台灣中部地區地下水水質特性分析

Abstract

台灣中部地區的濁水溪沖積扇為地下水補注量最充沛的區域，近來因為地下水超抽情形嚴重，因而造成水質惡化的情形。本研究利用三種分析方法進行中部地區地下水水質特性分析，以進一步找出代表性污染因子。以因子分析中部地區地下水，其中以「鹽化因子」為主要代表因子，其餘因子尚有「氮污染因子」、「有機性污染因子」及「礦物性因子」。 以Stiff水質形狀圖分析中部地區地下水，以Ca2+、HCO3-離子凸出型佔最多比例，Ca2+、SO42-離子凸出型佔次多比例。Piper水質菱形圖分析中部地區地下水，以I區佔最多比例，V區次之，顯示中部地區地下水水質尚稱良好。苗栗及彰化、雲林地區的沿海區域，部份地下水監測井分析結果顯示，已被海水影響有鹽化現象。將離子強度與導電度、總溶解固體進行迴歸分析，所得結果與文獻相同。統計中部地區地下水中總溶解固體與導電度比值為0.69 ± 0.11，可代表中部地區地下水水質特徵。 整體而言，中部地區地下水水質尚稱良好，惟於部份沿海區域水質已有鹽化現象，必須持續監測。由本研究所得地下水代表性污染因子，可提供地下水污染防治的參考。

The alluvial fan of Jhuoshuei River in central Taiwan is a known recharged area with adequate groundwater. It is a serious issue that groundwater could be pumped to make up the shortfall, maybe it is the reason why groundwater quality became worse recently. Three approaches to investigate ground water quality in central Taiwan have been applied in order to further establish the index of water quality. First, we have analyzed groundwater quality in central Taiwan area by factor analysis, the data showed that salinization factor could be the major factor. And other factors include nitrogen pollution factor, organic pollution factor and mineral factor. Second, the ions-related data showed that groundwater quality is fine. The most classified type of Stiff diagram is a combination of calcium ion and hydrogen carbonate, the next is a combination of calcium ion and sulfate; Piper diagrams has showed the most type is Type-I, the next is Type-II. Results of some monitor wells in coasting area of Miao-li, Chang-hwa and Yun-lin have showed that salinization may be caused by sea water. Third, regression data of ion strength, conductivity and total dissolved solids (TDS) seems the same as reference. The ratio of TDS to conductivity is 0.69 ± 0.11, it could present the characteristics of groundwater quality in central Taiwan. Overall speaking, groundwater quality in central Taiwan is quite good except for the salinization of groundwater in some coasting area. We suggest that the administrative agency has to keep monitoring for a long term. Eventually, representative groundwater pollution factors found from this study could provide as a reference for the pollution prevention and control of groundwater.