Assessment of Electrical Conductivity As a Surrogate Measurement for Water Samples in a Tracer Injection Experiment.

The transport behavior of solutes in streams depends on chemical, physical, biological, and hydrodynamic processes. Although it is a very complex system, it is known that this behavior is greatly influenced by surface and subsurface flows. For this reason, tracer injection in the water flows is one of the most extensively used approaches to evaluate the solute transport processes.  A properly design experiment and sampling strategy can yield solute concentration data spatially and temporally to evaluate transport and storage models. Electrical conductivity (EC) measurements have been used to quantify the tracer breakthrough.  Since EC data can be obtained automatically at high frequency, we are interested in knowing whether EC readings can be used as surrogates for analyzed chemical concentrations from collected water samples, because water sample collection and the subsequent analytic work are time consuming and laborious. An injection study was conducted in a 20-m flume, filled with sediments from a drainage ditch, under seepage, saturation and drainage conditions. Bromide and phosphate solutions were injected and monitored along the flume.  EC was automatically recorded at five different locations along the flume. Water samples were collected every minute and analyzed for bromide and phosphorus in terms of total mass.  In this presentation, we will discuss the potential advantages and issues with using easily obtained EC data as a surrogate for phosphorus and bromide transport in surface flow. In sum, for both phosphorus and bromide concentrations, EC data constituted a reasonable surrogate measurement for water samples in tracer injection experiments with particularities that will be discussed along this work.