Surfactant-enhanced air sparging with viscosity control for heterogeneous aquifers

Abstract

The effects of surface-tension and/or viscosity changes in groundwater on the remedial performance of air sparging for heterogeneous aquifers were investigated. The study used a one-dimensional (1-D) column and a two-dimensional (2-D) flow-chamber aquifer model. To introduce a heterogeneous setting, the middle part of the model was packed with a finer soil [LKZ, low hydraulic conductivity (K) zone]. Fluorescein sodium salt was used at 200 mg/L for all experiments as a surrogate contaminant. For the 1-D column experiments, the rate of fluorescence decay in the LKZ during surfactant-enhanced air sparging (SEAS) was significantly higher than during the standard air sparing (AS) process without additives; the area of fluorescence loss, measured after 17 h of air sparging (including ozone), was double and triple that of the conventional AS process, for SEAS without thickener (SEAS1) and SEAS with thickener (SEAS2), respectively. Experimental results using the 2-D chamber also confirmed the enhanced air intrusion into the LKZ during the SEAS process. The air fluxes through the LKZ increased by 47 and 103% for the SEAS1 and SEAS2 compared to AS, respectively; and 79 and 90% of fluorescence disappeared in the LKZ during ozone injection for SEAS1 and SEAS2, respectively, whereas only 10% disappeared for AS during the 3-h experimental period. The findings of this study indicate that the AS process, at low surface tension and increased groundwater viscosity may be a viable alternative to the conventional AS process for aquifers of heterogeneous hydrogeological formations.