Geochemical Characteristics and Nitrates Contamination of Shallow Groundwater in the Ogcheon Area

The geochemical and nitrogen isotopic analyses for shallow groundwater of Ogcheon area were carried out to characterize the geochemical characteristics of the groundwater and to identify the source of nitrate. Groundwater shows a neutral pH to weakly alkalic condition with pH values ranging from 6.9 to 8.4. The average of EC, Eh and DO is 344.2 mu S/cm, 195 mV, 4 mg/L, respectively. According to piper diagram, chemical composition of groundwater is dominantly characterized by Ca-HCO3 type. On the other hand, groundwater type in the study area include CaCl+NO3 type that were highly influenced by agricultural activities. NO3-N concentration of the collected samples (n=45) range from 12.4 to 34.2 mg/l. These data show that the NO3-N concentration exceeds Korea Drinking Water Standard (10 mg/l). The delta N-15-NO3 values range from 2.7%o to 18.8 parts per thousand. The enrichments of heavy isotope in the groundwater indicate that major origin of nitrate pollution were associated with animal and human waste. Also the denitrification may have partly contributed as one of the sources of nitrogen.