This study introduces a comprehensive methodology that integrates radiometric dating with gas chromatographic (GC) analyses of light non-aqueous phase liquids (LNAPL) recovered from monitoring wells at different filling stations. The aim is to evaluate the temporal evolution of LNAPLs in two distinct scenarios: natural attenuation (at site 1) and ongoing remediation activities (at site 2). The study period spans one year and four months, from June 2020 to October 2021. Throughout this time frame, the study monitored the progress of petroleum hydrocarbon biodegradation by analysing selected compounds: Total Petroleum Hydrocarbons (TPH), Sigma n-alkanes (C13 to C18), Sigma isoprenoids (C15 to C20), C17/Pristane and C18/Phytane ratios, and a specific biodegradation diagnostic index. The age determination provided reliable results for a single-point model release scenario (site 1). However, at site 2, where multiple LNAPL spills occurred, the age determination resulted in only an apparent age, due to the mixing of different fluids. Nevertheless, the unlike spatial distribution of the fluids offers some chances to estimate the age of the end members. The trend of the biodegradation in LNAPLs recovered from the two sites seems similar, pointing to a nearly complete removal of isoprenoids, independent of the initial values and whether or not there is an active remediation process. The main difference between the sites is the apparent tendency to the reduction of the heaviest (TPH) and more persistent compounds (such as pristane and phytane), probably triggered by the electrokinetic oxidation system taking place in the second site. The importance of these initial experimental findings lies in their ability to evaluate the site-specific response to pollutants, thereby enhancing the effectiveness of remediation efforts over time.

The raised sedimentary complex outcropping along the coastal belt just south of the Mogadishu airport is a roughly 10-m-thick carbonate-siliciclastic, coral-bearing depositional sequence. This complex is defined by eight primary depositional facies that form a transgressive-regressive sedimentary cycle, capped by a regressive surface that gently dips seaward. Facies analysis reveals a transgressive system tract consisting of a stratal set of siliciclastic sand deposited above a wave-ravinement surface, as indicated by an eroded quartz sand substratum. The transgressive succession continues with loose siliciclastic sand that contains a rich mollusk fauna intermixed with coarse skeletal debris of stony corals and both encrusted and articulated coralline algae. The macrofossil assemblage indicates diverse shoreface environments, where water depth, bottom morphology, and distance from the shoreline are critical in characterizing each facies. Comparisons with the modern biological zonation of the shallow shelf along the southern Somali coast have helped clarify the depositional characteristics of the Pleistocene facies succession. The distribution of fossil coral communities-often with colonies still in growth position-suggests a series of shallow-water facies related to back reef-shore environments that migrated landward over time. In contrast, the highstand system tract differs from the underlying facies by exhibiting a drastic decrease in the siliciclastic granular fraction and corals in growth position, which is offset by an increase in articulated and encrusted coralline algae that comprise most of the sediment source. Locally, skeletal rubble rich in large coralline algal nodules is typical of the regressive phase. The deposition of these facies results in a smoothing of seafloor roughness due to the burial of coral buildups by skeletal sand that shows less facies diversification. The marine succession-affected in its upper part by the calichification process-culminates in a marine terrace capped by aeolian sands deposited during various depositional-erosional events. Some of these deposits correlate with raised beachrock that outcrops discontinuously just above present sea level and corresponds to a minor Holocene sea level highstand. To assess the time interval required for the deposition of this transgressive-regressive cycle, which is related to a Late Pleistocene sea level positive peak, sedimentation rates and U-Th dating of two samples of massive Porites lutea from the transgressive system tract have been considered. The ages of approximately 114 kyr indicate a flooding event on the southern Somali coast during the transition between stages 5e and 5d of the Last Interglacial, while the overall duration of the sedimentary cycle is likely much less than 10 kyr. Furthermore, by matching the investigated cycle with positive peaks on significant global and local sea level curves, additional insights have been made regarding relative sea level fluctuations following the development of the Pleistocene sedimentary wedge.

