Groundwater vulnerability assessment by determining maximum contaminant loading limit in the vicinity of pumping wells

摘要

A method to determine maximum contaminant loading limit in the vicinity of pumping wells is introduced. The method is based on numerical modeling of solute transport applying the adjoint-derived backward equation of the general advection-dispersion equation (backward transport equation). A general idea of the backward transport equation is illustrated and also the compatibility of the equation with the advection-dispersion equation is shown through a numerical test. Then a process to derive contaminant concentration at pumping wells is presented, based on which one can determine the maximum contaminant loading limit to satisfy given criteria of the water quality at pumping wells. This method is applied to a field site in Buk-myeon and Daesan-myeon located in Changwon city, South Korea. The maximum loading limit of nitrate from the potential source loading area near pumping wells in concern is estimated to be 1.95 × 10 kg-N/m in consideration of denitrification, and 9.55 × 10 kg-N/m with no regard of it to satisfy the Drinking Water Quality Standard of nitrate in Korea. Since the annual average application rate of total nitrogen fertilizers in Korea is estimated to be 3.54 × 10 kg-N/m , understanding the geochemical condition of the area would be needed to suggest whether to reduce the fertilizer loading rate or not.