Do conventional monitoring practices indicate in situ air sparging performance?

Short-term pilot tests play a key role in the selection and design of in situ air sparging systems. Most pilot tests are less than 24 h in duration and consist of monitoring changes in dissolved oxygen, water levels in wells, soil gas pressures, and soil gas contaminant concentrations while air is injected into the aquifer. These parameters are assumed to be indicators of air sparging feasibility and performance, and are also used in the design of full-scale systems. In this work the authors assess the validity of this critical assumption. Data are presented from a study site where a typical pilot-scale short-term test was conducted, followed by continued operation of a full-scale system for 110 days. Conventional sampling practices were augmented with more discrete and detailed assessment methods. In addition, a tracer gas was used to better understand air distributions, vapor flow paths, and vapor recovery efficiency. The data illustrate that conclusions regarding the performance and applicability of air sparging at the study site vary significantly depending on the monitoring approach used. There was no clear correlation between short-term pilot-test data and extended system performance when using data collected only from conventional groundwater monitoring wells. Attention is focused on petroleum hydrocarbons