Fig. 1

a Fe K-edge XANES spectra of groundwater colloids (blue lines) and soil samples taken from a three-meter soil core (red lines). The zoomed insert shows the position of the pre-edge features: of the two sample types, the pre-edge features of the soil samples are shifted to a lower energy. The three-meter soil core was taken \(\sim\)14.2 m from the injection point of the remedial solution, adjacent to one of the monitoring wells from which colloids were sampled. b The pre-edge features of Fe K-edge XANES spectra (black dots) of a soil sample (top) and a groundwater colloid (bottom). A linear + Lorentzian model (green line) was used to determine the background-corrected pre-edge intensities. The background-corrected pre-edges were either modeled with two Gaussian peaks [dashed blue lines in inserts] or modeled with one Gaussian peak. Red lines represent fitted pre-edge peaks. Centroids and integrated intensities estimated from fit models were used to estimate Fe(II) and Fe(III) percentages