north area. Factors such as rock types, meteorological conditions, and seismicity have limited influence on soil gas emissions. Instead, the uplift of the upper crust in the Tibetan Plateau plays a crucial role in determining the distribution of soil gases. Regions with high crack density (ε), saturation rate (ξ) and Poisson's ratio (σ) in the upper crust show stronger release, such as the epicenter of the Haiyuan M S 8.5 earthquake. The convergence zone of the arcuate structure zone with high crust uplift velocity is an intense release area with a rough total CO 2 output of ∼1.10 Mt.·yr−1. This output is twice the annual CO 2 output of the Wenchuan M S 8.0 earthquake rupture and one-fifth of the annual CO 2 output of Amiata volcano, Italy. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of natural source zone depletion (NSZD) will support an improved understanding of the long-term sustainability of NSZD as a site remedy and how NSZD rates may change over time. This is the first study that has quantified and compared the rate of three NSZD mechanisms (methanogenesis, vaporization, and aqueous biodegradation) between two chemically distinct light non-aqueous phase liquid (LNAPL) source zones (aliphatic-rich naphtha for Zone #1 vs aromatic-rich pyrolysis gasoline for Zone #2) within the same geologic and climate conditions. The rates of NSZD attributable to vaporization (400 mg C/m2/d vs. 300 mg C/m2/d) and aqueous biodegradation (92 mg C/m2/d vs. 67 mg C/m2/d) were similar for Zone #1 and #2; however, the rate of methanogenesis NSZD was 6x higher in Zone #1 (1000 mg C/m2/d vs. 170 mg C/m2/d). These results suggest that the aliphatic hydrocarbons content in an LNAPL source may be a factor in the rate of methanogenesis NSZD. For both Zone #1 and #2, total NSZD rate determined using this "three mechanism" measurement method was in reasonable agreement with two other methods used to measure total NSZD rates (CO 2 Gradient Method and Dynamic Closed Chamber Method), validating the "three mechanism" method as a tool to measure the total NSZD rate at a site and to provide an improved understanding of the predominant NSZD mechanism. Overall, this study highlights the importance of LNAPL type and chemical characteristics in determining source zone natural attenuation mechanism and its total rates. [Display omitted] • The rates of the three NSZD mechanisms were quantified and compared between two types of LNAPL. • NSZD via vaporization mechanism dominated the aromatic-rich LNAPL. • NSZD via methanogenic mechanism dominated the aliphatic-rich LNAPL. • LNAPL chemical characteristics determine the NSZD mechanism and its total rates. [ABSTRACT FROM AUTHOR]

In the field of contaminated site remediation, risk analyses can be carried out by the use of appropriate mathematical models, based on simplified hypotheses of real sites. The possibility to have shared and accurate analytical methods is an important challenge for both routine laboratories and supervisory institutions. Although official methods (e.g., APH2009) are already available, they are lacking in some aspects, such as applicability to all the different sampling and analysis media and ease of use in routine analysis. Here, we report our recent advances in the implementation of an empirical method for hydrocarbon speciation in an air matrix, previously developed by the authors and published in 2015. The validation results led to a coefficient of variation (CV%) between 10–15% for the hydrocarbon fractions investigated (C5-C8 aliphatic, C9-C12 aliphatic, C9-C10 aromatic and C11-C12 aromatic) and recovery of ≤20%, in agreement with the required characteristics for the analytical methods. Several real samples were analyzed by the proposed method and the results were compared to those obtained by the official approach. The comparison led to an average bias (that is, the difference between the results from the developed method and those from the conventional one) of about 10%, confirming that the innovative approach is robust, accurate and can be applied to all the analytical media used for air sampling, such as soil gas.

