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In Situ Smouldering Combustion (STAR): Meeting Remedial Goals in Complex Environments
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STAR is an innovative remediation technology based on smouldering combustion where the contaminants are the fuel. Like all in situ techniques, STAR faces many challenges for successful implementation.

This presentation highlights the interplay between key controlling variables and design to achieve optimal application of STAR in complex, real-world environments.

Field applications of STAR (full scale and pilot) will be presented, highlighting the challenges associated with implementing the technology in complex environments, as well as the techniques and strategies developed to mitigate these challenges. Additional data collected from rigorous laboratory studies elucidating key features of smouldering combustion critical to the successful implementation of STAR in the field will also be presented. Challenges such as "clean" gaps and interbedded clay layers, and mitigation strategies such as "seek and destroy" and surrogate fuels will be discussed.

STAR is best suited to the treatment of low volatility compounds (e.g., coal tar, creosote, heavy hydrocarbons) in silts or coarser materials. STAR is rapid, scalable, sustainable, and safe, and can be implemented surgically to focus remediation efforts to specific target treatment zones.

However, as the contaminant is the fuel source for remediation, STAR requires a minimum total petroleum hydrocarbon (TPH) concentration (typically on the order of 3,000-5,000 mg/kg TPH) to remain self-sustaining (i.e., for the reaction to propagate without energy input following ignition). Concentrations below this level will be combusted and the process can tolerate "gaps" in contaminant distribution on the order of feet, as a rigorous combustion study will illustrate.

High volatility compounds can be challenging for STAR, as these compounds (e.g., gasoline) are typically volatilized faster than they can be combusted during the ignition process. However, a surrogate fuel such as vegetable oil can be added to the target treatment zone to act as the primary fuel for combustion, which in turn volatilizes the contaminants for subsequent capture and treatment at ground surface. The effectiveness of this method will be illustrated by comparing "standard" STAR versus "vegetable oil-enhanced" STAR in a pilot test at a former refinery site.

Soil type is also an important consideration for STAR. STAR can not be applied in clay units; however, STAR is tolerant of clay layers and lenses within a generally coarser target treatment zone. Two case studies will illustrate how the smouldering process is able to overcome the presence of soil heterogeneity.

The advantages, limitations (and their mitigation strategies) of STAR will then be summarized through the presentation of a full-scale application of STAR at a former industrial facility. Operations involving ~2,000 ignition points as well as remedy verification activities were successfully completed in September 2019, demonstrating how STAR can meet remedial goals in complex environments.

Publication Summary

  • Geosyntec Authors: Gavin Grant
  • All Authors: Gavin Grant
  • Title: RPIC 2021
  • Event or Publication: Event
  • Practice Areas: Contaminated Site Assessment and Cleanup
  • Citation: Contaminated Site Assessment and Cleanup Citation: Geosyntec, Savron (a Geosyntec company), and SiREM (a Geosyntec company practitioners will present virtually at the Workshop from November 15-18, 2021.
  • Date: November 15-18, 2021
  • Location: Online
  • Publication Type: Platform Presentation