Hydrocarbon Plume Attenuation Monitoring with Electrical Methods

In the framework of a research programme on natural attenuation of hydrocarbon and chlorinated solvents, geophysical methods have been evaluated for pollutant plume evolution monitoring in ground water. Test site is an ancient cokery plant where 2 large leaking coal tars have polluted ground water since decades. Hydrocarbon plume which is mainly composed of dense (DNAPL) coal tars, few light (LNAPL) hydrocarbon compounds with sulphate and nitrate which are by-products of coal refinery. Ground water table is situated around 25 to 30 m deep. Clay aquitard is around 60 m deep above the chalk aquifer. <br>Since 3 years, pollutant plume is monitored with a buried electrode configuration (resistivity and chargeability and electrical tomography profiles. Surface geophysical measurements are compared to chemical analysis (anions, cations, total hydrocarbon, and polycyclic aromatic hydrocarbons) and physical-chemical parameters (pH, Eh, conductivity) loggings in boreholes. <br>As hydrocarbon biodegradation strongly modifies electrical properties in soils and in ground water, hydrocarbon DNAPLs are characterized by conductive plumes. Geophysics showed agriculture water pumping and chalk fracturing influence on plume migration. The good correlation between chemical and geophysical parameters proves that electrical methods are effective for hydrocarbon plume monitoring and long term plume modelling.