The Canadian Society for Bioengineering

Abstract Nitrates when found in excess in the groundwater, is a health hazard. Nitrates can easily be transported by groundwater movement and may eventually reach aquifers located far away from the contamination location. It is important to monitor the nitrate movement in the groundwater to predict the extent of nitrate contamination. Traditionally, nitrate movement is monitored by sampling groundwater and analyzing it in the laboratory. This paper presents an in situ method to measure nitrate concentration in a laboratory flow experiment using time domain reflectometry data. Three flow cells (replicates) packed with a silty loam soil were subjected to a constant hydraulic gradient inducing saturated water flow through the flow cells. A 500 mg L NO3-N strength potassium nitrate solution source was connected at the inflow end and the nitrate concentration change with time was monitored along the length of the flow cells by soil solution sampling and analyzing it in the laboratory for NO3-N concentration. At the time of sampling, Time Domain Reflectometry (TDR) wave forms were recorded using the TDR mini-probes inserted at regular intervals along the length of the flow cells. The bulk soil electrical conductivity and the water content values extracted from the TDR wave forms were used to predict the nitrate concentrations at different locations. The nitrate concentration values predicted from the TDR data correlated well with the nitrate concentrations obtained through soil solution sampling method indicating the possibility of using TDR for monitoring nitrate movement in the groundwater non-destructively.