These files contain Electric Resistivity Ground Imaging (ERGI) data measured using a Tigre 128 electric resistivity system with 64 electrodes in a roll-along survey mode. The electrodes were spaced 5 m apart and used in a Wenner a array configuration. The format of the file names is as follows: The two digits following B (18 or 20) is a label indicating the measurement site The digit following the T (1, 2 or 3) is the measurement transect number The next six digits, following the underscore, are the measurement date (ddmmyy) The next two digits, following the second underscore, are the survey number (measurements were repeated multiple times) The files are in tab delimited ascii text format, with three columns of data: Column 1 contains the distance measured across the survey transect Column 2 contains the a-spacing (the distance between adjacent electrode pairs) in m Column 3 contains the measured apparent resistivity value in Ohm m