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In the frame of a collaboration between the Italian National Research Council (CNR) and Mares s.r.l., a study, about the possibility of determining radon vertical distribution at different soil depths in order to trace light non-aqueous phase liquid (LNAPL) contaminations, was developed. The radon deficit technique, based on the preferential solubility of soil gas radon into non-polar fluids, such as refined hydrocarbons, has been investigated by various theoretical and applied research so far. According to international scientific literature, radon deficit can be used both for geochemical prospection of the spatial irregular NAPL dispersion and for monitoring of remediation activities. Even though it is well known that this type of pollutants can be distributed along the vertical soil profile-firstly due to their density in comparison to water density, and secondly due to fluctuations of shallow aquifers, soil pore size, aging of contamination, and so on-the vertical localization of the plume still represents a scientific challenge. In this article, a method to determine the radon vertical profile is tested and applied to assess the potential use of the radon deficit technique in the vertical detection of pollutant presence for the first time in a fuelling station. Two LNAPL-contaminated sites were selected for a pilot test. Experimental findings seem to support the use of vertical radon geochemical prospection to delimit the depth range of a LNAPL pollution directly. Systematic data collection and modeling may lead to a 3D reconstruction of the dispersion of contaminant in different soil levels.

A recent diesel spill (dated January 2019 ± 1 month) in a refilling station is investigated by the Radon deficit technique. The primary focus was on quantifying the LNAPL pore saturation as a function of duration of ageing, and on proposing a predictive model for on-site natural attenuation. A biennial monitoring of the local fluctuating shallow aquifer has involved the saturated zone nine times, and the vadose zone only once. Rn background generally measured in external and upstream wells is elaborated further due to the site characteristics, using drilling logs and phreatic oscillations. Notably, this study marks the first application of the Rn deficit method to produce a detailed Rn background mapping throughout the soil depth. Simultaneously, tests are performed on LNAPL surnatant samples to study diesel ageing. In particular, they are focused on temporal variations of LNAPL viscosity (from an initial 3.90 cP to 8.99 cP, measured at 25 °C, after 34 months), and Rn partition coefficient between the pollutant and water (from 47.7 to 80.2, measured at 25 °C, after 14 months). Rn diffusion is also measured in different fluids (0.092 cm2 s-1, 1.14 × 10-5 cm2 s-1, and 2.53 × 10-6 cm2 s-1 at 25 °C for air, water and LNAPL, respectively) directly. All parameters and equations utilized during this study are introduced, discussing their influence on Radon deficit technique from a theoretical point of view. Experimental findings are used to mitigate the effect of LNAPL ageing and of phreatic oscillations on determination of LNAPL saturation index (S.I.LNAPL). Finally, S.I.LNAPL dataset is discussed and elaborated to show the pollutant attenuation across subsurface over time, induced by natural processes primarily. The proposed predictive model for on-site natural attenuation suggests a half-removal time of one year and six months. The significance of such models lies in their capability to assess site-specific reactions to pollutants, thereby enhancing the effectiveness of remediation efforts over time. These experimental findings may offer a novel approach to application of Rn deficit technique and to environmental remediation of persistent organic compounds.

Soil and groundwater contamination by NAPLs (Non-Aqueous Phase Liquids) is certainly a big issue for protecting the environment. In situ clean-up actions are routinely applied to mitigate the risk and are supplemented by monitoring surveys to assess the degree, extension, and evolution of the contamination. Radon gas is here used as a tracer of contamination because of its high solubility in non-polar solvents that produce a reduced concentration of the gas in polluted soil and groundwater with reference to radon levels in adjacent “clean” areas. This approach was employed in two sites where gasoline and diesel spillage occurred, causing soil and groundwater contamination. The two case studies were chosen because of their difference in terms of the hydrogeological features, age of the spillage, composition of residual NAPLs, and clean-up measures to test the advantages and limits of this approach in a variety of settings. Radon data, NAPL concentration in the groundwater (mainly total hydrocarbons, Methyl Tertiary-Butyl Ether and Ethyl Tertiary-Butyl Ether) and the depth of the groundwater table were periodically collected in surveys that spanned a period of two years. This dataset was statistically processed using principal component analysis to unravel which factors and attenuation processes are working in the sites and the response of the radon deficit approach to this complex series of phenomena concurrently occurring there.