Fugitive gas migration (GM) from compromised oil and gas wells remains a global concern. To understand environmental impacts from GM there is a need to characterize the transport and fate of fugitive gas in the vadose zone. We simulated subsurface wellbore leakage by injecting natural gas into thick unsaturated glacio‐lacustrine deposits in a region of petroleum development in Western Canada. Methane and carbon dioxide effluxes were monitored and soil‐gas samples were collected for molecular and stable carbon isotope analyses. A conceptual model was developed to demonstrate the physical and biogeochemical processes that control the spatial‐temporal variability of GM. Methane oxidation partially attenuated natural gas; however, gas transport and fate were strongly influenced by variations in grain‐size distribution and barometric pressure, resulting in episodic effluxes and lateral gas transport. To accurately detect, quantify and assess GM at oil and gas sites, adequate site characterization and continuous, spatially dense monitoring are necessary. Plain Language Summary: Natural gas leaking from imperfectly sealed oil and gas wells can lead to explosive conditions in soil gas and methane emissions to the atmosphere. To understand the impacts and improve monitoring practices of fugitive gas migration, there is a need to characterize processes that control gas transport and fate in the unsaturated zone. We simulated subsurface wellbore leakage by injecting natural gas into thick unsaturated deposits in a region of petroleum development in Western Canada. The response was monitored by measuring methane and carbon dioxide concentrations and emissions on the ground surface and in soil gas in the unsaturated zone. Our results show that numerous compounding processes influence methane concentrations in the unsaturated zone and emissions to the atmosphere. While microbially mediated reactions consume methane in the unsaturated zone, variations in soil grain sizes and changes in barometric pressure strongly influence gas transport, which can lead to high episodic emissions in unpredictable locations. To accurately detect, quantify and assess fugitive gas migration at oil and gas well sites, adequate site characterization and continuous, spatially dense monitoring are necessary. Key Points: Fugitive gas migrated to the ground surface despite a deep vadose zone with low‐permeability silts and claysA preferential pathway and intervals of decreased barometric pressure resulted in a hotspot with high episodic methane effluxesLow‐permeability sediments and intervals of increased barometric pressure favored lateral gas migration and progressive methane oxidation [ABSTRACT FROM AUTHOR]

The recent detection of natural hydrogen seeps in sedimentary basin settings has triggered significant interest in the exploration of this promising resource. If large economical resources exist and can be extracted from the sub-surface, this would provide an opportunity for natural hydrogen to contribute to the non-carbon-based energy mix. The detection and exploration of hydrogen gas in the sub-surface is a significant challenge that requires costly drilling, sophisticated instrumentation, and reliable analytical/sampling methods. Here, we propose the application of a commercial-based sensor that can be used to detect and monitor low levels of hydrogen gas emissions from geological environments. The sensitivity, selectivity (K > 1000), and stability (<1 ppm/day) of the sensor was evaluated under various conditions to determine its suitability for geological field monitoring. Calibration tests showed that the hydrogen readings from the sensor were within ±20% of the expected values. We propose that chemical sensing is a simple and feasible method for understanding natural hydrogen seeps that emanate from geological systems and formations. However, we recommend using this sensor as part of a complete geological survey that incorporates an understanding of the geology along with complementary techniques that provide information on the rock properties. [ABSTRACT FROM AUTHOR]

Buried fault identification in plains is one of the important and difficult problems in current active fault research. Seismic activity forces crustal fluid to migrate up, especially along faults, thereby altering the geochemical characteristics of faults. Hyperspectral remote sensing has an extremely high spectral resolution; data derived from hyperspectral remote sensing have the capacity to detect physicochemical characteristics for mining or the subtle recognition of different underground objects. It provides a new method to detect changes in the geochemical characteristics in the fault. This study is trying to locate the fault by spectrum feature. The Xiadian fault was chosen as the study area. Several samples across the fault were collected, and these samples were measured by an ASD Field Spec 3 spectrometer(Analytical Spectral Devices, Boulder, USA, produced in 2008). Continuum removal, the spectral classification method and the wavelet transform technique have been used for spectral analysis. It has been shown that the spectrum of soil in the fault zone has some special characteristics that are different from those of the spectrum away from fault. Four special spectral regions, 550–580 ​nm, 600–700 ​nm, 700–800 ​nm and 800–900 ​nm, have been extracted as the singular ranges. These individual ranges could be used for fault location in the plain area. There is weak absorption near 880 ​nm of the sample in the fault, indicating that Fe3+ content plays an important role in fault identification and that the iron valences can indicate the fault environment. This study also found that the spectral anomalies in space could reflect the intensity of active tectonics to a certain extent. Therefore, spectral features have the potential to identify a buried faults. This study is the first to use spectroscopic techniques to analyze active tectonics, and there is a new discovery. This new discovery provides the basis for the application of remote sensing in the study of active tectonics.

