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  • 學位論文

應用多變量統計技術歸納蘭陽平原地下水中砷釋出機制

Analyzing the Mobilization Mechanism of Groundwater Arsenic in Lanyang Plain Using Multivariate Statistical Techniques

指導教授 : 劉雅瑄
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摘要


臺灣自早期便因烏腳病的出現而使地下水中砷的議題廣受討論,在蘭陽平原同樣也多有地下水砷濃度超標的問題。為釐清蘭陽平原各個地下水文條件不一之地區何以具有較高砷濃度,本研究自行政院環保署全國環境水質監測資訊網提取西元1993-2020年共28年的蘭陽平原地下水水質監測紀錄,以期透過長時間且穩定的監測資料觀察區域的水質特性,並發掘其與砷釋出機制之關係。   本研究以常年監測記錄為基礎,利用比例法進行資料前處理,轉化數據分佈並優化多變量分析之分析效益。而後使用多變量統計方法的主成份分析(Principal Component Analysis, PCA)及聚類分析(Clustering Analysis, CA)進行資訊統整,以歸納並解釋蘭陽平原各區域的水質特性及變化。根據分析結果,蘭陽平原之地下水井可分為五群:A群受鹽化影響而有高濃度氯離子;B群位於平原東部的還原性環境及人類活動影響區域;C群水質與B群同樣有還原性條件及人類活動影響,但強度較弱;D群為受農作肥料影響的扇頂農盛區;E群分佈於山麓帶及蘭陽溪岸,接收新鮮水源而呈氧化性環境。   在蘭陽平原各類地下水水質中,A群及B群的井位與高砷地下水關係最大,C群次之。A群有氯離子與砷競爭吸附而導致砷被釋出,以受古海水殘留影響的冬山國小舊井為代表性井位,古亭國小井也曾因現生海水之影響而相同結果。B群井位分布於蘭陽平原東部,地層因泥層阻礙通氣及人類活動污染而有強烈的還原性環境,宜蘭高商井、竹林國小井及古亭國小井皆因此而有砷之還原性溶解機制。同屬B群之冬山國小新井則位於山麓帶,但因鄰近工廠清倒重油等廢棄物後累積於泥質沉積層所致之還原性環境而同樣有砷的還原性溶解機制。員山國小井數據多屬於C群,受人類污染影響較小而以源自四稜砂岩之矽酸鹽競爭吸附為砷釋出的主要機制。由此可見,蘭陽平原地下水中砷富集機制在各處不盡相同,包含還原性溶解機制及競爭吸附機制,而無氧化性溶解機制。

並列摘要


The arsenic in groundwater has been a serious issue and widely discussed in Taiwan because Blackfoot Disease was prevalent back in 1950s. Lanyang Plain is one of the regions where has most severe arsenic issue. However, to understand the source of arsenic is difficult due to the geohydrological siting in each area of the Lanyang Plain is different. In order to clarify the formation of the high concentrated arsenic in groundwater of the Lanyang Plain, this study analyzed monitoring records of groundwater quality during 1993~2020 prevented by Environmental Protection Agency, Taiwan (EPA). Based on 28 years of long-term and stable monitoring, we tried to depict water characteristics of this area and establish the mechanism of the mobilized arsenic in the Lanyang Plain. The “proportional method” was used for data pre-processing. Then, the Principal Component Analysis (PCA) and Cluster Analysis (CA) were applied to classify the groundwater characteristic and driving factor of groundwater quality in each region of Lanyang Plain. According to the results of PCA and CA, the Lanyang Plain can be divided into five groups. The arsenic releasing in Group A is caused by competitive adsorption of chloride triggered by salinization. For example, GuTing well was affected by the modern seawater intrusion, and DongShan-1 well was intruded by paleo-seawater. In Group B, arsenic is released due to the reductive dissolution mechanism which is deeply affected by geological structure and human activities in the east of the plain (GuTing well, YiLanGaoShang well and ZhuLin well). In addition, the reduction environment in DongShan-2 well was caused by the accumulation of heavy oil and other chemical pollutions from adjacent factories and thus, caused arsenic releasing into groundwater by the reductive dissolution mechanism. Arsenic releasing process in Group C is similar with group B, but the strength of mechanism is weaker than Group B. However, the main driving factor of arsenic releasing would change to competitive adsorption mechanism when these two factors are in parallel. The Group C can be found in YuanShan well where silicate provided by the Szeleng Layer caused competing adsorption with arsenic. In conclusion, this study classifies the groundwater characteristic of Lanyang Plain into five groups and identify the two arsenic releasing mechanisms. The main mechanisms of arsenic releasing are “reductive dissolution mechanism” and “competitive adsorption mechanism”.

參考文獻


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