Abstract In the frame of a collaboration, between CNR-IGAG and Mares s.r.l., on the triennial project “CANDAC-Mares 2020” about the study of Non-Aqueous Phase Liquid (NAPL) contaminated sites, the Laboratory of Environmental Radioactivity, IGAG-CNR Montelibretti organized a study on the possibility to determine on-site radon vertical distribution as NAPL contamination tracer at different soil depths. Rn deficit technique, based on preferential solubility of natural radiogenic soil gas Rn into non-polar fluids, such as refine hydrocarbons, has been studied in various theoretical and applied researches so far. According to international scientific literature, Rn deficit can be used both in geochemical prospection of the areal irregular pollutant distribution and in monitoring of remediation activities successfully. Unfortunately the vertical location of the plume still represents a scientific challenge even though is well known this type of pollutant can be distributed along the vertical soil profile due to its density in comparison to water density, fluctuations of shallow aquifers, soil pore size distribution, aging of contamination and so on. In this article, a method to determine Rn vertical profile is tested and applied to assess Rn deficit technique applicability in vertical detection of pollutant presence for the first time in a fuel station. Two NAPL contaminated sites are selected for a pilot test. Results obtained seem to support the use of vertical Rn geochemical prospection for a 3D complete reconstruction of contaminant dispersion in different soil levels in order to monitoring plume changes during time due to natural attenuation and/or remediation activities.

Non-polar liquids released in environment cause a long-term soil and groundwater contamination. The costs associated with a multi-year remediation are high and the uncertainty in the allotment of legal responsibilities could defer the decontamination planning. Therefore, a reliable method to assess the residence time of spilled Non-Aqueous Phase Liquids (NAPLs) in soil is highly needed. In this paper, a method, using low environmental radioactivity and radiometric dating, is described and applied to real contaminations. After being alpha-recoiled from 232Th in soils,228Ra accumulates in light NAPLs, generating 228Th. A disequilibrium clock, based on gamma-spectrometric determination of the ratio 228Th/228Ra, was conceived to measure the residence time of LNAPL pollutants in a soil. The pollutant extraction and gamma-counting procedures are described. This approach inverts the role played by pollutants and contaminated matrixes, because the flux of alpha recoil from soil generates in pollutants a reliable model of "closed system", which is preserved in LNAPLs due to the peculiar properties of non-polar liquids. All case studies are sited in Italy and have been supported by preliminary lab tests. Dating tests of 15 samples (including LNAPLs, contaminated soils and oil socks) were performed, in most cases, blindly. Then, the results were compared to historical data about contaminations. A good correlation between test results and site history was generally obtained. But an increasing error has to be considered in old contaminations due to the nonlinear nature of disequilibrium time equation. Other reasons of discrepancies, due to system opening, include the use of surfactants, the presence of significant amount of MnO2 in soil and the interactions of different spillages. The outcomes of this research evidence the possibility to precisely date the contamination both in soil and in non-polar liquids, offering a potential tool to settle legal disputes. Further studies could broad and improve the applicability of the method.

