Assessment of nitrate contamination in unsaturated zone of urban areas: The case study of Tehran, Iran

Modeling fate of nitrogen in unsaturated and saturated zone is a complex process, which requires detailed geochemical data. Complexities of the process as well as data insufficiencies are two major issues, which make quantitative assessment of the problem more complicated. In this work, a lumped-parameter model (LPM) is proposed that has been evaluated for a data-limited case to study temporal and steady-state behavior of Nitrate and Ammonium in unsaturated zone. The concentration of components in the model are assumed as the depth-averaged concentrations, and dispersive fluxes have been neglected. The case study area is Tehran City aquifer, which is highly contaminated by domestic wastewater discharge into the groundwater. Three sources for Nitrogen contamination have been studied, namely domestic wastewater, park/recreational applications, and wet deposition. Results show that Nitrate production in the first few meters (<5 m) is quite large. To compare the model results with the measurements, error estimation analysis based on Vornoi map has been fulfilled. Finally, it is shown that there is a fairly good correlation coefficient between simulation and measurements, which approves the validity of the LPM.