• Economic and Environmental Geology
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• v.41 no.6
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• pp.645-655
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• 2008

The Cr(VI) concentrations at the shallow aquifer well (MPH-0-1) of the Moonpyung groundwater monitoring station were in the range of 0.5 to 3.1 mg/L exceeding 10 to 62 times the guideline for drinking-water quality, indicating continuous contamination. However, Cr was not detected at the deep bedrock well and the other subsidiary monitoring wells except for MPH-1 and 6. Cross-correlation analyses were conducted for rainfall and groundwater level time series, resulting in the mean time of recharge after precipitation events to be 5.6 days. For rainy season, the water level was raised and the Cr(VI) concentration was several times lower than that during dry season at well MPH-0-1 well. Correlation of the Cr(VI) concentration with the groundwater-level showed that the Cr(VI) reduction was closely related with the groundwater-level rise in the well. However, the groundwater level rise during high water season induced the lateral migration of the Cr(VI)-contaminated groundwater at well MPH-4. We enriched and isolated a chromium reducing bacteria, Enterobacter aerogenes, from the Cr(VI)-contaminated groundwater in the wells MPH-0-1 and MPH-1. The bacteria may play an important role for immobilizing Cr(VI) in the Cr(VI)-contaminated groundwater. Therefore, the migration of the contaminant (Cr(VI) must has been restricted because of the natural attenuation by microbial reduction of Cr(VI) in the groundwater. This research suggests that the bioremediation of the Cr(VI)-contaminated groundwater by the indigenous bacteria may be feasible in the Cr(VI) contaminated groundwater.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.555-566
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• 2008

Hydrogeochemical study in Samseung area (Boeun, Chungbuk) and waterrock interaction experiment using rock samples from the area were performed to elucidate the fluoride source in groundwater and explaining geochemical behavior of fluoride ion. Fluoride concentration of public water supply mostly using groundwater in Boeun area was significantly higher in South Korea. The maximum fluoride concentration of the study area was 3.9 mg/L, and 23% of samples exceeded the Korean Drinking Water Standard of fluoride (1.5 mg/L). The average concentration of fluoride was 1.0 mg/L and median was 0.5 mg/L. Because of high skewness (1.3), median value is more appropriate to represent fluoride level of this area. The relationships between fluoride ion and geochemical parameters ($Na^+$, $HCO_3$, pH, etc.) indicated that the degree of waterrock interaction was not significant. However, high fluoride samples were observed in $NaHCO_3$ type on Piper's diagram. The negative relationship between fluoride and $NO_3$ ion which might originate from surface contaminants was obvious. These results indicate that fluoride ion in groundwater is geogenic origin. The source of fluoride was proved by waterrock interaction batch test. Fluoride concentration increased up to 1.2 mg/L after 96 hours of reaction between water and biotite granite. However, the relationship between well depth and fluoride ion, and groundwater age and fluoride ion was not clear. This indicates that fluoride ion is not correlated with degree of waterrock interaction in this area but local heterogeneity of fluoriderich minerals in granite terrain. High fluoride concentration in Boeun area seems to be correlated with distribution of permeable structures in hard rocks such as lineaments and faults of this area. This entails that the deep bedrock groundwater discharges through the permeable structures and mixed with shallow groundwater.