Performance expectations for in situ air sparging systems

In situ air sparging (IAS) is a remedial strategy commonly used to treat chemically contaminated soil and groundwater. IAS is considered a hybrid technology because the injected air is used to (a) physically strip volatile and semi-volatile contaminants, and (b) stimulate aerobic biotransformation of organic compounds. The demand for remediation technologies for soil and groundwater has outstripped the development of these technologies. Results from field implementation studies are a black box: they are known to work, but actual removal mechanisms are not clearly understood. Because of this, no widely accepted rational approach to utilizing these technologies has emerged, and the approach used to clean up a contaminated site relies upon the professional judgment of the individual designer.; This document introduces a design paradigm for application of IAS. The creation of this paradigm necessitated a better understanding of key processes affecting removal behavior, identification and development of new approaches for monitoring performance, and a clearly defined set of rules for designing and applying IAS systems. This research has been focused towards addressing these issues.; Physical model studies conducted to provide insight into the mechanisms and properties that control contaminant removal focused on NAPL and dissolved chemical treatment by IAS. Results showed that a diffusion model could explain dissolved chemical removal. They also suggest that performance decreases for chemicals with increasing Henry's Law coefficients, contrary to the popular belief that IAS treats high Henry's Law constant compounds effectively, but not low Henry's Law constant compounds. Pulsing was shown to increase cumulative dissolved chemical recovery by IAS.; Laboratory NAPL mixture source-zone experiments suggest that for the initial SVE-like chemical recovery stage, the primary factor driving removal is the chemical's partial vapor pressure, not its Henry's Law constant. Air injection rate was not found to alter the fraction of recoverable chemical, just the time in which that fraction was recovered. Further, these studies did not show significant improvements to recovery by pulsing the introduced air.; Field evidence demonstrated a different story. Dramatic improvements in cumulative chemical recovery by volatilization were observed as a result of increasing air injection rates and pulsing the air injection. Diagnostic tracer tests showed that on average, oxygen was delivered 0–30 mg-oxygen/L-water/day during system operation. These diagnostic tools also showed enhanced oxygen consumption for several months after shutdown, implying the intermittent air injection could be used to stimulate aerobic degradation of organic contaminants.; A field trial of the default design parameters from the new IAS Design Paradigm illustrates a system that effectively treats both BTEX compounds and MTBE. Overall, laboratory and field data show that treatment of MTBE by IAS is as good or better as it is for BTEX compounds.