"Radon deficit technique’s variability in a DNAPL contaminated site: a spatio-temporal approach"

Uncontrolled landfill sites are one of the main sources of underground and surface water contamination. The absence of monitoring leads to the leakage of leachates into the environment, thereby severely contaminating the aquifers of the area. That is what happened in Sardas landfill located close to Sabiñanigo (Huesca, Spain). It is an old uncontrolled landfill that has been dumping huge quantities of urban, agriculture and industrial wastes since the 70s. Among all the waste residues in Sardas, the most toxic are the leachates of chloro-alkyl industry and the organochlorides generated by the pesticides industry. Inquinosa produced lindane from 1975 to 1988 and formulated lindane products until 1992. The disposal of waste generated a flooded area of DNAPL (Dense NonAqueous Phase Liquids) above the impermeable marl layer, composed by a mixture of HCHs, Chlorobenzenes, BTEX and other chlorinated compounds, which spread downstream the dump, imply a great threat for soil, surface water and groundwater quality, as for human health and ecosystems. As a persistent organic pollutants contaminated macro-site, Sardas became a very interesting heterogeneous site to study, and presents suitable conditions to assess whether non-invasive screening techniques as the Radon deficit technique are applicable at the site. The Radon deficit technique use the natural presence of Radon (Rn) in soil and its strong affinity to organic fluids relative to water. In correspondence of the contamination a decrease of the Rn signal on the surface would be seen. This technique was successfully tested in homogeneous contaminated sites by LNAPL and DNAPL. It was also assessed for the Inquinosa industrial site. With the objective to find which conditions influence the measurement of Radon, and if it’s possible to determine a relationship between the Rn deficit peaks and the contamination, the current work analyzes data from four different campaigns, lasting from 2017 to 2019. The results of ANOVA test have shown that the only atmospheric condition that influence the measurement of Radon is Temperature. A spatial interpolation of data has been carried out for contaminants in water and HCHs in soil at different depths. A significative Pearson correlation between Rn signal and contaminants was found on the software R studio. On the other hand, with the software ArcGIS was possible to build a better representation of the comparison between Rn signal and the contamination. The results of Sardas site show that there is a relationship between the decrease of Rn signal and contaminants in water and HCHs in soil. Results also allow to say that Rn deficit technique is applicable, as long as many measurements are made for each sampling point, if the temperature is almost constant, and the covered sampling area is sufficiently extent.