Remediation in Northern Climates: How Can Petroleum Hydrocarbon Remediation be Assessed in Soils Under Seasonal Freeze-thaw Conditions?

Accurate assessment for bioremediation feasibility plays a critical role in developing cost-effective and efficient remediation strategies adapted to northern climates, where warm seasons are short and accessibility is limited. Using a pilot-scale bioremediation system, this study quantitatively assessed bioremediation feasibility under dynamic site temperatures, including summers and non-summers, at a northern contaminated site. A total of 15 first-order rate constants were derived from previous pilot-scale experiments carried out under dynamic or fixed average temperatures of a cold site. The biodegradation rate obtained from pilot-scale testing was two times slower than that of the microcosm-scale experiments, which have been widely used for laboratory-based assessments. Site temperature variability and seasonality at cold sites greatly influences biodegradation kinetics. Using pilot-scale experiments under site-representative freeze-thaw temperatures, the unfrozen water content, which is a requirement for microbial activity in freezing soils, was predicted based on a TEMP/W model. The simulated unfrozen water content was in excellent agreement with the measured unfrozen water content during soil freeze- thaw. The correlation between unfrozen water content and microbial C0₂ production was statistically 
significant. This study suggests that on-site bioremediation for cold site soils is feasible in summers and
can be extended to seasonal freeze-thaw months.