Grandia, Fidel

Diffusive gradients in thin fi lms (DGT) have been tested in CO2-rich, metal-bearing fl uids from springs in the Campo de Calatrava region in Central Spain, to assess their applicability as a monitoring tool in onshore CO2 storage projects. These fi lms are capable of adsorbing metals and recording changes in their concentration in water, sediments, and soils. Considering that CO2 dissolution promotes metal solubilization and transport, the use of these fi lms could be valuable as a monitoring tool of early leakage. A number of DGT have been deployed in selected springs with constant metal concentration. The studied waters show high concentrations of Fe, as high as 1 × 104 μg·L–1, Ni, Co, Zn, Cu, and Mn. Comparing re-calculated metal concentration in DGT with metal water concentration, two different metal behaviors are observed: (i) metals with sorption consistent with the metal concentration (i.e. plotting close to the 1:1 line in a [Me]DGT: [Me]water plot), and (ii) metals with non–linear sorption, with some data showing metal enrichment in DGT compared with the concentration in water. Metals in the fi rst group include Fe, Mn, Co, Ni, and U, and metals in the second group are Zn, Pb, Cr, Cu, and Al. From this research, it is concluded that the metals in the fi rst group can be used to monitor potential leakage by using DGT, providing effective leakage detection even considering low variations of concentrations, episodic metal release, and reducing costs compared with conventional, periodic water sampling.

Carbon dioxide is a gas denser than air, and its point-source ground emission from natural systems or from areas impacted by CO2 injection underground may result in hazardous accumulation, especially in topographically-depressed sites. The use of atmospheric dispersion numerical models helps predicting the dispersion of the CO2-enriched gas plume once emitted from underground and allows an accurate map of hazard level through time under particular meteorological conditions. In this study, the accuracy of atmospheric dispersion simulations has been tested using a natural system of CO2 emission to atmosphere from underground in an area called Solforata di Pomezia, near the city of Rome in central Italy. This area is located in the Alban Hills, which underwent volcanic activity during the Quaternary, and is characterised by low permeability volcanic and sedimentary formations that allow the accumulation of gas at shallow depths and below surface. This site has been long investigated in terms of soil CO2 emission rates, which range from 44 to 95 ton∙day-1. Using the TWODEE2 numerical code, a number of simulations were performed considering a set of combined CO2 soil flux emission and meteorological (wind, temperature) from literature. The results fit well in the range of measured CO2 concentration in air at distinct heights in the site. The model does not predict lethal gas concentration at heights 1 and 2 m above the ground based on actual soil emission rate (95 ton∙day-1). Two probabilistic models were developed with emission rate five (500 ton∙day-1) and ten (1000 ton∙day-1 times bigger than nowadays but still no hazardous levels were predicted.

This study presents the experimental and modeling results of CO 2 injection and transport in the vadose zone performed in PISCO2 facilities at the ES.CO2 center in Ponferrada (North Spain). During 46 days of experiments, 62.10 kg of CO 2 were injected through 16 micro-injectors in a 35 m 3 experimental unit fi lled with sandy material. Monitoring and mapping of surface CO 2 fl ux were performed periodically to assess the evolution of CO 2 migration through the soil and to the atmosphere. Numerical simulations were run using TOUGH2 code with EOS7CA research module considering two phases (gas and liquid) and three components (H 2 O, CO 2 , air). Two layers (sand, gravel) and atmosphere boundary were implemented taking into account heterogeneous soils, homogeneous soil, rainfall, temperature, and liquid saturation to allow a better understanding of CO 2 behavior in the vadose zone. This combined experimental and modeling approach shows that CO 2 leakage in the vadose zone quickly comes out through preferential migration pathways and spots with the ranges of fl uxes in the ground/surface interface from 2.5 to 600 g·m −2 ·day −1 . This gas channeling is mainly related to soil compaction and climatic perturbation. This has signifi cant implications for designadapted detection and monitoring strategies of early leakage in commercial CO 2 storage.

Carbon dioxide is an essential gas for life on earth although it can be lethal to living beings at high concentrations in the atmosphere. Episodic release of CO2 from underground can occur either from natural processes (i.e., mantle degassing, thermal decarbonation) or industrial (geological storage of CO2, CCS). CO2 is a colourless and odourless gas denser than air, and once released in the atmosphere from point sources, its dynamics is initially governed by buoyancy and a gas cloud can accumulate above the ground (gravitational phase) leading to the formation of the so-called “CO2 lakes”. With time, CO2 distribution is then governed by wind and atmospheric turbulence (passive dispersion phase). Natural analogues provide evidences of the impact of CO2 leakage on vegetal cover, wild life and human beings. In this work, the dynamics of CO2 in the atmosphere after ground emission is assessed to quantify their potential risk. Two approaches have been followed: (1) direct measurement of air concentration in a natural emission site, where formation of a “CO2 lake” is common and (2) numerical atmospheric modelling with the TWODEE code. The studied site is located in the Campo de Calatrava region in central Spain, which is known for a widespread degassing of mantle-derived CO2. This site, called Cañada Real, has a degassing rate between 1 and 3 tonnes of CO2 per day. When atmospheric conditions are quite stable, i.e., negligible wind speed, the formation of a blanket of CO2-enriched air is visible at naked eye reaching up to 50 cm high. The CO2 concentration measured in air is typically higher than 10,000 ppm in most monitoring stations. The measured data are consistent with the numerical models that predict maximum concentration between 40,000 and 70,000 ppm CO2 in air, which is by far higher than the 30,000 ppm threshold from which hazardous effects on human beings are observed. Conclusions from this work, however, indicate that the risk for humans even at large emission rates is low due to the CO2 dispersion effect into the atmosphere, and only under very particular conditions lethal effects are predicted.