The purpose of this study is to investigate the cause of groundwater contamination in the selected study areas and to propose the appropriate management plans for the drinking shallow groundwater in agricultural areas. The study areas were selected in 2014 and 2015 with consideration of the groundwater quality, field survey and hydro(geo)logical factors. For five years(2014-2018), we have been monitoring the groundwater quality, analyzing the hydrogeological characteristics, and investigating on-site contaminant sources in the study areas.
In the study area 1, the organic fertilizer used in the field was investigated as the main source of groundwater contaminants. We have managed the use of organic fertilizer since 2016 and installed the new groundwater wells in the weathered vadose zones and weathered rock layers to improve the groundwater quality and supply the safe groundwater. The result showed that high NO3-N (>20 mg/L) concentrations in some wells have decreased with time. However, the contaminant concentrations of the newly installed groundwater wells showed no significant variations during the study period. It implies that the shallow aquifers have been heavily contaminated by the non-ponit contaminant sources mainly located in the vadose zones.
In the study area 2, the groundwater deterioration was investigated by the excessive use of organic fertilizer and livestock manure accumulated throughout the field. Relatively deep-groundwater wells (approximately 100 m drilled from the ground surface) and direct groundwater supply system were proposed and applied to provide the safe and drinkable groundwater in 2016. In order to analyze the characteristics of groundwater quality changes after removing the point contaminant source of livestock manure in October 2017, the monitoring wells were installed in the downstream direction of groundwater flow from the point sources. Despite of removing the point sources, the NO3-N concentration of monitiong wells showed no significant variations. The contaminant concentrations, however, increased when the groundwater level rose in the study area. Therefore, more time to monitor is needed to evaluate the test bed for the point source control.
As the result of this study, various action plans such as (non) point contaminant source controls and so on, are needed for improving groundwater quality. This whole process should be performed by the comprehensive management plans, which are based on evaluating and estimating groundwter quality status and characterizing the detailed hydrogeological setting in the agricultural study area, and so forth.