The goal of the study is to investigate the relationships between soil gas composition and geological structures in a structurally complex area of the Carpathian fold and thrust belt. Surface geochemical surveys, aimed at determining the molecular and isotopic composition of soil gas samples, were carried out in the central part of the Polish Outer Carpathians in two major tectonic units, the Magura Unit and the Fore-Magura Group of units, which outcrop at the front of the former and within it as a tectonic window (the so-called Mszana Dolna Tectonic Window, MDTW). The tectonic structure of the area has numerous deformations, such as folds, thrusts, and strike-slip faults, that are accompanied by broad zones of mélange. In all 572 soil gas samples, the concentrations of light alkanes, gaseous alkenes as well as non-hydrocarbon (e.g. hydrogen) components were determined, and part of the samples were analysed to test the carbon isotope composition of methane and carbon dioxide. The results of the surface geochemical survey showed significant differences in the recorded microconcentrations of hydrocarbons within the tectonic units of the Outer Carpathians. Significantly higher concentrations of total alkanes C 2 -C 5 were mainly recorded in the MDTW, although the distribution of total alkane values within the Window shows strong connections with the arrangement of strata and the strike of faults and thrusts. Generally, the sealing is insufficient within the MDTW to support the existence of conventional economically viable hydrocarbon accumulations. Our data confirms the sealing role of the Magura Unit in the Carpathian oil system. Therefore, hydrocarbon sources (i.e. potential hydrocarbon accumulations) may be expected within the Fore-Magura Group beneath the cover of the Magura Unit. Our results are also of key importance for the interpretation of surface geochemistry data in other oil and gas provinces with a complex geological structure. • Surface geochemical signal varies depending on the tectonic unit in the Carpathians. • Geochemical signal indicates gas migration from Oligocene Menilite formation. • Surface geochemistry strongly supports hydrocarbon exploration in complex orogens. • C 2 H 6 /C 2 H 4 ratio determines the relative strength or activity of alkane migration. [ABSTRACT FROM AUTHOR]

A theoretical model is presented for balancing an acceptable radon concentration in indoor air. The infiltration of radon from the ground to the indoor air can be controlled by barriers or by lowering the air pressure at the lower zone of the ground slab. Indoor air with a radon concentration higher than that of outdoor air can further be controlled through the effective dilution of indoor air with outdoor air. The theory estimates the allowed radon infiltration from the ground to balance radon at an acceptable level indoors for a given ventilation rate, considering the radon contribution to the indoor air from indoor materials, building materials and the interior. A method using this theory is presented, identifying the necessary airtightness required for a radon barrier to balance the acceptable radon concentration for a building. Barriers include commercially used system solutions, such as bitumen-based radon blockers, wet-room membranes, reinforced fixed mortar pastes, and polyethene membranes. An acceptable indoor radon concentration of between 100 and 300 Bq/m3 in indoor air is used. Barriers are evaluated by their ability to prevent soil gas penetration from the ground in combination with their effect on the building durability, as barriers may create a far more vulnerable building. [ABSTRACT FROM AUTHOR]

This work reports radon-thoron monitoring at two depths (60 and 90 cm) and at 82 sites around Jawalamukhi thrust of NW Himalaya, India using Solid State Nuclear Track Detectors (SSNTDs). Further, radium contents of soil samples have been measured using NaI(Tl) crystal detectors and the exhalation rates have been measured using SMART Rn Duo monitor. The average radon-thoron concentrations at two different depths are found to be 3043 ± 691 Bq m−3, 4969 ± 561 Bq m−3 & 448 ± 416 Bq m−3, 773 ± 117 Bq m−3. Average value of area exhalation rate found to be 299.9 × 10−3 Bq m−2 h−1 with radium contents of value 51.04 Bq kg−1. The convective velocity of radon-thoron along with their flux densities has also been calculated. The average magnitudes of flux densities for radon-thoron found to be 44.96 × 10−2 Bq m−2 s−1 and 15.57 × 10−2 Bq m−2 s−1 whereas the convective velocities calculated to 8.38 × 10−6 m s−1 and 25.69 × 10−3 m s−1. The recorded values of thoron are lower than the recorded radon values. Moreover, the value of radon and thoron is higher at depth 90 cm than at depth 60 cm. The anomalous radon-thoron concentrations have been observed along the Jawalamukhi thrust and at some other sites suggesting secondary porosity or presence of local fault/lineament. A good correlation between area exhalation rates and radium contents, as well as between mass exhalation rates and radium has been observed. However weak correlation between porosity and area exhalation rates has been observed in this region. [ABSTRACT FROM AUTHOR]

