Comparing Groundwater Sampling Devices for Denitrification Assessment Using the N 2 /Ar Method

Ground Water, vol. 64, pp. 235–242

Abstract

Abstract The N 2 /Ar method is valuable for studying legacy nitrate and denitrification progress in groundwater systems. It uses dissolved N 2 and Ar concentrations to calculate the amount of N 2 originating from denitrification (excess‐N 2 ). Successfully applying the method requires accurate values of N 2 and Ar concentrations. Therefore, avoiding degassing and atmospheric contamination during groundwater sampling is crucial for reliable results. In this study, we focus on the effect of sampling devices on N 2 , Ar, and the resulting excess‐N 2 concentrations. To evaluate this effect over a wide concentration range, we sampled 14 observation wells. One sample was collected using a submersible pump and another using a bladder pump. Furthermore, we collected multiple samples with both pumps at a fifteenth site to assess reproducibility. Additionally, we used a point‐source bailer for sampling at this site. The major ion concentrations show that the sampling device does not significantly influence the sample chemistry. In contrast, the measured N 2 , Ar, and calculated excess‐N 2 concentrations significantly differ between the sampling devices. Overall, the samples collected with the submersible pump show the highest N 2 and Ar concentrations, resulting in the highest excess‐N 2 concentrations. N 2 and Ar concentrations of the bladder pump samples are lower, resulting in lower excess‐N 2 concentrations. The bailer samples show lower N 2 but similar Ar concentrations to the submersible pump samples, leading to the lowest excess‐N 2 concentrations. We conclude that a submersible pump is practical and suitable for collecting groundwater samples to assess denitrification by the N 2 /Ar method.

Authors 2

1. Felix Fahrenbach corresponding Aachen Corresponding Author

   RWTH Aachen University

   Affiliation as printed

   Corresponding author: RWTH Aachen University, Institute of Hydrogeology, Lochnerstr. 4-20, 52064 Aachen, Germany; [email protected]

2. Thomas R. Rüde Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University Institute of Hydrogeology Lochnerstr. 4‐20 52064 Aachen Germany