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Xm. Nevertheless, the ERT provided consistent apparent resistivity <br />pseudo sections with very few data outliers, which is a sign of good <br />data quality. After removal of a few noisy data points for two of the <br />lines (Table 1), true subsurface resistivity distributions were esti- <br />mated using the robust inversion (L1 norm) option which is better <br />at handling large contrasts in the resistivities than the least- <br />squares (L2 norm) optimisation method (Loke et al., 2003). The <br />resistivity inversion procedure was achieved using the inversion <br />software RES2DINV (Loke, 1999), which calculates the most likely <br />distribution of resistivity (Çınar et al., 2015). <br />Table 1 <br />Settings of the different ERT profile lines. <br />Parameter AL1 AL2 AL3 ML1 ML2 <br />Length (m) 80 80 40 80 55 <br />Electrode separation (m) 1 1 1 1 1 <br />Mean contact resistance (ohm) 2990 4010 2600 85,500 98,300 <br />Coeff. of variance of contact resistance (%) 63.1 62.7 61.8 96.4 98.8 <br />Pulse duration (s) 2.6 2.6 2.6 2.6 2.6 <br />Average current (mA) 102 67 104 11 5 <br />Average variance (%) 0.13 0.18 0.14 0.59 0.81 <br />No. of stacking in data acquisition 6 6 6 6 6 <br />No. of data acquired 1603 1603 833 1547 829 <br />No. of data inverted 1603 1603 833 1532 818 <br />No. of iterations 14 13 17 3 4 <br />No. of layers 15 15 10 15 13 <br />No. of blocks 1215 1215 410 1215 767 <br />Vertical to horizontal flatness ratio 0.5 0.5 0.5 1 1 <br />Width of the model cells (m) 0.5 0.5 0.5 0.5 0.5 <br />Resistivity mean residual (%) 3.0 5.0 3.5 10.5 11.1 <br />Fig. 2.(a) Sketch of separated electrode cable spreads used for the survey, and cables and electrodes setup along profile lines at (b) Alsterfors and (c) Madesjö. <br />216 R.N. Mutafela et al./Waste Management 106 (2020) 213–225