Groundwater system responses to the 2016 ML 5.8 Gyeongju earthquake, South Korea

The September 12, 2016 Gyeongju earthquakes (ML = 5.1 of foreshock and ML = 5.8 of mainshock) had significant effects on groundwater systems along the Yangsan Fault System composed of NNE-trending, right-lateral strike-slip faults in Korea. Hydrological changes induced by the earthquakes are important because no surface ruptures have been reported and few earthquakes usually occur in Korea. The main objective of this research was to propose a conceptual model interpreting the possible mechanisms of groundwater response to the earthquakes based on anomalous hydrogeochemical data including isotope concentrations with lithostratigraphic classification. For this, annual monitoring data (groundwater level, temperature, and electrical conductivity) and collected data (hydrochemical parameters, radon-222, and strontium isotopes) were used. Groundwater level anomalies could be attributed to the movement of the epicentral strike-slip fault. Radon concentration data showed the potential of groundwater mixing processes. Strontium anomalies could be related to the lithology and stratigraphy of the bedrock, reflecting the effect of water–rock interaction. Using a Self-Organizing Map (SOM) statistical analysis, associations of hydro-geochemical characteristics among groundwater wells were interpreted. By combining the grouped results of the SOM with lithostratigraphic unit data, 21 groundwater wells were classified into four groups, each corresponding to different hydrogeological behaviors. A new comprehensive conceptual model was developed to explain possible mechanisms for the hydrological and geochemical responses in each group, which have been respectively identified as water–rock interaction, mixing of shallow and deep aquifers via sea water intrusion, bedrock fracture opening related to strike-slip fault movement, and no response

Aplicação de dados de multi-isótopicos e de datação de águas subterrâneas para identificar fatores que afetam a extensão da desnitrificação em um aquífero raso nas proximidades de um rio na Coréia do Sul

The extent of denitrification in a small agricultural area near a river in Yangpyeong, South Korea, was determined using multiple isotopes, groundwater age, and physicochemical data for groundwater. The shallow groundwater at one monitoring site had high concentrations of NO3-N (74–83 mg L−1). The δ15N-NO3 values for groundwater in the study area ranged between +9.1 and +24.6‰ in June 2014 and +12.2 to +21.6‰ in October 2014. High δ15N-NO3 values (+10.7 to +12.5‰) in both sampling periods indicated that the high concentrations of nitrate in the groundwater originated from application of organic fertilizers and manure. In the northern part of the study area, some groundwater samples showed elevated δ15N-NO3 and δ18O-NO3 values, which suggest that nitrate was removed from the groundwater via denitrification, with N isotope enrichment factors ranging between −4.8 and −7.9‰ and O isotope enrichment factors varying between −3.8 and −4.9‰. Similar δD and δ18O values of the surface water and groundwater in the south appear to indicate that groundwater in that area was affected by surface-water infiltration. The mean residence times (MRTs) of groundwater showed younger ages in the south (10–20 years) than in the north (20–30 years). Hence, it was concluded that denitrification processes under anaerobic conditions with longer groundwater MRT in the northern part of the study area removed considerable amounts of nitrate. This study demonstrates that multi-isotope data combined with physicochemical data and age-dating information can be effectively applied to characterize nitrate contaminant sources and attenuation processes

Application of natural and artificial tracers to constrain CO2 leakage and degassing in the K-COSEM site, South Korea

Although Carbon Capture and Storage (CCS)has been demonstrated successfully on many occasions, the potential leakage of deep sequestrated CO 2 into shallow groundwater remains a concern. To address this, an artificial injection experiment was performed at the K-COSEM test site in Eumseong, South Korea, that involved the release of CO 2 –infused water (16.9 kg of CO 2 in 5 m 3 )containing He and Kr tracers into a shallow, heterogeneous, weathered-granite aquifer. The initial CO 2 –fluid was slightly oversaturated at the subsurface injection point, and thus the plume was expected to initially degas CO 2 before equilibrating at in-situ conditions. Monitoring of carbonate system parameters in nearby observation wells helped define the evolution of the injected fluids, while the noble gas tracers were used to clearly define the physical behavior of the CO 2 plume (including an estimate of degassed CO 2 equal to 0.9–3.1%). This study demonstrates the potential use of noble gases for monitoring CO 2 leakage in shallow aquifers, constraining mass balance and phase changes of leaking fluids, and better understanding local flow pathways. Furthermore, breakthrough of noble gases in this study was different from some previous experiments, suggesting that monitoring efficiency of these tracers may depend on leakage and site conditions

Spatial trends of nitrate pollution and groundwater chemistry in Shimabara, Nagasaki, Japan

Groundwater contamination by nitrate is a common problem in many parts of the world. The agriculturally important Shimabara district in Nagasaki, Japan, is experiencing this problem. The general source of drinking water of the study area is groundwater and consequently the nitrate contamination is a significant problem. For this reason, a groundwater investigation was performed and water samples were collected at 40 locations including residential areas, public water supply wells, springs, and rivers from August 2011 to November 2013. Results showed that nitrate nitrogen (NO3-N) concentration is exceeding the Japanese drinking water quality standards (10 mg L?1) at 15 locations. Maximum NO3-N concentration was 26.6 mg L?1. Nitrate (NO?3) was strongly correlated with Cl? (r = 0.96), K+ (r = 0.68), SO2?4 (r = 0.66), and Ca2+ (r = 0.59), respectively. The high correlations with Cl? and K+ are related to livestock waste. Corresponding correlation with SO2?4 is related to chemical fertilizers and Ca2+ to calcareous material to neutralize acidic soil. Both the first and second components in principal component analysis reflect ion dissolution from aquifer matrix during groundwater flow along the mountain side towards the lower reaches of the alluvial fan. Using hierarchical cluster analysis, chemical characteristics of groundwater were classified into four clusters. One cluster is strongly related to the nitrate contaminated groundwater and the other clusters reflect the origin of the major ions in the groundwater