Groundwater age can differ when determined by radioactive tracers due to different retardation factors. According to Krishnawami et al. 1982, Radon isotopes supply to groundwater is considered as a measure of the supply of Radium isotopes. This assumption considerably affects the estimation of the Ra retardation factor. Briganti et al. 2020 reports how the different groundwater supply mechanisms of Ra and Rn should be considered in order to avoid a relevant variation between the real water residence time and the age calculated. In the same work an alternative method for estimating Ra retardation factor is proposed without using Rn data as a comparison term. A synthesis of the main results of laboratory tests is presented in order to describe possible applications of the method. References Briganti A., Voltaggio M., Tuccimei P. & Soligo M. 2020. Radium in groundwater hosted in porous aquifers: estimation of retardation factor and recoil rate constant by using NAPLs. SN Appl. Sci. 2, 1934 (2020). https://doi.org/10.1007/s42452-020-03610-4 Krishnaswami S., Graustein W.S., Turekian K.K., Dowd J.F. 1982. Radium, thorium and radioactive lead isotopes in groundwaters: application to the in situ determination of adsorption-desorption rate constants and retardation factors. Water Resour. Res. 18:1633–1675.

Radon (222Rn) is a natural radioactive gas formed in rocks and soil by the decay of its parent nuclide (238-Uranium). The rate at which radon migrates to the surface, be it along faults or directly emanated from shallow soil, represents the Geogenic Radon Potential (GRP) of an area. Considering that the GRP is often linked to indoor radon risk levels, we have conducted multi-disciplinary research to: (i) define local GRPs and investigate their relationship with associated indoor Rn levels; (ii) evaluate inhaled radiation dosages and the associated risk to the inhabitants; and (iii) define radon priority areas (RPAs) as required by the Directive 2013/59/Euratom. In the framework of the EU-funded LIFE-Respire project, a large amount of data (radionuclide content, soil gas samples, terrestrial gamma, indoor radon) was collected from three municipalities located in different volcanic districts of the Lazio region (central Italy) that are characterised by low to high GRP. Results highlight the positive correlation between the radionuclide content of the outcropping rocks, the soil Rn concentrations and the presence of high indoor Rn values in areas with medium to high GRP. Data confirm that the Cimini–Vicani area has inhalation dosages that are higher than the reference value of 10 mSv/y.

In the frame of Radon rEal time monitoring System and Proactive Indoor Remediation (RESPIRE), a LIFE 2016 project funded by the European Commission, the contribution of building materials of volcanic origin to indoor radon concentration was investigated. First, total gamma radiation and related outdoor dose rates of geological materials in the Caprarola area (Central Italy) were measured to define main sources of radiation. Second, 222 Rn and 220 Rn exhalation rates of these rocks used as building materials were measured using an accumulation chamber connected in a closed loop with a RAD7 radon monitor. Among others, the very porous “Tufo di Gallese” ignimbrite provided the highest values. This material was then used to construct a scale model room of 62 cm × 50 cm × 35 cm (inner length × width × height, respectively) to assess experimental radon and thoron activity concentration at equilibrium and study the effects of climatic conditions and different coatings on radon levels. A first test was carried out at ambient temperature to determine experimental 222Rn and 220 Rn equilibrium activities in the model room, not covered with plaster or other coating materials. Experimental 222 Rn equilibrium was recorded in just two days demonstrating that the room “breaths”, exchanging air with the outdoor environment. This determines a dilution of indoor radon concentration. Other experiments showed that inner covers (such as plasterboard and different kinds of paints) partially influence 222 Rn but entirely cut the short-lived 220 Rn. Finally, decreases in ambient temperature reduce radon exhalation from building material and, in turn, indoor activity concentration.

