Chapter 7 Electrical resistivity methods 7.1 Introduction 418 7.2 Basic principles 418 7.2.1 True resistivity 418 7.2.2 Current flow in a homogeneous earth 424 7.3 Electrode configurations and geometric factors 426 7.3.1 General case 426 7.3.2 Electrode 427 7.3.3 Media with contrasting resistivities 433 7.4 Modes of development 441 7.4.1 Vertical electrical sounding (VES) 441 7.4.2 Automated array scanning 444 7.4.3 Constant-separation traversing (CST) 446 7.4.4 Field problems 447 7.5 Interpretation methods 453 7.5.1 Qualitative approach 453 7.5.2 Master curves 455 7.5.3 Curve matching by computer 457 7.5.4 Equivalence and suppression 461 7.5.5 Inversion, deconvolution and numerical modelling 464 7.6 Mise-a-la-masse method 467 7.7 Applications and case histories 470 7.7.1 Engineering site investigations 470 7.7.2 Groundwater and landfill surveys 475 7.7.3 Glaciological applications 482 7.8 Electrokinetic (EK) surveying in groundwater surveys 485 7.9 Leak detection through artificial membranes 488