Conventional analytical methods determine the concentration of compounds used to estimate the presence of environmental contamination capable of posing risk to human and ecological receptors. While these target analytes help regulators and environmental professional identify and manage potentially harmful conditions, these compounds can be generated by many natural and anthropogenic (man-made) sources and conventional methods alone fail to compositionally differentiate subsurface sources of contamination in complex environments. This case study demonstrates the advantage of using both conventional and forensic testing methods to accurately identify the source(s) of volatile hydrocarbon contamination in soil vapor samples for the development of an accurate conceptual site model in a neighbourhood near industrial facilities in Rio de Janeiro State, Brazil. The goal of this study was to differentiate potential impacts from a local steelmaking plant from fugitive hydrocarbons associated with more generic human activity in urban settings. This case study demonstrated the advantage of constructing chemical fingerprints from conventional volatile organic compound (VOC) method TO 15 and a forensic volatile hydrocarbon method using an enhanced version of method TO 15 (PIANO). The chemical fingerprints of vapor samples collected from subsurface soil gas and sewers were analysed and compared to laboratory reference samples. These data determined that the VOCs detected in neighbourhood soil vapor samples were associated with fugitive petroleum products migrating in the sewer pipelines and not with the steelmaking wastes emplaced near the residential area. This article discusses the forensic data and chemical signatures that support these findings, and the use of environmental forensic techniques to evaluate environmental data associated with complex scenarios, involving multiple contamination sources. [ABSTRACT FROM AUTHOR]

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Radon activity was measured in soil and groundwater at a number of locations in Purulia district of West Bengal, India, and radioactive doses in the local inhabitants due to exposure to radon in the environment were estimated. Spatial distribution of groundwater radon was found to be between 1.13 Bq/l and 457.35 Bq/l, while soil radon content was found between 2.13 kBq/m3 and 786 kBq/m3. Soil and groundwater radon near the Beldih Apatite mine were found to be significantly higher than other parts of the district, probably due to the presence of uranium mineralization of the region. [ABSTRACT FROM AUTHOR]

The new radiation protection law in Germany, which came into effect 2018, puts greater emphasis on the protection against naturally occurring radiation, especially radon as a known health hazard. The law requires the delineation of radon priority areas, where prevention and remediation of high indoor radon concentrations should be taken with priority. In Germany, radiation protection is the administrative responsibility of the federal states. The state of Hesse has early on decided to fully survey the state for radon priority areas. To identify radon priority areas, the geogenic radon potential has to be determined. To achieve that radon, soil-gas measurements combined with soil permeability are a necessity. The University of Applied Sciences (THM) in Giessen is responsible for the radon soil-gas measurement campaign in Hessen. To achieve a statistically sound survey of the state of Hessen with an achievable amount of different measurement locations, and in the given time-frame, a geology-based concept has been designed. Taking into account the known geological information about geological structures in combination with the administrative counties, a survey strategy has been established. Prior known information regarding soil thickness, moisture, digability, and other technical limitations are used to determine the exact measuring locations. At every location, the radon activity in soil gas is measured. The soil permeability is determined for every measurement as well. Three measurements are performed at each location. Having completed the first set of measurements, the design criteria of the campaign and the practical experiences will be presented.

Abstract Native hydrogen (H2) may represent a new carbon free‐energy resource, but to date there is no specific exploration guide to target H2‐fertile geological settings. Here, we present the first soil gas survey specifically designed to explore H2 migration in a region where no surface seepage has been documented so far. We choose the Pyrenean orogenic belt and its northern foreland basin (Aquitaine, France) as a test site for our strategy. The presence of mantle rocks at shallow depth (