In extensional continental settings, crustal-scale normal faults can accommodate deformation and subsidence at their hanging wall via activation and deactivation of subsidiary tectonic structures. Geological data obtained from subsidiary structures are required to infer the position of the tectonic deformation during the spatial-temporal evolution of the growth-fault system, with significant implications for structures belonging to seismogenic settings. Here, we describe a subsidiary tectonic structure (the Amatrice Fault System) accommodating Quaternary extensional deformation in the Amatrice Basin (central Apennines, Italy), which is an intermountain morpho-structural depression involved by the 2016–2017 seismic sequence. Structurally, the Amatrice Fault System defines a ∼10 km-long tectonic feature running through the Amatrice Basin, and consists of NNW-SSE-striking and E-W-striking fault segments that interact and link over time. Cross-cutting fault relationships are used to reconstruct a kinematic scenario of fault growth and propagation under an ENE-WSW-directed crustal stretching, consistent with the paleostress regime governing the Quaternary activity of the central Apennines. The analysis of stable carbon and oxygen isotopes on syn-kinematic carbonate mineralizations (calcite veins and calcite fibers on fault surfaces) indicates a meteoric water circulation during the development of the growing fault structure, characterized by variable contributions of organic carbon (soil CO2), and suggesting surface rupture and hydrodynamic interconnection with the vadose zone during faulting. Geochronological U-Th dating on the same mineralizations indicates Middle-Late Pleistocene ages for the main phase of tectonic activity of the Amatrice Fault System, with the younger age being 108 ± 10 ka. To date, we cannot exclude minor activations of the Amatrice Fault System during the Holocene. Our results shed light on the Pleistocene tectonics in the Amatrice Basin, in which the Amatrice Fault System records fault growth, hydrodynamic regime and structural permeability network developed under possible coseismic conditions. The evolution of minor tectonic structures, such as the Amatrice Fault System, can provide insights on the localization of tectonic deformation at the hanging wall of a master fault, with implication on the releasing seismogenic potential in active tectonic domains similar to the central Apennines.

A buried travertine deposit, identified in a well at Prima Porta (to the north west of Rome, Italy), was investigated using a multidisciplinary approach that included stable isotope geochemistry, mineralogy, petrography and radiometric dating. The travertine body is located just along the western boundary of the Tiber valley, a morpho-tectonic depression of extensional origin; it is associated with the rise of a deep-seated, hypothermal, saline, CO2-rich fluid. The depositional environment was inferred by the macroscopic features of core and microfacies analysis, which suggested that travertine deposition was associated with a low to moderate energy environment, such as gently-dipping, shallow pools on low-angle, terraced slopes. A hydrothermal system, characterised by long circulation paths at depth, and deeply derived CO2-dominated fluids, are supported by geochemical analyses. According to radiometric dating, travertine deposition occurred from between 53.5 +/- 10 ka to 24.2 +/- 4.7 ka; the activation of the travertine-depositing spring was probably coeval with the wettest climatic conditions occurring during MIS3, whereas the end of deposition coincides with the cold and arid phase of the last glacial maximum.

A new method for estimating retardation factor and recoil constant of radium isotopes in groundwater hosted in porous aquifers is described. The method is based on the evidence that alpha-recoiled radium ions, supplied by thorium parent atoms which occur in phases immersed in NAPL (Non-Aqueous Phase Liquids), are not adsorbed on solid phases. Experimental evidence is given that manganese dioxide, zeolite 4A, natural clay, monazite and weathered volcanic rock, all phases normally adsorbing radium from aqueous solutions, when immersed in NAPL adsorb negligible amounts of radium. This allows using experimental data on rock samples, representative of porous aquifers, for estimating Ra retardation factor and its alpha recoil constant in groundwater, without using Rn data as a comparison term. Unlike estimation of retardation factor between the "NAPL method" and the method based on comparison with radon depends on the different process of entry from aquifer rock into groundwater for radon and radium. Precise estimates of retardation factor and recoil constants of radium allow to apply equations ruling the temporal evolution of radium isotopes in groundwater and to determine its age. Implications, useful for measuring the contamination age of soils by NAPL fluids, are described as well.

About 15 years ago, a fuelling station in Roma (Italy) was dismissed. When underground tanks were removed, a subsoil NAPL (Non-Aqueous Phase Liquid) contamination came out, showing gasoline leakage from the reservoirs. Monitoring actions took place next and only recently radon dissolved in groundwater was measured for a year and used as tracer of NAPLs in view of its high solubility in these substances. The relative deficit of radon in polluted groundwater compared to radon in background “clean” water allowed us to detect areas where residual gasoline is still located. The source of pollution was identified in correspondence of former gasoline tanks, in agreement with direct measurements of dissolved NAPLs, mainly Methyl Tertiary Butyl Ether (MTBE), a resistant and water-soluble additive introduced in gasoline in place of lead. A short and transient plume of MTBE was occasionally recognized. We hypothesize that the rise of groundwater table enhances removal of MTBE, likely adsorbed onto soil minerals such as zeolites, thus increasing its concentration in water. MTBE levels are then progressively reduced by natural attenuation processes, with half-life of about 23 days. Estimates of MTBE saturation from radon-deficit equations were not reliable because the aquifer is not homogeneous in terms of 226Ra distribution, porosity and emanation power and no equilibrium is reached for radon partitioning between NAPL and water.

