Intermediate-scale Evaluation of Bioremediation Technologies in Heterogeneous Lnapl-contaminated Soil

Bioremediation is a potentially cost-effective, in situ method for cleaning up NAPL-contaminated sites. The ability of microorganisms to access and degrade NAPL constituents is highly dependent on the heterogeneity of the soil and the morphology of the NAPL source. Soil heterogeneities can result in preferential pathways of air and water flow through the subsurface. Intermediate-scale studies were conducted to evaluate two bioremediation alternatives for a railyard contaminated with aged diesel. Bioventing and biosparging technologies are based on the ability to introduce oxygen to the contaminated zone. Intermediate scale tests were conducted with aged diesel oil and soil obtained from the site to determine the ability of these technologies to deliver oxygen into a smear zone containing free-phase LNAPL. Results indicate the presence of soil heterogeneities and free-phase NAPL significantly reduce the efficiency of oxygen delivery. Both technologies can increase the overall dissolved-oxygen (DO) concentration in groundwater. However, the airflow occurs primarily through preferential pathways. The result is a lower oxygen delivery than expected , based on bulk-phase DO measurements.