The solvent-based sampling method for collecting gas-phase volatile organic compounds (VOCs) and conducting compound-specific isotope analysis (CSIA) was deployed during a controlled field study. The solvent-based method used methanol as a sink to accumulate petroleum hydrocarbons during the sampling of soil air and effluent gas. For each gaseous sample collected, carbon isotope analysis (δ13C) was conducted for a selection of five VOCs (benzene, toluene, o -xylene, cyclopentane and octane) emitted by a synthetic hydrocarbon source emplaced in the subsurface. The δ13C values obtained for gaseous VOCs (collected from soil gas and effluent gas) were compared to measurements obtained for the same VOCs present in the source material (none aqueous phase liquid - NAPL) and dissolved in groundwater to evaluate the reliability of the solvent-based sampling method in providing accurate isotope measurements. Since the NAPL source was composed of only 12 VOCs, potential bias related to the analytical procedure (such as co-elution) were avoided, hence emphasizing on field-related bias. This field evaluation demonstrated the capacity of the solvent-based method to produce precise and accurate δ13C measurements. The isotopic discrepancies between the gaseous and the NAPL values were < 1 ‰ for 39 out of the 41 comparison points, thus deemed not statistically different based on a common isotopic uncertainty error of ±0.5 ‰. Moreover, the current field study is the first field study to report δ13C measurements for up to five gas-phase VOCs obtained from the same sample, which appears to be of interest for VOC fate or forensic studies. The possibility to use several VOC isotopic measurements enabled by the sampling method would contribute to strengthen the connection assessment between gaseous VOCs and the suspected emitting source. Accordingly, the field results presented herein support the application of this sampling methodology to conduct CSIA assessment in the frame of VOC vapor studies. • Compound-specific isotope analysis (CSIA) was applied to gas-phase petroleum hydrocarbons. • Innovative sampling method specifically designed to conduct CSIA on gas-phase VOCs. • Method reliability is demonstrated at a controlled field site. • CSIA was performed for five petroleum hydrocarbons using a single field-collected sample, including laboratory duplicates. [ABSTRACT FROM AUTHOR]

Valley of Death, discovered almost half a century ago and located in the very upper reaches of the river Geysernaya, about 7 km from the Geyser Valley in Kamchatka, is famous for occurrences of dead animals there. During field work in August 2023, the soil CO 2 flux was measured using the accumulation chamber method in the lower section of the Valley of Death. On an area of 6.2 × 103 m2, the flux was measured at 100 randomly distributed points. At several points a MultiGas device was used for analysis of the composition of soil gases (СО 2 , H 2 S, SO 2). Data processing showed the presence of a single "hydrothermal" population of the CO 2 flux. The average CO 2 flux was found to be 1272 g m−2 d−1, with the maximum value of 28,984 g m−2 d−1. The average weight ratio of CO 2 /H 2 S was 14.7 ± 4, and thus, the "deadly" part of the surface of Death Valley in August 2023 emitted ∼8 t d−1 of CO 2 and ∼ 0.54 t d−1 of H 2 S. The soil temperature at the measurement points was close to the air temperature and did not correlate with the CO 2 flux. Such value of the CO 2 flux corresponds not <3.5 kg s−1 of hydrothermal steam condensed beneath the degassing part of Valley of Death. • The emission of CO 2 + H 2 S from of Valley of Death is realized from an area of 6.2 × 103 m2 of the lower part of the Valley. • The maximal and mean fluxes of CO 2 from Valley of Death are comparable with fluxes from the most active geothermal fields of the world. • The CO2 flux from Valley of Death corresponds to not <10 MW of the hidden convective heat flow beneath the studied area. [ABSTRACT FROM AUTHOR]

The recent detection of natural hydrogen seeps in sedimentary basin settings has triggered significant interest in the exploration of this promising resource. If large economical resources exist and can be extracted from the sub-surface, this would provide an opportunity for natural hydrogen to contribute to the non-carbon-based energy mix. The detection and exploration of hydrogen gas in the sub-surface is a significant challenge that requires costly drilling, sophisticated instrumentation, and reliable analytical/sampling methods. Here, we propose the application of a commercial-based sensor that can be used to detect and monitor low levels of hydrogen gas emissions from geological environments. The sensitivity, selectivity (K > 1000), and stability (

Non-Aqueous Phase Liquids (NAPLs) compounds are complex mixtures of organic liquids derived from petroleum and/or industrial activity. Contamination of soils and groundwater by NAPLs can generate health and economics problems by compromising water resources; restrict soils use; and cause damage to the public and private patrimony, and the environment. Today there is an increase in areas contaminated by different types of NAPLs, cause of great concern worldwide, due to the difficulty of locating and quantifying contamination, which is a major obstacle that prevents the cleaning of soils and groundwater in affected locations. This work aims to use the concentrations of the Radon gas in the soil as a way to determine areas contaminated by NAPL, using/prove the high affinity of the Radon for NAPLs, which causes the concentration of Radon in the soil to have a deficit in relation to that naturally observed in the studied region. After understanding the affinity of the Radon by the NAPLs, a gas station was located (with the contribution of the city hall of Belo Horizonte – Minas Gerais – Brazil), which went through a diesel oil leak from the storage tank making the area contaminated. Measurements of the Radon concentration were carried out with the AlphaGUARD® Radon monitor. These measurements confirmed the presence of a deficiency in the Radon concentration, which demonstrated its ability to be used as a marker for the presence of NAPL, contributing to future plans remediation and control of pollution, as well as studies of oil wells on-shore.

