Thermally enhanced bioventing of petroleum hydrocarbons in cold regions

Abstract

Petroleum-based contamination of the environment has and will likely continue to be a problem as long as oil and natural gas supply much of the world energy demands. In cold regions, where vast quantities of these fuels are extracted and used, climate and frozen soils limit remedial efforts to a few technologies. Bioventing has shown promise as a viable method for the remediation of spilled petroleum-based fuels in cold regions. An in situ study of bioventing with soil warming was conducted at a Fairbanks, Alaska site. The main purpose of this research effort was to compare the effectiveness of thermal enhancement techniques applied to bioventing. Objectives included (1) developing a suitable thermal insulation system(s) that would provide year-round bioventing of petroleum contaminated soils, (2) modeling of the thermal regime below three treatment areas, (3) relating monitoring and testing data to thermally enhanced biodegradation, and (4) presenting the information in a way that is useful to engineers, biologists and environmental scientists. Active soil warming with electrical heat tape beneath polystyrene insulation and sand and gravel overburden raised subsurface soil temperatures from the ground surface to the water table by as much as 15$\sp\circ$F. The actively warmed test plot was successfully heated year-round, preventing soil freezing and enhancing microbial activity. Soil gas, microbiological, and geochemical sampling data evidenced correlation between increased bioactivity and soil warming. Passively treated soils evidenced some winter increase in temperatures, although some periodic soil freezing did occur. Overall, biodegradation within both passively treated and untreated contaminated test plots was noticeably slower than within the actively warmed plot. Thermally enhanced bioventing successfully remediated hydrocarbon contamination in vadose zone soils at a subarctic site within two years. After oxygen, temperature appears to be the most important factor affecting microbial activity and biodegradation. Variable and low moisture contents did not seem detrimental to bioactivity.