Groundwater is one of the major sources for supplying daily usage water of residents, especially in Changhua and Yunlin areas. However, the contaminants, such as Fe, Mn and heavy metals, are still major issues in the coming years. These pollutants are generally recognized as being released by natural soils due to the water-rock interaction. Although there have been many studies addressing on the interaction between groundwater and host soil, some topics still need more effort to get a better approach. In this study, a concept of natural tracer will be utilized to establish the water chemical model. Some ultra-trace metal elements, such as rare earth elements, are very suitable to be the natural tracers. The bulk chemistry of soil is highly controlled by the ratio of sand to clay, which is equivalent to the ratio of quartz to clay mineral. Therefore, the relative concentrations of pollutants should be evaluated after the effect of sand-clay ratio is normalized. Moreover, the groundwater chemistry represents the result of long-term reaction with soils. The studied area should be extended to the upstream along the groundwater flow path.

Tsengwenshi Watershed;Groundwater Pollution;Sequential Extraction Procedure