The Chuan–Dian region, situated in the middle part of the north-south seismic zone of mainland China in a highly deformed area of the eastern margin of the Tibetan Plateau, is one of the principal areas for monitoring earthquake activities in China. In this study, the geochemical characteristics of soil degassing (of CH4, H2, CO2, Rn, and Hg) and, the relationship between degassing and fault activity, were investigated in the Xianshuihe–Xiaojiang fault system (XXFS) at the eastern boundary of the Chuan–Dian rhombic block. The mean soil-gas concentrations of CH4, H2, CO2, Rn, and Hg in the XXFS were 8.1 ppm, 9.9 ppm, 0.5%, 15.1 kBq/m3 and 12.9 ng/m3, respectively. The δ13CCO2 and δ13CCH4 values of the hot-spring gases varied from −11.9‰ to −3.7‰ and −62.5‰ to 17‰, respectively. The He-C isotopic ratios indicate that the carbon in the northern and middle parts of the XXFS may have originated from deep fluids, whereas the carbon in the southern part of the XXFS is of organic origin. The high concentrations of soil gas were distributed near the faults, indicating that the faults could act as channels for gas migration. The distributions of the high soil-gas concentrations in the XXFS coincide with the highest stress and maximum strain rates, indicating that the fault activity enhanced permeability and increased the emission rates of the gases. The results of this study will be helpful for degassing in active fault zones and earthquake monitoring.

A theoretical model is presented for balancing an acceptable radon concentration in indoor air. The infiltration of radon from the ground to the indoor air can be controlled by barriers or by lowering the air pressure at the lower zone of the ground slab. Indoor air with a radon concentration higher than that of outdoor air can further be controlled through the effective dilution of indoor air with outdoor air. The theory estimates the allowed radon infiltration from the ground to balance radon at an acceptable level indoors for a given ventilation rate, considering the radon contribution to the indoor air from indoor materials, building materials and the interior. A method using this theory is presented, identifying the necessary airtightness required for a radon barrier to balance the acceptable radon concentration for a building. Barriers include commercially used system solutions, such as bitumen-based radon blockers, wet-room membranes, reinforced fixed mortar pastes, and polyethene membranes. An acceptable indoor radon concentration of between 100 and 300 Bq/m3 in indoor air is used. Barriers are evaluated by their ability to prevent soil gas penetration from the ground in combination with their effect on the building durability, as barriers may create a far more vulnerable building.

The Canary Islands are the only Spanish territory that holds potential for high enthalpy geothermal resources, although there is no evidence in the islands of hydrothermal fluid discharges in the surficial environment except for Teide volcano fumaroles in Tenerife. We herein report the results of several diffuse carbon dioxide (CO 2) degassing surveys carried out at six mining licenses across Tenerife (Berolo , Guayafanta , Abeque , Garehagua and Garehagua II) and Gran Canaria (Atidama), covering a total of 640 km2 and more than 3230 sampling sites. Selected geochemical molar ratios, spatial distribution of CO 2 efflux, statistical-graphical analysis of CO 2 efflux, isotopic composition of CO 2 (δ 13 C–CO 2), the calculated volcano-hydrothermal contribution of CO 2 and the deep-seated CO 2 efflux were studied. These data were combined and used for geothermal exploration, demonstrating an effective reconnaissance strategy that reduces risk and cost. Garehagua II , Garehagua (both located in the north-south volcanic rift of Tenerife) and Abeque (located in the northwest volcanic rift of Tenerife) are, in this order, the mining licenses studied that showed the highest potential to contain geothermal resources, based on the geochemical indicators ranking proposed. Image 1 • CO 2 degassing studies constitute a low-cost routine for geothermal exploration. • A multi-geochemical approach is successfully used to classify mining licenses. • The Canary Islands show environments with potential to generate electricity. • NS and NW rift zones in Tenerife show the highest geothermal interest. [ABSTRACT FROM AUTHOR]

