Background/Objectives: In-situ thermal remediation has been widely applied to treat highly contaminated source zones at current and former industrial and military sites. In many cases these thermal treatment systems are heating and extracting volatile compounds with low flash points, but these extracted compounds are safely contained within extraction piping and treatment systems. What happens when a thermal treatment system must be installed at an active chemical plant, refinery, or operating tank farm, and within an area that the owner has designated as a hazardous (classified) area? Under the National Electrical Code (NEC, NFPA 70) and OSHA regulations, a hazardous (classified) area is defined as an area where fire or explosion hazards may exist under normal or abnormal conditions, due to the presence of flammable, combustible or ignitable gases, vapors, or liquids, combustible dust, or ignitable fibers. Safely heating the subsurface to temperatures of 100°C or higher using electrically powered heaters, or gas burners, in a hazardous area poses special challenges and requires careful consideration during design and throughout subsurface heating operations.
Approach/Activities: The NEC classifies hazardous locations into several Classes, Divisions and Groups (or Zones and Groups) to define the type of hazard that exists, and under what conditions the hazard is expected to be present. Developing a safe design for use in a hazardous location is not as simple as selecting some appropriately rated parts from a catalog. Conformance to NEC and OSHA standards for installations in hazardous locations requires a thorough evaluation of the contaminant present in the subsurface, the source of the potentially hazardous atmosphere (which may be a completely different chemical), and the expected operating conditions during the thermal remediation program, to develop a safe design and operational plan.
Results/Lessons Learned: Two case studies will be presented to review different approaches for safely conducting an in-situ thermal remediation project within a designated hazardous location. Thermal Conduction Heating (TCH) was selected to remediate a historic chlorinated solvent release in close proximity to a loading rack handling a range of flammable fuels and other chemicals at an active tank farm facility. In another case, a combination of TCH and steam enhanced bioremediation were selected to remediate soil and groundwater contaminated with BTEX, naphthalene and chlorobenzenes, within a designated hazardous location footprint at an operating chemical plant. Both cases posed unique challenges for safely implementing the thermal remediation remedy. Potential solutions, design alternatives and considerations will be reviewed, and an innovative hazardous location rated TCH wellhead configuration developed for one of the sites will also be discussed. Operating results from deployment of this first of its kind hazardous location rated TCH wellhead will be shared. These cases demonstrate that with proper evaluation, design considerations and careful operation, in-situ thermal remediation can be safely accomplished even in potentially hazardous (classified) locations.