In situ stimulation and remediation of contaminated fractured soils
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies - Ia: Extraction & Remediation (T1-4a)
Keywords: contaminated soil, remediation, hydraulic fracturing, steam injection, bio-ventilation
K.E. Klint 1, B. Nilsson 1, W. Slack 2, T. Broeker 3, T. Kasela 4, M. Jeczalik 4, F. Haessler 5, Y. Benoit 5, Ph. DeLaplace 5, D. Tzovolou 6, C. Aggelopoulos 6, C.D. Tsakiroglou 6,*
1 Geological Survey of Denmark and Greenland, Copenhagen, Denmark
2 Frx, Inc., Cincinnatti, OH, USA
3 Broeker Drilling Company, Holbaek, Denmark
4 Hydrogeotechnika Ltd, Kielce, Poland
5 Institut Francais du Petrole, Rueil-Malmaison, France
6 Foundation for Research and Technology, Patras, Greece
ABSTRACT
Fractured and low permeable sediments / soils comprise a major part of the subsurface especially in Northern and Central Europe. In these soils, the spreading of non-aqueous phase liquids (NAPLs) toward underground aquifers is due to the fractures that form hydraulic avenues through an otherwise low permeable porous matrix. Traditional remediation technologies applied to permeable soils (e.g. free-product recovery, soil vapor extraction, bioremediation, steam injection, etc.) are primarily based on the installation of vertical wells in the subsurface. However, in a fractured unsaturated zone where the permeability of the porous matrix is very low, the NAPL transport pathways are controlled by vertical fractures and wells, and target contaminants that have been accumulated in the matrix porosity may be bypassed. Therefore, any remediation method that is based on such wells is expected to be very inefficient. An effective in situ remediation of a fractured and contaminated site could be done if the horizontal hydraulic conductivity was increased by stimulating the subsurface with hydraulic fracturing. The goal of the present work is the development of scientifically supported criteria for the selection of the most efficient stimulation set-up and remediation strategy to cleanup the NAPL-contaminated unsaturated zone of fractured and low permeable soils. The test site is the abandoned Kluczewo military airport, which is situated in North Poland, and is the second largest groundwater environment contaminated by jet fuel during a long period (1927-1992). The detailed geological characterization of the site revealed that the unsaturated zone is a highly heterogeneous fractured porous medium consisting of five zones (units). The transport properties of the soil matrix and tectonic / desiccation fractures were determined by combining lab-scale experimental techniques with theoretical modelling. Before initiating remediation, the chemical characterization of the site, was carried out by analyzing in situ and ex situ, a great number of soil and water samples, with the use of a variety of chromatographic techniques (PollutEval, GC-FID, GC-MS, etc). Hydraulic fractures were installed and tested on five highly contaminated areas (cells). Two remediation technologies were selected and implemented on the site: (i) thermal treatment by injecting steam for a short period of time, and (ii) bio-ventilation by injecting and/or extracting air for a long period of time. Information concerning the geology of the area and the up-scaled multiphase transport properties of the various units was utilized to simulate the two remediation scenarios. The efficiency of each remediation scenario was monitored by detecting the total concentration and composition of hydrocarbons remaining in the soil. Such information was also used to calibrate the numerical simulators. Finally, a cost benefit analysis enabled us to assess the feasibility of the approach used.
Presented Wednesday 19, 11:00 to 11:18, in session Sustainable & Clean Technologies - Ia:Extraction-Remediation (T1-4a).
