Joint research project

Geophysical techniques for monitoring hydrocarbon contamination phenomena using laboratory experiments

Project leaders
Enzo Rizzo, Mohamed Sayedgomaa
Agreement
EGITTO - ASRT - Academy of Scientific Research and Technology
Call
CNR-ASRT 2016-2017
Department
Earth system science and environmental technologies
Thematic area
Earth system science and environmental technologies
Status of the project
New

Research proposal

The shallow subsurface of the Earth is an extremely important geological zone that yields much of our water resources, supports our agriculture and ecosystems, and influences our climate. However in the last two centuries, the expansion of industrial and agricultural activities has caused an exponential growth of contaminant and pollutant introduced in this system. At the present, the environmental problem of soils and groundwater pollution (for both natural and anthropogenic reasons) affects approximately twenty million square Km of the Earth's surface and the polluted area is increasing by 1% per year. One of the most important impact is groundwater contamination and related human health problems; major concerns are the long time needed to regenerate contaminated soil and the considerable investment required for remedial measures (Van-Camp et al., 2004). The Italian situation is in line with that of Europe, with more than 5 million Euro just for the remediation of 1250 priority sites. Moreover, in the South of Italy, the degradation of soil and groundwater is particularly heavy for the presence of official landfill and numerous abandoned industrial sites. It is even more, due to the presence of occult illegal dumping (only partly surveyed) of toxic waste and often harmful products elsewhere. One of the most significant sources of the subsurface contaminants, which is attributable to human activities, is associated to petroleum products for example coming from industrial disasters, leaking underground storage tanks or oil well blow out. This type of contamination is a heavy environmental problem because infiltrated oil can persist in the ground for a long time. The hydrocarbons (NAPLs) leach into the soil, eventually releasing volatile gas phase components that can reach the atmosphere spreading through the porosity of the soil. Once reached the saturated zone, NAPLs can conclude the vertical motion or continue it within the aquifer, depending on its density is respectively less (LNAPLs) than or greater (DNAPLs) than that of water. In the first case, it will form a lens of pollutant that floats on the surface of the water by following the seasonal variations of level. Accurate field estimate of parameters of contamination are often difficult to obtain by conventional hydraulic and biological methods. These direct methods often provide scarce information (both in time and space) of the aquifer properties especially because drilling a large number of boreholes is both expensive and time-consuming. Furthermore, the numerical modeling for site characterization and flow and transport analysis strongly depends on the density of data availability. In order to overcome these limitations, it should be necessary to develop and use new multidisciplinary approaches introducing also minimally invasive, rapid and cost-effective new techniques, which are sensitive to water saturation, water flow and bioactivity of contaminant, such as the geophysical methods. There has been a growing interest in the use of geophysical methods for the study of soils and groundwater contamination but recent works suggest that the geophysical response at a NAPL contaminated subsurface depend on several complex factors, such as the type, release history, the distribution in the vadose zone or water in the saturated zone, hydrological processes, the saturation history of the contaminated media, and biological processes. Therefore, the proposal activity is focused on the use of geophysical techniques that, with the advantage of rapid deployment and the ability to cover spatially extensive areas at higher density and temporal frequencies, can complement hydrological, biological and geochemical data, in order to obtain more detailed information about the contamination state of subsoil. During the present proposal, more attention will be given to electromagnetic methods, such as Electrical Resistivity Tomography (ERT), Induced Polarization (IP), and ground penetrating radar (GPR). These methods have shown to be sensitive to both the direct presence of contaminants, either in free phase, or adsorbed to the solid matrix and the biological activity fostered particularly by the presence of organic contaminants. Actually, electromagnetic surveys (DC, IP, , GPR) are the most used in the hydrogeological context for the study of pollution because electromagnetic parameters such as electrical conductivity, polarizability, electrical potential, and electrical permittivity are sensitive to the petrophysical and hydrologic properties of soil (porosity, hydraulic conductivity, fluid content, salinity), to the soil texture and structure (grain size, arrangement of the solid parts of the soil and of the pore spaces), and to the water geochemical characteristics (redox potential, electrical conductivity, pH) that can be heavily modified by the presence of contaminants and by biodegradation activity. At now, the integration of hydraulic, geophysical and bio-chemical data sets is a complex process, but this project will try to develop new acquisition approaches and experimental protocols, which will ensure a good repeatability for different contamination status. Therefore, the importance of the project is an improving and breaking barriers of existing polluted subsurface characterization approaches, methods and tools. As a consequence of their improvement and combination, an efficient exploitation of preceding research results will be possible, as well as a powerful tool-set needed for understanding of yet unexplained observed phenomena.

Research goals

This project proposes an integrated geophysical approach focuses mainly on the possibility to get information in a controlled environment, about the distribution of contaminants, from time-lapse geophysical monitoring. However, our current understanding of contaminated subsoil is based in large part on concepts, models, property descriptions and measurement methods that have been developed to interpret and explain observations at a given scale of interest and with a single disciplinary approach. It is nowadays recognized that complex contamination phenomena such as hydrocarbon contaminants could be dealt with various branches of science environment. Therefore, the aim of the project is to model the space and time variability of a contaminated plume and eventually its biodegradation by proposed geophysical characterization methods in an analogue sand-box system in the laboratory. In this context, several challenges which are important for contaminant problems include developing new conceptual understanding and quantitative modeling. The main scientific and technological objectives, involving conceptual, experimental, and modeling aspects, in order to integrate the different geophysical characterization approaches with measurements of contaminant biodegradation activity and to evaluate the potentiality of geophysical techniques to monitor soil hydrocarbon contamination progress.

Last update: 28/03/2024