Enhanced thermal conduction remediates petroleum hydrocarbon pollution
Soil remediation at a former industrial site undertaken by Campbell Reith Hill (CRH), consulting environmental engineer, and MEL Ltd, remediation contractor, have utilised a new technique, not previously used in the UK, called Enhanced Thermal Conduction (ETC).
Approximately 1,500m³ of soils were found to be contaminated. Due to the sensitivity of the underlying Gravels aquifer and the adjacent surface water body, such levels were deemed unacceptable to be retained on site and following a more detailed assessment of the risks posed, a remediation criteria of 500 mg/kg TPH was agreed with the Environment Agency.
A range of remedial options was reviewed for the site including the use of biological techniques and "dig and dump". This review included consideration of existing time and financial constraints imposed by the client, and the use of ETC emerged as the most suitable option.
Remediation contractor MEL Ltd was able to demonstrate the effectiveness and suitability of this technique, based upon the extensive data available from its application in North America. ETC was able to offer guaranteed treatment times and achievement of the set remedial criteria. In addition it proved approximately 50% cheaper than the "dig and dump" option and was comparable in cost terms with the biological treatment techniques.
ETC remediates the soil by heating it to temperatures of between 250°c and 450°c (dependant upon the nature of the contaminant) to volatise the contaminants. As they volatise, the contaminants migrate to the space between the soil and the steel cover, where they are then drawn into a thermal oxidiser and destroyed. Application of the technology involves the excavation of the contaminated soils and placement in a three layered soil cell. Each layer contains 100mm steel pipes which are attached to 300mm manifolds running 25 metre in length. Burners are attached to the end of the 300mm manifolds on each level and provide the heated air. A stainless steel hut is constructed over the entire soil cell to prevent the escape of air during the soil treatment process.
The contaminated soils have been successfully treated by the ETC process, with validation sampling demonstrating residual TPH levels to be present in the range of non-detect to less than 50 mg/kg.
Treatment of each cell (comprising 500 metres of soil) has taken two weeks,
including one week for actual thermal treatment. CRH reports that the use of
ETC has satisfactorily achieved the end remedial targets and has met the project's
timescale and financial constraints.