FIG. 2. Profiles of NO₃ extracted from vadose zone sediment cuttings and NO₃ concentrations in groundwater (after McMahon et al., 2006). Note the break in the x-axis scale at the UMA and GNT sites. Horizontal dashed lines in each plot represent water table depths at indicated times. In groundwater, concentrations plotted on a mass basis were calculated from concentrations measured on a volume basis (in parentheses) and porosity and bulk density data from McMahon et al. (2003). Zones of high NO₃ are commonly associated with indicated zones of N₂O production.