The uses of waterproofing materials for insulation including required optimal thickness are discussed in this work. There exists a difference of five orders of magnitude in the diffusion coefficient of building materials along with the four orders of magnitude in the thickness and diffusion length. The radon resistance offered by materials varies with (a) thickness for given diffusion coefficient and (b) with diffusion coefficient with same thickness to diffusion length ratio (d/L). The earlier assumption of using thickness equal to three times of diffusion length is not workable for all materials but it causes an underestimation or overestimation. [ABSTRACT FROM AUTHOR]

Featured Application: Extensive long-term monitoring of greenhouse gases in soils. The mechanically simple and robust design makes the set-up an efficient, versatile, and reliable tool for soil gas monitoring, especially in forest soils. It can also be included in other routine monitoring networks with limited investment and relatively low additional labor costs. Soils provide many functions as they represent a habitat for flora and fauna, supply water, nutrient, and anchorage for plant growth and more. They can also be considered as large bioreactors in which many processes occur that involve the consumption and production of different gas species. Soils can be a source and sink for greenhouse gases. During the last decades this topic attracted special attention. Most studies on soil-atmosphere gas fluxes used chamber methods or micro-meteorological methods. Soil gas fluxes can also be calculated from vertical soil gas profiles which can provide additional insights into the underlying processes. We present a design for sampling and measuring soil gas concentration profiles that was developed to facilitate long term monitoring. Long term monitoring requires minimization of the impact of repeated measurements on the plot and also minimization of the routine workload while the quality of the measurement needs to be maintained continuously high. We used permanently installed gas wells that allowed passive gas sampling at different depths. Soil gas monitoring set ups were installed on 13 plots at 6 forest sites in South West Germany between 1998 and 2010. Until now, soil gas was sampled monthly and analysed for CO2, N2O, CH4, O2, N2, Ar, and C2H4 using gas chromatography. We present typical time series and profiles of soil gas concentrations and fluxes of a selected site as an example. We discuss the effect of different calculation approaches and conclude that flux estimates of O2, CO2 and CH4 can be considered as highly reliable, whereas N2O flux estimates include a higher uncertainty. We point out the potential of the data and suggest ideas for future research questions for which soil gas monitoring would provide the ideal data basis. Combining and linking the soil gas data with additional environmental data promises new insights and understanding of soil processes. [ABSTRACT FROM AUTHOR]

Spatial distribution characteristics and origin of soil gasses were discussed in this study. We also examine the correlation between the spatial variation of soil gasses and fault activity, based on the measurements of Rn, Hg, H2, and CO2 concentrations in the eastern segment of the BLT fault zone in the southern Tianshan Mountains, Xinjiang, China. The results show that the Rn and CO2 concentrations on the hanging wall were higher than those near the fault zone and on the footwall of the fault. Moreover, the Hg and H2 concentrations on the footwall were also higher than those near the fault and on the hanging wall of the fault. The main factors affecting the variations in soil gas spatial distribution were gaseous origin structure of the crust, fault activity, fault fracture degree, stratigraphic lithology, and the cover layer. The results of active structural fault mapping show that the BLT fault has been active since the Late Quaternary and the thrust has broken the fault surface. Under the influence of tectonic compressive stress, the tension zone was formed on the hanging wall of the fault and fractures were developed. This result is consistent with the characteristics of soil gas concentrations measured in this study, indicating that the concentrations of Rn, Hg, H2, and CO2 are closely related to the fault activity. These findings can be applied to identify seismic precursors from gas monitoring data of the studied area.

