: The U.S. Environmental Protection Agency (EPA) Engineering Issue Papers are a series of technology transfer documents that summarize the latest available information on specific technical issues, including fate and transport, specific contaminants, selected treatment and site remediation technologies, and related other issues. This Engineering Issue Paper is intended to provide remedial project managers (RPMs), on-scene coordinators (OSCs), contractors, and other state, industry, or private remediation managers with information to assist in the evaluation and possible selection of appropriate in-situ chemical oxidation (ISCO) remedial alternatives. This Engineering Issue Paper provides an up-to-date overview of ISCO remediation technology and fundamentals, and is developed based on peer-reviewed literature, EPA reports, web sources, current research, conference proceedings, and other pertinent information.

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In-Situ Chemical Oxidation

Simulation and optimization technologies for petroleum waste management and remediation process control

Defining the air sparging radius of influence for groundwater remediation

The injection of gases into liquid saturated porous media is of theoretical and practical interest (e.g., air sparging for the removal of volatile organic compounds from contaminated aquifer sediments). The influence of the rate of gas delivery and the vertical distance from the source are developed. The concept of a “near-injection region” is presented in which the pressure gradients exceed buoyant gradients and thus exhibits largely radial flow. The near-injection size is shown to have an area required to carry the injected gas flow under unit gradient. The parabolic movement of gas outside of this area which has often been observed is explained as reflecting the sum of many realizations of gas channels following random lateral movements as they precede upward independent of flux. These concepts are confirmed through comparison with published and experimental data of air injection into slabs consisting of saturated sands of a range of textures.

The Local Geometry of Gas Injection into Saturated Homogeneous Porous Media

Interphase mass transfer between fluids in subsurface formations: A review

Air sparging has been used for several years as an in situ technique for removing volatile compounds from contaminated ground water, but few studies have been completed to quantify the extent of remediation. To gain knowledge of the air flow and water behavior around air injection wells, laboratory tests and model simulations were completed at three injection flow rates (62, 187, and 283 lpm) in a cylindrical reactor (diameter - 1.2 m, depth = 0.65 m). Measurements of the air flux distribution were made across the surface of the reactor at 24 monitoring locations, six radial positions equally spaced along two orthogonal transects. Simulations using a multiphase flow model called T2VOC were completed for a homogeneous, axisymmetric configuration. Input parameters were independently measured soil properties. In all the experiments, about 75 percent of the flow injected exited the water table within 30 cm of the sparge well. Predictions with T2VOC showed the same. The averages of four flux measurements at a particular distance from the sparge well compare satisfactorily with T2VOC predictions. Measured flux values at a given radius varied by more than a factor of two, but the averages were consistent between experiments and agreed well with T2VOC simulations. The T2VOC prediction of the radial extent of sparging coincided with the distance out to which air flow from the sparge well could not be detected in the reactor. The sparging pattern was relatively unaffected by the air injection rate over the range of conditions studied. Changes in the injection rate resulted in nearly proportional changes in flux rates.

Three‐Dimensional Experimental Testing of a Two‐Phase Flow‐Modeling Approach for Air Sparging

Air sparging is a technology for removing dissolved and volatile phase chemicals (VOCs) from the saturated zone. It is used in conjunction with soil vapor extraction (SVE) and sometimes pump and treat systems. The air sparging process involves the injection of air at some depth below the water table; as the air rises, VOCs transfer to the vapor phase and discharge to the unsaturated zone. In almost all applications, SVE is used to capture the sparging gas as well as to clean up the unsaturated zone. Several researchers have investigated air flow patterns, but relatively little ongoing research is being done to define the mass transfer rates that govern the performance of air sparging. This paper presents a model to quantify the removal mechanisms during air sparging. The model simulation is compared to an analytical solution and the dimensionless groups are analyzed to determine the dominant mass transfer processes. The model shows that mass transfer is dominated by gaseous dispersion and advection, and liquid diffusion.

Quantification of the Mechanisms Controlling the Removal Rate of Volatile Contaminants by Air Sparging

Air sparging has been used as an in situ technique to remove VOCs from contaminated groundwater: air is injected into the groundwater from an injection well, and the VOC partitions into the air phase and rises to the unsaturated zone, where another technique, such as soil vapor extraction, is used to remove the gases from the vadose zone. A computer model that accurately describes the process is needed. This project comprises model development and laboratory experiments, conducted independently. The model will be tested using the laboratory data. Only preliminary results are available. Preliminary laboratory column tests have been conducted along with some modeling to simulate the removal of a single VOC from a soil column. Comparison show that a finite element code is able to predict removal of methane and TCE. To determine if the air flow pattern in air sparging is predictable, experiments were done in a large-scale reactor and compared to numerical simulations.

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Gretchen L. Hein

Papers

Three‐Dimensional Experimental Testing of a Two‐Phase Flow‐Modeling Approach for Air Sparging

Quantification of the Mechanisms Controlling the Removal Rate of Volatile Contaminants by Air Sparging

Field-scale model for air sparging performance assessment and design