Enhanced Natural Remediation of Nitrate by Pumping Groundwater from Active Denitrification Depth

The objective of this study was to propose a simple, low-cost in-situ remediation method for NO3−-N that effectively utilizes natural denitrification processes. We verified the inflow of surrounding groundwater containing high concentrations of NO3−-N when groundwater at the denitrification depth was pumped, as well as the denitrification effect at that depth, under two pumping flow-rate conditions (low and high) at a site where denitrification had been confirmed. The results suggest that pumping groundwater at the denitrification depth enables the inflow of surrounding groundwater, thereby enabling denitrification of high-concentration NO3−-N in the surrounding groundwater under oxidizing conditions. The denitrification amounts were 72 mg-N/h for the high-flow Pumped Denitrification Test (PDT) and 3.3 mg-N/h for the low-flow PDT. Additionally, the nitrate removal efficiency of the high-flow PDT was higher than the results obtained in previous studies at the same site and season under natural groundwater flow. It was also comparable to that of artificially created denitrification environments at other sites when assuming conditions with high NO3−-N concentrations in shallow groundwater. This study demonstrated that the pumping of reductive groundwater transports high concentrations of NO3−-N along with the surrounding groundwater, and that denitrification occurs without impairing denitrification capacity.