The objective of this paper is to evaluate the relationship between the distributions of direct and indirect, surface geochemical indices in the selected part of the Outer Carpathians. The research included analysis of molecular composition of soil gas samples and calcite contents as well as the measurements of magnetic susceptibility and pH of soil samples. The survey contained 96 soil gas samples collected from 1.2 m depth and 96 soil samples taken from interval 0.7–0.8 m depth. The maximum concentrations of methane, total alkanes C2–C5 and total alkenes C2–C4 were: 2100, 10.43 and 0.772 ppm. The magnetic susceptibility values changed from 3.6 to 21.5 x 10–8 m3/kg. The calcium carbonate contents varied from 0.02 to 29.92 wt% and the pH values measured in soil solutions obtained changed from 4.5 to 8.3. Although the results demonstrate no correlation between the direct soil gas anomalies and the indirect geochemical indicators, the integrated profiles in Fig. 7 suggest possible haloes in the calcite/magnetic data that could be related to hydrocarbons migrating from depth. There are, however, various independent mechanisms that might control the appearance of these mineral anomalies. Secondary changes of mineral composition of soils disclosed by the indirect methods, even if controlled by hydrocarbon migration throughout geological time, might cause some closure of migration pathways, influencing the location of active hydrocarbon migration pathways. Comprehensive interpretation of the results obtained by direct and indirect methods in this paper provides another positive example helping to better understand the complicated mechanism of hydrocarbon migration and the potential usefulness of indirect methods suitable for hydrocarbon exploration. [ABSTRACT FROM AUTHOR]

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Per- and polyfluoroalkyl substances (PFAS) are used in various industrial products; however, they pose serious health risks. In this study, soil, soil gas, and groundwater samples were collected at a PFAS manufacturing facility in New Jersey, USA, to determine the presence and distribution of PFASs from the soil surface to groundwater and at various distances from the presumed source. Fluorotelomer alcohols (FTOHs) were detected in soil (< 0.26–36.15 ng/g) and soil gas (160–12,000 E µg/m3), while perfluorinated carboxylic acids (PFCAs) were found in soil (4.3–810 ng/g), soil gas (<0.10–180 µg/m3), and groundwater (37–49 µg/L). FTOH and PFCA concentrations decreased as the distance from the presumed source increased, suggesting that PFCAs are likely to migrate in groundwater, whereas FTOHs primarily move in the vapor phase. The presence of PFAS in the groundwater, soil, and soil gas samples indicate its potential for vapor intrusion; thus, some PFAS may contribute to indoor air inhalation exposure. To the best of our knowledge, this is the first report on the quantification of volatile PFAS in soil gas at a PFAS manufacturing facility. [Display omitted] • Per- and polyfluoroalkyl substances (PFAS) pose serious health risks. • PFAS in soil, soil gas, and groundwater at a site in New Jersey were analyzed. • Fluorotelomer alcohols were detected in soil and soil gas samples. • PFCAs were found in soil, soil gas, and groundwater samples. • PFAS are capable of vapor intrusion. [ABSTRACT FROM AUTHOR]

Surface geochemical surveys were carried out in the Pawłosiów area in the eastern part of the Carpathian Foredeep. The research included an analysis of the molecular composition of soil gas samples as well as measurements of the calcite content, magnetic susceptibility and pH of soil samples. The results obtained were integrated with a geological-seismic model. Changes in the concentrations of total alkanes C 2 –C 5 in relation to changes in indirect geochemical indicators showed "compensatory" character. This means that in places where alkane concentrations were increasing, negative anomalies of magnetic susceptibility and a decrease in pH values were observed. It may be related to the intensity of the oxidation processes or reduction of the magnetic minerals in, as well as the reduced permeability of, the Miocene layers in the zones analysed. Moreover, the complex geochemical-geophysical interpretation showed a zone of anomalous values of the total C 2 –C 5 alkanes in the Pawłosiów area, which is suitable for prospecting. The research performed proved that a thorough analysis of the seismic record allowing subtle DHI anomalies appearing within the Miocene formations to be located, combined with the use of direct and indirect geochemical indicators, can help in identifying an area in terms of hydrocarbon potential. This applies in particular to this type of foreland basin, within which geological formations lie flat, and positive structures (anticlines) are hardly visible in seismic sections. In this type of structure, hydrocarbons can be accumulated in traps of a hybrid character (conventional and unconventional). The extensive zone of geochemical and geophysical anomalies found in the area of Pawłosiów may indicate the presence of this type of hydrocarbon accumulation. Comprehensive research, including direct and indirect geochemical methods in combination with a seismic survey, allows for a better assessment of the hydrocarbon potential of the studied area. • Direct and indirect surface geochemical indicators help interpret DHI seismic anomalies. • Alkane anomalies are associated with a decrease in magnetic susceptibility. • CH 4 and C 2 H 6 mainly migrate to the surface from shallow Miocene horizons, while C 3 H 8 and C 4 H 10 from deeper Miocene layers. • Integrated analysis of geochemical and geophysical indicators can help in the search for hybrid natural gas accumulations. [ABSTRACT FROM AUTHOR]