Nowadays, the access to drinkable water becomes more and more difficult for many regions around the world and the highland of Antananarivo, Madagascar, does not escape this problem. The groundwater resources of Antananarivo region could be a solution to consider for water needs, especially during drought. Knowing the groundwater age permits to estimate the aquifer potentiality, to predict the sustainability if the water source is health safe, and then to help the decision maker for the best management of the groundwater resources. Radium isotopes in the groundwater of this area have been measured to estimate the residence time of the water in these shallow aquifers. The analyses were carried out by using high resolution gamma spectrometry on MnO2-impregnated fibers as radium collectors from groundwater. Ra-226 activity ranges from 29.2 +/- 10.2 to 241.7 +/- 26.9 mBq/L-1 and Ra-228 activity ranges from 22.5 +/- 4.9 to 684.9 +/- 13.5 mBqL(-1) whereas Ra-228/Ra-226 activity ratio ranges between 0.20 +/- 0.05 and 4.86 +/- 0.88. Three variations of a same basic model depending on the variation of Ra-228/Ra-226 activity ratio in function of alpha-recoil, dissolution, adsorption and time were used to estimate the groundwater residence time. The most reliable ages of the highlands' groundwater, calculated in this way, range from 0.2 to 10 years. According to these results, the groundwater of the E-NE sector of the area have the highest average residence time of 6.5 years and a total potential volume of available groundwater estimated to about 152. 10(6)m(3). These features, coupled with radium content below the WHO guidance levels for drinking water, show that the groundwater of this sector constitute a reliable resource to supply the region of its needs for human as well as for agricultural purposes.

A detailed geochemical study on radon related to local geology was carried out in the municipality of Celleno, a little settlement located in the eastern border of the Quaternary Vulsini volcanic district (central Italy). This study included soil-gas and terrestrial gamma dose rate survey, laboratory analyses of natural radionuclides (238U, 226Ra, 232Th, 40K) activity in rocks and soil samples, and indoor radon measurements carried out in selected private and public dwellings. Soil-gas radon and carbon dioxide concentrations range from 6 to 253 kBq/m3 and from 0.3 to11% v/v, respectively. Samples collected from outcropping volcanic and sedimentary rocks highlight: significant concentrations of 238U, 226Ra and 40K for lavas (151, 150 and 1587 Bq/kg, respectively), low concentrations for tuffs (126, 123 and 987 Bq/kg, respectively), and relatively low for sedimentary rocks (108, 109 and 662 Bq/kg, respectively). Terrestrial gamma dose rate values range between 0.130 and 0.417 μSv/h, being in good accordance with the different bedrock types. Indoor radon activity ranges from 162 to 1044 Bq/m3; the calculated values of the annual effective dose varied from 4.08 and 26.31 mSv/y. Empirical Bayesian Kriging Regression (EBKR) was used to develop the Geogenic Radon Potential (GRP) map. EBKR provided accurate predictions of data on a local scale developing a spatial regression model in which soil-gas radon concentrations were considered as the response variable; several proxy variables, derived from geological, topographic and geochemical data, were used as predictors. Risk prediction map for indoor radon was tentatively produced using the Gaussian Geostatistical Simulation and a soil-indoor transfer factor was defined for a 'standard' dwelling (i.e., a dwelling with well-defined construction properties). This approach could be successfully used in the case of homogeneous building characteristics and territory with uniform geological characteristics.