In Situ Electro-Thermal Extraction Dynamic Stripping Beneath an Inhabited Apartment Building

This paper presents the implementation and results of ET-DSP^TM, an in-situ electrical soil heating technology, in combination with high vacuum dual phase extraction, to achieve the removal of vapour pressure sensitive BTEX compounds from under an occupied residential apartment building. Operating within several engineering, environmental, and safety constraints, a design was developed in order to conduct electrical heating and in-situ extraction operations unobtrusively to the day to day living of the residents within the apartment complex and general area.

To place electrodes and extraction wells beneath the building into the contaminated volume of soil required that an entire apartment suite be converted into an operational site where drilling operations could be conducted in conjunction with the placement of surface facilities. The extraction facilities and ET-DSP^TM system were designed in such a manner that noise levels were reduced to well below acceptable levels and induced surface voltages were virtually eliminated. The standard operating procedures were also produced so that onsite activities of field personnel were kept to a minimum. One of the objectives of this paper is to present in detail the implementation strategy and economic factors.

This is the third implementation of ET-DSP^TM by Shell Canada Products Ltd in Canada. In a typical application of the process, electrodes are strategically placed into the contaminated zone. The pattern of electrodes is designed so that conventional three-phase power can be used to heat the soil. Also, the distance between electrodes and their location is determined from the heat transfer mechanisms associated with vapour extraction, electrical heating and fluid movement in the contaminated zone. Without consideration of all the heat transfer mechanisms, a less effective heating process will result. To determine the ideal pattern of electrode and extraction wells, a multi-phase, multi-component, three-dimensional thermal model is used to simulate the process. Operational data were monitored and compared to the numerical simulation of the process. Excellent agreement between field temperature, electrical operating, and energy consumption data and the numerical simulation predictions was observed. An additional objective of this paper is to present the results of the numerical simulation for this project in light of the field measured performance data.

During the remediation process several confirmatory samples were extracted from the target soil. The results consistently showed a significant reduction in the concentration of the hydrocarbons with non-detect levels being achieved in the majority of the samples. This is a direct result of a substantial temperature increase of the soil and concurrent increase in the hydrocarbon vapour pressure. The operations of the high vacuum dual phase extraction system were optimized to recover the hydrocarbon vapours and dissolved phase concentrations from the soil as they were created. A final objective of this paper is to present the remediation performance achieved at this site with confirmatory drilling data and vapour concentration levels over time.