Advances in Remediation of Fractured Bedrock Using In Situ Thermal Treatment Technologies

Following an extensive programme of site characterisation using a variety of High Resolution Site Characterisation techniques, chlorinated solvent impact was identified beneath one area of the site discussed.  The majority of the contaminant mass was within the matrix of saturated bedrock; the most challenging environment to successfully perform in-situ remediation given the confined and fractured nature of the subsurface.

A risk reduction strategy of mass recovery to the extent technically, practically feasible and sustainable was agreed with the regulatory authorities and following an options appraisal, soil and groundwater remediation was undertaken using thermally enhanced Soil Vapour Extraction (SVE) to liberate contaminants from the bedrock.

Whilst several full scale steam injection projects have been undertaken in the UK, since the first application in 2005, SVE has traditionally been undertaken within either a naturally occurring unsaturated zone or one created via dewatering.  At this site the aquifer was found to be highly transmissive and confined by low permeability clay, making both of these options technically unsuitable.  Operation of the remediation system was therefore focussed upon 1) heating the clay from beneath to artificially increase its permeability and 2) development of a ‘steam bubble’ to allow vapour recovery through a zone created by boiling the groundwater.

The results demonstrate considerable success of the above approach with total mass removal calculated at circa 1,100kg after 12 weeks of system operation.

The application of this remediation approach in a complex fractured bedrock setting provides confidence that a similar approach could be taken on other sites where remediation has previously been viewed as technically unachievable.