Multiphase Flow Fields in In-situ Air Sparging and its Effect on Remediation

Abstract

In-situ air sparging (IAS) is used for the clean-up of soil and groundwater that are contaminated with volatile organic compounds in relatively permeable subsurface environments. In this study, we investigated the secondary groundwater and gas flow fields that develop in the vicinity of single and multiple air sparging wells. The purpose is to evaluate their effects on contaminant plume migration and thus, remediation. Governing equations describing multiphase flow and contaminant transport in a three-dimensional domain were formulated and solved using the Galerkin finite element technique. Trichloroethylene was selected as a target contaminant. The increase in air injection contributed to an increase in the size of the IAS cone of influence and the gas saturation levels within the cone. This reduced the groundwater velocity within the cone and increased the zone of detour of groundwater around the air sparging wells. This outcome was quantified and compared under several IAS operations. Different soil permeability characteristics also affected the groundwater and gas flow patterns, and this impacted the remedial performance of the IAS system. Under high ambient groundwater velocity, an air sparging system that uses a single injection well caused the detour of contaminant plumes around injection wells, regardless of air injection rates, and failed to meet the remedial goal specified here. This system was successful for relatively low ambient groundwater velocity environments used here. An IAS system with multiple injection wells was effective in capturing and remediating the detoured contaminant plume, and showed superior performance when compared to a single injection well IAS system. Using IAS simulation, we also analyzed the impact of injection rates on site remediation using single or multiple wells. Design criteria that are based on the results of this study would be useful in enhancing the performance of the IAS systems.

Interphase mass transfer between fluids in subsurface formations: A review

“…The reasons for unstable movement of air are discussed in more detail in Section 3.4.3. A part from that air sparging can lead to decrease in relative permeability of the groundwater at the injection region in case of a moving contaminant plume [139]. The system under consideration in the above cited works relating to NAPL recovery was entrapped NAPL (in form of pools and entrapped blobs) in water saturated porous medium, meaning that the interphase mass transfer occurred from both the air-water interface and the air-NAPL interface.…”

In-Situ Remediation Approaches for the Management of Contaminated Sites: A Comprehensive Overview

“…Rahbeh and Mohtar ( 2007 ) studied the positive effect of multi-phase transport models to full-scale treatment by air sparging and SVE of BTEX-contaminated site. A similar fi eld study envisaging the success of air sparging with MPE was done by Jang and Aral ( 2009 ).…”

“…An in -situ air sparging system with multiple injection wells performed better than a single injection well in -situ air sparging system and was effective in capturing and remediating the detoured contaminant plume (Jang and Aral 2009 ). At fi eldscale, Kao et al ( 2008 ) showed >70 % BTEX removal within 20 months at an average groundwater temperature of 18 °C through the biosparging system.…”

Fluids’ dynamics in transient air sparging of a heterogeneous unconfined aquifer

“…One-phase sharp-interface model requires an intrinsic permeability and porosity as the only parameters and assumes a distinct free boundary between the air plume and groundwater (Nikolskii 1961). Two-three phase flow models consider combined air and groundwater (and sometimes NAPL) motion (McCray and Falta 1996;Mei et al 2002;Jang and Aral 2009) that requires phase permeabilities and capillary pressure functions, which are difficult to measure in the field. Any intermittency of AS-SVE-as in our case-involves imbibition-drainage cycles.…”