Resistivity and induced polarization methods are used for a wide range of near-surface applications, including hydrogeology, civil engineering and archaeology, as well as emerging applications in the agricultural and plant sciences. This comprehensive reference text covers both theory and practice of resistivity and induced polarization methods, demonstrating how to measure, model and interpret data in both the laboratory and the field. Marking the 100 year anniversary of the seminal work of Conrad Schlumberger (1920), the book covers historical development of electrical geophysics, electrical properties of geological materials, instrumentation, acquisition and modelling, and includes case studies that capture applications to societally relevant problems. The book is also supported by a full suite of forward and inverse modelling tools, allowing the reader to apply the techniques to a wide range of applications using digital datasets provided online. This is a valuable reference for graduate students, researchers and practitioners interested in near-surface geophysics.

Abstract. Abstract: Better understanding of field-scale unsaturated zone transport mechanisms is required if the fate of contaminants released at the surface is to be predicted accurately. Interpretation of results from direct tracer sampling in terms of operative hydraulic processes is often limited by the poor spatial coverage and the invasive nature of such techniques. Cross-borehole electrical imaging during progress of saline tracer migration is proposed to assist investigation of field-scale solute transport in the unsaturated zone. Electrical imaging provides non-destructive, high density and spatially continuous sampling of saline tracer transport injected over an area of the ground surface between two boreholes. The value of electrical imaging was tested at a field site on an interfluve of the UK Chalk aquifer. Improved understanding of active transport mechanisms in the unsaturated zone of the UK Chalk is required to predict its vulnerability to surface pollutants. In a tracer experiment in May 1996, a conductive saline tracer was infiltrated over 18 m2 at an average rate of 47 mm day-1 for 56 hours. Cross-borehole images obtained during and after infiltration show a large, homogenous, resistivity reduction in the top 3 m, no change between 3 m and 6 m depth, and smaller, inhomogeneous, resistivity reductions below 6 m depth. The resistivity has reduced at down to 15 m depth less than 2 days after tracer infiltration began. Hydrological interpretation of a sequence of electrical images obtained prior to, during, and up to three months after tracer injection suggests: (1) rapid tracer entry into the soil zone and upper 2 m of weathered Chalk, (2) intergranular transport of the bulk of the tracer, (3) a significant fissure flow component transporting tracer to at least 15 m depth in 31 hours, and (4) vertical changes in transport mechanisms possibly caused by interception of fissures by marl layers. The results of this experiment suggest that electrical imaging can assist the description of unsaturated zone hydraulic mechanisms through visual identification of spatial and temporal variations in transport processes.

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There is an increasing need to characterize fractured rock systems and to monitor the movement of fluids in these systems. Fractured rock aquifers are increasingly exploited for water resources, and are subject to contamination from industrial activities at the Earth's surface. Deep rock repositories of hazardous waste must be carefully characterized in terms of fracture transport characteristics. More recently, there has been a surge in technologies designed to increase permeability of shale reservoirs by creating fractures to promote fluid removal. However, fractured rock systems present unique challenges for characterization and monitoring technologies. Fracturing typically generates highly heterogeneous and anisotropic systems, making the evaluation of the distribution of physical properties from sparse subsurface measurements particularly problematic. Geophysical imaging technologies are increasingly applied in an effort to overcome the limitations of sparsely located direct observations of subsurface properties. However, the application of geophysical technologies to fractured rock systems presents challenges for imaging as appropriate regularization model constraints for complex, heterogeneous systems are hard to define without additional subsurface information.

ABSTRACT. Bor eh ole-based elec tri cal res isti vity sur veys have th e cap acity to enha n ce our understa nding of the structure of englaeial dra in age pathways in temperate ice. We summarize inter-borehole electrical resisti vity to m og raphy (ERT ) as currently used in hydrogeological inves tigation s and as ada pted fo r im aging eng lac ia l drainage. ERT co nn ections were successfull y m ad e fo r the first time in glacier ice, foll owing artificia l mineralization of borehole waters a t H aut Glacier d 'A roll a, Switzerl a nd. H ere, two typ es of electrical conn ection were m a de between boreh o les spaced up to 10 m a part and drill ed to depths of b etween 20 and 60 m. M ost tests indicated the presence o f resistively homogeneous ice with uniform bulk resistivities of ~ IO B -10 9 n m. However, ERT was also successfull y used to identify and characte ri ze a hydraulica ll y conducti ve eng lacial fr act ure tha t intersected two boreholes at a depth of ~ 13 m below th e glacier surface. The presence of thi s co nnecting void was suggested by drilling record s a nd ve rified by du a l boreholeimpulse testing. The reco nstructed tom ogra m for th ese b o reholes is cha rac terized by a backg round ice-resisti v ity field of ~ 10 9 n m that is disrupted at a depth of ~ 13 m by a sha rp, sub-hori zo ntal low-resistivity zone (~IO-l n m). Int er-borehole ERT, th erefore, has the cap acity to image b oth uniform a nd fractured temper a te glacier ice.

Borehole-based electrical resistivity surveys have the capacity to enhance our understanding of the structure of englacial drainage pathways in temperate ice. We summarize inter-borehole electrical resistivity tomography (ERT) as currently used in hydrogeological investigations and as adapted for imaging englacial drainage. ERT connections were successfully made for the first time in glacier ice, following artificial mineralization of borehole waters at Haut Glacier d’Arolla, Switzerland. Here, two types of electrical connection were made between boreholes spaced up to 10 m apart and drilled to depths of between 20 and 60 m. Most tests indicated the presence of resistively homogeneous ice with uniform bulk resistivities of ~108- 109Ω m. However, ERT was also successfully used to identify and characterize a hydraulically conductive englacial fracture that intersected two boreholes at a depth of ~ 13 m below the glacier surface. The presence of this connecting void was suggested by drilling records and verified by dual borehole-impulse testing. The reconstructed tomogram for these boreholes is characterized by a background ice-resistivity field of ~109Ω m that is disrupted at a depth of ~13 m by a sharp, sub-horizontal low-resistivity zone (~104Ω m). Inter-borehole ERT, therefore, has the capacity to image both uniform and fractured temperate glacier ice.