Formatted Title
Application of Radiocarbon-Corrected Soil Gas Fluxes to Quantify the Field Degradation Rates of Chlorinated Solvents
Background/Objectives
Biodegradable contaminants break down into dead-end products in stoichiometric proportions. This concept has resulted into the now standard practice of directly measuring field LNAPL and petroleum contaminant degradation rates using respirometry techniques. This presentation will discuss how similar principles apply to the biodegradation of chlorinated solvents and present data from multiple case studies, so that stake holders (site managers, regulators, consultants) can incorporate these data into their site management decisions.
Approach/Activities
Chlorinated solvents that biodegrade produce stoichiometric amounts of ethane or ethene, which under aerobic conditions, rapidly break down into the dead-end byproduct carbon dioxide in the soil. E-Flux technique consists of capturing the carbon dioxide emanating from soil at grade (soil gas efflux) using a passive trap that is deployed for multiple days at the ground surface, providing the long-term average flux out of the soil. The carbon content of the trap is measured, and a correction based on radiocarbon (14C) analysis is applied to eliminate modern carbon interferences produced by soils due to processes not related to chlorinated contaminant biodegradation. The resulting time-weighted average fossil fuel CO2 flux relates directly to the field rate of chlorinated solvent biodegradation.
Results/Lessons Learned
E-Flux carbon dioxide fossil fuel traps have been now used multiple sites contaminated with chlorinated solvents. The data have been compared to other field measurements for validation, including in-well soil respirometry techniques and the biodegradation model Remchlor. The results indicate that chlorinated solvent biodegradation rates are measurable with this technique, offering a new alternative for direct, easy to implement technique to aid in the risk assessment and risk management of chlorinated solvent contaminated sites. This presentation will cover the principles of the measurement, a how-to-use overview, and the results of these measurements at multiple pilot sites.