屏東沿海地區地下水水質之鹽化趨勢

Abstract

The chemical compositions of groundwater, sampled from 18 built-up observation wells located in Pingtung area, were analyzed in 1998 for assessing the groundwater quality. As compared the groundwater qualities with the previous study, it is suggested that the salinization of shallow groundwater is alleviated and that of deep groundwater seems to be more severe than before. This may be due to the change patterns in the utilization of pumping groundwater. The results also showed that there were distinctive distributions of three hydrochemical facies if tested water qualities were constructed in a Piper diagram. Ca-HCCh type water, with distribution apparently in the midstream and upstream areas, is formed by the chemical interaction between groundwater and the aquifer materials. Na-Cl type water, with distribution along the coastal area, is mainly related to the encroachment of seawater caused by the intensive exploitation of groundwater. Ca-Cl type water, with distribution between the Ca-HC03 type and Na-Cl type zone, is developed when the intruded seawater forced through the fresh aquifer. Analyzing the water quality and hydrochemical facies of groundwaters indicate the active seawater intrusion is in processing in coastal Pingtung Plain especially in deeper aquifer. 本研究分析經濟部所轄屛東平原地區18口地下水分層水位觀測井之水質，配合分層採樣分析結果並與79或84年度之檢測資料比較，顯示沿海地區的淺層地下水之鹽化有舒緩、而深層地下水之鹽化卻有加劇的現象，這可能是因爲抽水利用型態的改變所導致。從Piper水質菱形圖的分析， 本區地下水之水化學相有三區之分布：(一)Ca-HCO3型之地下水主要分布在中、上游地區，主要爲含水層中造岩礦物基質受碳酸之溶解作用造成；(二)Na-a型之地下水全都分布在臨海之沿岸地區，是受海水入侵污染所造成；(三)Ca-Cl型水質分布之區域處於Ca-HC03型與Na-Cl型之間，其代表海水正侵入淡水層的過程，整體而言屛東平原地區之地下水現階段爲一淡水含水層受海水侵入的狀況，而以深層含水層較爲嚴重。