The effectiveness of injected carbon sources in enhancing the denitrifying processes in groundwater with high nitrate concentrations

•Confirming that a biological degradation by indigenous microorganisms or chemical degradation by minerals occur.•Confirming that there is no natural decrease of nitric nitrogen by naturally existing indigenous microorganisms.•Promoting a growth and reaction of dechlorination related microorganisms at the site by injecting external carbon sources.•Providing basic factors required for the guideline in managing nitric nitrogen pollutant through active natural attenuation.