Dispersivity Values Determined from Effluent and Nonintrusive Resident Concentration Measurements

As indicated in the subsurface contaminant transport literature, the longitudinal dispersivity values needed to predict salt concentrations become smaller if more details of the flow field are included in the calculations. One way of determining these small‐scale or local longitudinal dispersivities is from breakthrough curves using laboratory columns. A gamma radiation technique is presented that allows non‐intrusive, in situ (resident) salt concentration measurements in saturated sand columns. The technique is demonstrated by means of a series of vertical displacement experiments with deionized water and a NaI solution in a column containing a medium sand. Longitudinal dispersivity values derived from the resident concentration breakthrough curves determined with this technique were consistently smaller than those derived from conventional effluent concentration breakthrough curves. The density configuration of the liquids may affect the apparent dispersivities.