A multi-statistical approach for estimating the total output of CO2 from diffuse soil degassing by the accumulation chamber method.

CO2flux measurements at the soil-atmosphere interface are commonly carried out as part of site char-acterization in areas elected for CO2geological storage purposes. This approach represents an importantmonitoring tool to detect and quantify leakages during operational and post-operational stages relatedto the injection of anthropogenic CO2.A large variety of techniques to measure diffuse CO2soil flux is available and one of the most widelyused is the accumulation chamber method. With this method, the total output is statistically estimatedafter measuring the CO2flux in selected points of a certain area. Several statistical approaches can beapplied and it is important to select the most representative and significant procedure. Consequently,in this paper six different methods were used to calculate the total CO2output, as follows: arithmeticmean, minimum variances unbiased estimator, bootstrap resample, partitioning of data into differentpopulations with graphical and maximum likelihood procedures, and sequential Gaussian simulation.Eight campaigns were carried out in the Hontomín CO2Storage Technology Development Plant (Bur-gos, Spain) and in natural analogs of CO2storage (Campo de Calatrava, Spain and Mt. Amiata, CapreseMichelangelo and La Solfatara, Italy). Our results showed that sequential Gaussian simulation is the mostprecise method for evaluating the total CO2output and the respective confidence interval. Neverthe-less, the estimation of the total CO2output with other statistical methodologies allowed to develop anapplication procedure for choosing the most reliable and realistic approach.