Lab scale experiment assessment of air sparging BTEX removal in fine grained aquifer of Shiraz Oil Refinery

Abstract

Groundwater contamination by petroleum hydrocarbons is a major concern throughout the world. Shiraz Oil Refinery (SOR) site has been subjected to several leakage and spills in the past, and consequently six separate non-aqueous phase liquids sources and their consequent plumes are formed in the fine-grained Quaternary aquifer of the site. Laboratory experiments were performed to study the benzene, toluene, ethyl-benzene, and the three xylene isomers (termed BTEX) removal efficiency of air sparging (AS) method, using a site porous material in a three-dimensional flow box model. Different air injection flow rate and injection patterns in four different set of experiments were examined. Water level change (upwelling), dissolved oxygen (DO) values as indirect indicator of sparging well radius of influence (ROI) and BTEX concentration of the saturated zone as direct indicator were measured in a dense network of monitoring wells installed in the porous material section. Results showed that channelized airflow is more probable, resulting in reduction of the effectiveness of the AS in the SOR finegrained aquifer. To apply AS method in this media, decreasing AS flow rate but increasing sparging points is a more efficient strategy during AS operation. Furthermore, special consideration should be taken in determining ROI in fine-grained porous material due to channelization of airflow. Therefore, a proper design of number and placement of the sparging points and monitoring wells are required. Therefore, AS remediation method is effective to reduce BTEX concentration in fine-grained material of SOR aquifer if well designed and operated.