Creation of an artificial frozen barrier using hybrid thermosyphons

Standard containment technologies for remediation of subsurface contaminants include slurry walls, reactive barriers, sheet piling, and grouting. Another less common technique is freezing contaminants in situ. Artificial freezing techniques can be used to create a frozen barrier that restricts migration of aqueous phase contaminants and, therefore, can provide subsurface containment at a variety of facilities, including underground tanks, nuclear waste sites, groundwater plumes, and in situ waste treatment areas. Frozen barriers are formed by using a series of subsurface freezing pipes. The adjacent soil forms a frozen column the length of the freezing pipe; and the diameter of the frozen soil column increases with time at a rate depending upon the specific soil properties, moisture content, and thermal conditions at a given site and refrigeration rate (i.e., pipe temperature). The barrier is completed once the increasing diameters of the frozen soil columns merge together, which is referred to as “freezing to closure”. A study was performed in Fairbanks, Alaska, to investigate how quickly a barrier can be created during the summer using actively cooled hybrid thermosyphons. Freezing to closure occurred after 42 days, the barrier was 1 m thick after approximately 49 days, and temperatures were below − 3 °C at the core of the barrier (in between the thermosyphons) after 60 days. The active system was turned off in the fall, and passive cooling of the ground continued through the winter. By the beginning of the following March, the frozen barrier was 3.8 m thick.