To advance the in-situ remediation technology 'air sparging' a consortium was set up consisting of the dutch engineering company 'Oranjewoud', the University of Twente, the Technical University of Delft, Shell, and the regional governments of Friesland and Gelderland. This consortium launched a research project with the objective to develop design rules and sophisticated monitoring methods to make air sparging a more full-fledged remediation technology. To reach this objective the research focusses on modifying retention zones (NAPL zones) into retardation zones (non-NAPL zones) and enlarging the aeroob zone by means of air sparging.
Within the project outlined above the thesis [S. Zwerink, 1998] aimed to clearify the impact of soil permeability and injection rate on transport of dissolved oxygen (DO) in order to derive design rules. Insight in the 'radius of influence' (ROI), in which injected air contributes to biodegradation, is essential in designing air sparging systems. Oxygen partitioning from the gas to the aqueous phase is strongly influenced by imbibition and drainage in porous media. To model the development of DO regions, and to compute average DO concentrations, the STOMP Water-Air operational mode was used in a two-dimensional axisymmetric domain. The domain consisted of more than 1800 nodes creating a 100-m-long and 10-m-deep homogeneous isotropic aquifer. Based on this reference case, simulations have been performed classified in three categories i.e.: isotropic permeability, anisotropic permeability and injection rate. Impact of differences in parameter values among the computations were monitored by means of: DO concentration, gas saturation, gas pressure and water table mounting. Since DO concentrations cannot directly be calculated these have been computed by multiplying dissolved air concentrations and the DO-dissolved air mass fraction under ambience conditions. Results from the STOMP simulator have been transposed into contour plots and time dependent diagrams ready for interpretation. The images included in this poster paper demonstrate the process of injecting air and the consequences to the DO region due to oxygen partioning from the gas phase. The computations have lead to usefull relations for the ROI based on soil and design characteristics.
Zwerink, S., 1998. Modelling of air sparging in water saturated soils; a theoretical research to determine the aerobic zone in order to derive design rules. Ph.D. dissertation, University of Twente, Enschede, The Netherlands. (language: Dutch)