Enhanced Hydrocarbon Biodegradation via Soil Vapor Extraction System Operation

Soil vapor extraction (SVE) systems are a common remedial technology at hydrocarbon spill sites. The typical metric used to quantify the effectiveness of these systems is the mass of hydrocarbons removed through vapor extraction. However, SVE systems also draw atmospheric air (and associated oxygen) into the subsurface, potentially enhancing aerobic biodegradation. This study evaluates long‐term monitoring data from the extracted vapor of six SVE systems to quantify hydrocarbon removal via direct hydrocarbon extraction, aerobic biodegradation, and anaerobic biodegradation. Aerobic biodegradation rates were calculated from the magnitude of oxygen depletion and carbon dioxide enrichment in the extracted vapor. In contrast, anaerobic rates were estimated from methane enrichment when data were available. Results reveal that aerobic biodegradation may account for 39%–86% of the total mass removed, often exceeding the magnitude of direct hydrocarbon removal. Methanogenesis (a natural process likely not enhanced by SVE operations) contributed 5%–31% of total biodegradation at some sites with operating SVE systems, highlighting the significance of natural attenuation in these systems. Across the six sites, the findings underscore the importance of quantifying biodegradation as part of total hydrocarbon removal at sites with active SVE systems, providing insights for refining site management strategies.