Monitoring nitrate natural attenuation and analysis of indigenous micro-organism community in groundwater

In the result of monitoring nitrate in about 6,000 groundwater wells around agricultural area, an average detection is about 9.0 mg/L and the excess rate of quality standard for drinking water was serious level as 45%. A shallow aquifer in some agricultural sites was highly contaminated showing 105–311 NO₃-mg/L. In this work, we evaluated monitorednatural attenuation (MNA) of nitrate by biological denitrification in highly nitrate-contaminated aquifer, known as effective technology to clean-up high concentration of nitrate, for confirming whether the groundwater is naturally remediated. We monitored nitrate degradation rate, microbial reaction (sulfate reduction, etc.) for 16 months according to oxidant and reduction rate. We also monitored microbial community change and amount of functional genes (noeZ and nirK) that encode for enzyme involved in denitrification pathway. In the result, since the groundwater was quiet oxidant condition, nitrate reduction was not monitored. However, there are functional genes and various microbial families related to denitrification process were detected such as methylomonas and methylomirabilis. These results indicate that there are possibilities of natural denitrification if the redox condition and other factors (carbon source, etc.) are supported. We also calculated the Hazard Index using RBCA Tool Kits to obtain remediation need of nitrate-contaminated groundwater.