- Hydrocarbon contaminated groundwater is increasingly remediated in-situ, using permeable reactive barriers (PRBs). However, there is a need for new non-invasive imaging techniques to assess the homogeneity and continuity of PRB emplacement and to test barrier performance with time. Recent BGS research shows that induced polarisation tomography (IPT) can be used to image PRBs and thereby monitor barrier performance non-destructively.
A variant of IPT known as spectral induced polarisation (SIP) has the potential to detect toxic non-aqueous phase liquids (NAPLs), including oils and solvents.
NAPLs pose a serious risk to groundwater and are resistant to biodegradation and natural attenuation.
Laboratory SIP experiments confirm that NAPL distributions and flow-paths can be detected in the complex frequency domain, using differential time-lapse imaging. Advanced 2.5D SIP inversion code has been developed which allows the earth’s multi-spectral response to be modelled in terms of Cole-Cole dispersion parameters. Residual NAPL saturation levels can be estimated from the resistivity models by applying Archie’s second equation. However, further work is needed to assess the practicality of SIP tomography at the field-scale.
Time-lapse monitoring of NAPL flow through porous media using SIP tomography has demonstrated that NAPL flow, distribution, and saturation levels can be monitored non-invasively using SIP imaging. Click on the image to download a movie file.
Contact the Geophysical tomography team