PartⅠ Characteristics of water level change from National Groundwater Monitoring Network, Korea

Analyses of long-term water level data (more than 5 years) of NGMN (National Groundwater Monitoring Network) were carried out to evaluate the characteristics of groundwater level change in Korea and to prevent groundwater hazard due to water level decline. Most of monitoring wells showed depth to water within 2~10 m and water level variation less than 6 m. Monitoring wells located in the bedrock aquifer has deeper water level and larger variation than the alluvial aquifer. Long-term monitoring data were classified into 24 types of water level fluctuation by analyzing time series data. First, all of monitoring wells are classified into 6 types: seasonal, impulse, constance, ramp, inclination and step. Then two factors such as sensitivity to rainfall (sensitive or insensitive), effect of pumping at neighboring well (affected or not)) were applied to each type for more detailed classification. The results showed that seasonal type occupied 66.8% of the whole monitoring wells, impulse 12.4%, constance 11.8%, ramp 4%, inclination 3.2%, and step 1.7%, respectively. Additionally 72.5% of monitoring wells were sensitive to rainfall and 24.6% were affected by pumping at neighboring well. From linear regression analysis of long-term monitoring data, 3.4% of the whole monitoring wells showed upward trend of water level (annual rate of water level increase was more than 0.05 m/year), and 14.7% showed downward trend (annual rate of water level decrease was more than 0.05 m/year). The results of monthly percentile box-plot showed that water level of 9.8% of the whole monitoring wells was rising, and 26.3% was descending. On the basis of result of analyses, the site selection standard which needs to be investigated for preventing groundwater hazard caused by water level change was proposed.

PartⅡ Hydrogeochemistry of groundwater from National Groundwater Monitoring Network, Korea

Analysis of groundwater quality characteristics of Korea was carried out using hydrochemical data of NGMN. Groundwater of Korea can be classified into 6 type according to the hydrochemical characteristics by Stiff and Durov diagram as follows 1) Low TDS, Low Nitrate, Ca-HCO3 type, 2) High TDS, High Nitrate, Ca-Cl(SO4) type 3) High TDS, Highest Nitrate, Ca(Na)-Cl(SO4) type, 4) Low TDS, Low Nitrate, Na-HCO3 type, 5) Highest TDS, Na-Cl type, 6) Highest TDS, Ca-SO4 type. Kruskal?Wallis Hypothesis test result showed that there is no hydrogeochemical differences between bedrock and alluvial aquifer, and this implies that groundwater quality of bedrock aquifer originate from not long-time circulation within bedrock but mixing of shallow groundwater. Three principal components with accounted for 53% of the variability were extracted and each PCs can be explained as 1) anthropogenic influence, 2) water-rock interaction, 3) oxidation-reduction reaction respectively. The result of K-means cluster analysis showed that groundwater of Korea can be classified into 5 groups as follows 1) affected by anthropogenic activity group, 2) affected by water-rock interaction group, 3) less affected by anthropogenic activity group, 4) affected by anthropogenic activity group but decrease in nitrate due to reduction condition, 5) recently recharged group having reduction condition. SOM(Self Organizing Maps) analysis suggests 6 group and determined as useful tool for clustering of regional and multi-dimensional data. The result of Kruskal?Wallis test of nitrate concentration showed that aquifer depth, land use, water level and altitude of well affect nitrate concentration.