Use of an SF₆-Based Diagnostic Tool for Assessing Air Distributions and Oxygen Transfer Rates during IAS Operation

A Multi-Tracer Push-Pull Diagnostic Test for In Situ Air Sparging Systems

“…If true, this is a significant observation as practitioners currently infer IAS treatment zones based on groundwater DO measurements. While the spatial variations in acetate loss could be due to spatial variations in anaerobic biodegradation rates, the work of Amerson (1997) and Bruce et al (2001) supports the hypothesis that oxygenation occurred at points having sustained DO<1 mg/L. In their work, a gas tracer delivery diagnostic tool was used, and they report oxygenation rates similar to those from this work.…”

“…This range is also equivalent to zero-order biodegradation rates of 0 to 3 mg-hydrocarbon/kg-soil/d, and these are comparable to the lower end of the range of rates reported for bioventing in situ respirometry tests (Leeson and Hinchee, 1996). In addition, this range of rates is comparable to that reported by Bruce et al (2001) from use of a gas tracer diagnostic test at this site. The data suggest significant oxygen transfer at MP-1, MP-2, and MP-5 even though DO measurements remained ≤1 mg/L.…”

“…Alternatively, the discrepancy could be explained by differences in anaerobic degradation rates of acetate at the different points. However, the transfer of oxygen at points not showing elevated DO levels is reported by Amerson (1997) and Bruce et al (2001). In that work, a conservative tracer delivered in the gas injection stream was used to determine oxygenation rates at this site.…”

“…This tool is complementary to the inert tracer gas delivery diagnostic tool described by Bruce et al (2001), Johnson et al (1996), and Amerson (1997). The mechanics of this diagnostic test show some similarity to the push-pull tests described by Istok et al (1997) and Schroth et al (1998) for assessing microbial respiration during natural attenuation; however, the multi-tracer solution used and the data reduction approaches are different.…”

Diagnostic Tools for Integrated In Situ Air Sparging Pilot Tests

“…The objectives in injecting for a short, known period are: (1) to provide an opportunity for SF 6 transfer from the air to the groundwater without a significant amount of groundwater transport; and (2) to allow an estimate of the mass transfer coefficient at various locations to be determined. The details of these procedures are discussed by Bruce et al (2001). At the end of the SF 6 injection period, groundwater samples are collected and analyzed for SF 6 .…”