2013 NGWA Summit — The National and International Conference on Groundwater

LNAPL In Situ Recovery in Low Permeability Soil Using Soil Washing and Multi-Phase Vacuum Extraction

Tuesday, April 30, 2013: 1:35 p.m.
Regency West 6 (Hyatt Regency San Antonio)
Thomas Robert, Institut national de la recherche scientifique
Richard Martel, Ph.D., Institut national de la recherche scientifique
Rene Lefebvre, Institut national de la recherche scientifique
Jean-Marc Lauzon, TechnoRem Inc

A multi-phase vacuum extraction system is used for LNAPL recovery at an industrial site consisting of a heterogeneous urban fill. The system shows limitations due to particular soil properties: low permeability soil layers (K < 10-6 m/s), high content in organic matter (foc =1.6%), carbonate minerals (up to 30%-mass), and high water retention in the dewatered horizon. A research project was carried out to use soil washing to improve overall LNAPL recovery of the vacuum extraction system, through three potential application scenarios. The first application consisted in the use of a low-concentration surfactant solutions (<0.5%-mass) to improve water drainage in the dewatered horizon by lowering the water surface tension by 50%. However, the use of two types of surfactants did not modify the shape of the soil water retention curve, suggesting that water was retained by forces other than capillarity, such as adsorption. The second scenario consisted in the use of a low-concentration surfactant solution (<0.5%-mass) to enhance the mobility of free-LNAPL phase and residual LNAPL trapped in the saturated zone by lowering the LNAPL-pore fluid interfacial tension (IFT) by a factor of 200. However, a field pilot test showed that even with such an IFT reduction, capillary forces controlling LNAPL trapping remained higher than the viscous and gravitational forces acting to displace them. The in situ increase of viscous forces during soil washing was limited by the unconfined nature of the aquifer. Finally, a third scenario involving miscible flooding with a high concentration alcohol solution was tested inside a 3D physical model (4 m3 sand box) simulating a 5-spot injection/extraction pattern. Results indicated that miscible flooding is possible for that site, even though improvements of the sweep efficiency of the alcohol solution using a mobility control technique (such as a polymer) would be required prior to a field application.

Thomas Robert , Institut national de la recherche scientifique
Thomas Robert is a Ph.D. candidate at the Institut National de la Recherche Scientifique in Quebec City. He has six years of experience working for a site remediation and environmental consulting firm as a project manager and hydrogeologist.

Richard Martel, Ph.D. , Institut national de la recherche scientifique
Professor Richard Martel research focuses on the development of novel in situ soil and groundwater remediation technologies, as well as aquifer characterization and management. His work is centered around laboratory and field work.

Rene Lefebvre , Institut national de la recherche scientifique
Rene Lefebvre is Professor in hydrogeology at the Institut national de la recherche scientifique (Centre Eau Terre Environnement) in Quebec City. He has degrees in geological engineering, geochemistry and hydrogeology, and expertise on multiphase transfer processes involving geochemical reactions in geological media. He has carried out major regional aquifer assessment projects aiming to improve groundwater management and protection in Canada and abroad. His research also aims to improve aquifer characterization by developing more representative flow and transport numerical models of heterogeneous local or regional systems, notably with the use of cone penetration soundings and surface geophysics.

Jean-Marc Lauzon , TechnoRem Inc
Jean-Marc Lauzon is the president of TechnoRem. TechnoRem employs some 20 engineers and technicians specializing in hydrogeology, geology, geography, civil engineering, process engineering, geochemistry, mathematical modelling, environment and site decontamination.