The trench was designed to provide in-situ flow-through treatment of VOCs by a combination of volatilization and aerobic biodegradation, and arsenic by precipitation and sorption. Various laboratory and field-scale tests were performed to evaluate the effectiveness of the trench in removing COCs. The results of laboratory, field-scale testing, and a stripping analysis indicated that the trench could remove the majority of VOCs that are present at the site by air sparging. Organic compounds that are not expected to be completely volatilized were projected to degrade by aerobic microorganisms in the oxygenated groundwater within and down-gradient of the trench.

 Geochemical modeling was performed to evaluate the ability of oxidizing conditions within trench to remove dissolved arsenic from groundwater through co-precipitation and sorption onto iron oxides. The modeling results indicated that oxidizing conditions created in the trench will result in precipitation of dissolved arsenic and other reduced minerals into the void spaces of the trench backfill material, significantly reducing the dissolved arsenic levels down-gradient of the trench.

 Long-term performance issues (i.e., mineral precipitation and biofouling) observed at other air sparging trenches were evaluated and solutions for such potential issues were incorporated in the design.  The air sparging trench alternative evaluation resulted in an amendment of the original ROD with a substantial cost saving to the client.