原台灣金屬鑛業公司所屬煙道區逕流對承受水體砷污染之影響評估

The impact of surface runoff near wasted gas tunnels on the arsenic pollution of receiving waters at a contaminated abandoned copper mine and refinery site in Chinkuashih, Taiwan

賴允傑(Yun-Jie Lai)

指導教授 ： 吳先琪

國立臺灣大學/工學院/環境工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.01854

摘要

原台灣金屬鑛業公司濂洞煉銅廠所屬三條廢煙道已於露天環境下破損棄置近40年，且經分析確認殘存於廢煙道內之煙道碴與煙道周邊受污染土壤均含有高濃度之砷，然該區域歷年之環境影響調查均未評估污染物可能受土壤沖蝕及地表逕流影響下之污染情形，以及對承受水體之影響。本研究以序列萃取方式探討現場廢煙道內及附近之土壤中砷之化學型態特徵，運用地理資訊系統軟體及通用土壤流失公式估算區域之地表逕流量及土壤流失量，進而推估地表逕流中之砷濃度，最後則以研究區域採集之水樣砷濃度比較承受水體影響程度推估結果。以Wenzel序列萃取法分析煙道碴及受污染土壤砷濃度之結果顯示，70%以上之總砷含量均屬無定形與結晶性水合鐵鋁氧化物之結合態，3∼30%為樣品表層之特異性或非特異性吸附態，殘餘態之比例僅佔1∼5%。根據BCR序列萃取法醋酸萃取砷濃度結果顯示具移動性或潛在環境危害之砷含量最高應不超過總量之30%，並隨風化程度由低至高遞減。廢煙道周邊地區受污染範圍約25.8公頃，利用地理資訊系統軟體空間分析功能及通用土壤流失公式估算每年每公頃之土壤流失量約為95公噸，換算污染區全區每年平均流失2,400噸土壤，其中83%流入濂洞溪流域，其餘則流入濂洞煉銅廠或樂利橋集水區。經模擬推估污染區每年因土壤流失所輸出之含砷污染物總量約為5.4公噸，以土壤平均濃度推估地表逕流中砷濃度平均值最高約為3.11 mg/L，與所屬集水區內未受污染之地表逕流匯流後會增加承受水體砷濃度1.28 mg/L。於廢煙道周邊實測採集之地表逕流水樣砷濃度值為1.5 mg/L，有煙道之集水（污）區地表逕流砷濃度平均值則介於0.2∼0.5 mg/L，由於水樣中砷濃度多為溶解態，應為煙道碴及受污染土壤於酸性環境下溶解釋出之砷，由雨水挾帶於土壤表面漫流或入滲至土層中以中間流之型式流出之地表逕流，與依據土壤沖蝕量推估產生之顆粒態砷濃度不同，故不合適以模式推算之濃度值直接比較。本研究之結果說明煙道碴及受污染土壤因風化程度不同以致砷濃度相態分佈之差異性，詳細估算廢煙道周邊地區受污染土壤沖蝕情形以及污染物輸出量，以及綜合探討地表逕流對承受水體之影響，可提供此污染區環境危害評估及風險管理之參考。

關鍵字

砷 ； 土壤污染 ； 地表逕流 ； 廢煙道 ； 土壤重金屬型態 ； 土壤流失 ； 金瓜石 ； 台灣金屬鑛業公司

並列摘要

There are three 40-years-old wasted gas tunnels in the abandoned Taiwan Metal Mining Corporation (TMMC) complex in Chinkuashih, New Taipei City, Taiwan. It was found that the residue in the gas tunnels or the soil near the tunnels contained high concentration of arsenic. However, in the field survey and pollution impact assessment conducted in the past, the impact on the water quality of receiving waters by soil erosion or surface runoff was not assessed. In this study, sequential extraction was used to characterize the speciation of arsenic in soils, the surface runoff and soil loss quantity were estimated with the assist of global information system (GIS) and universal soil loss equation (USLE), and the arsenic concentration in the surface runoff was estimated. Surface runoff and receiving water in the study area were also collected and analyzed to compare to the simulation results. The results of the sequential extraction analyses indicate that more than 70% of arsenic is in the forms of amorphous and crystalline hydrous Fe/Al bound speciation, 3 to 30% is non-specific or specific bound arsenic speciation on the sample surface, only 1 to 5 % is residual form in the waste and soil samples. According to the results of BCR sequential extraction, no more than 30% of arsenic can be regarded as the most easily mobilizable arsenic fraction from acetic acid extraction procedure, and is lower for samples subject to longer weathering time. The total contaminated land in this site is estimated about 25.8 hectare. 95 tons of soil is lost per hectare per year, that is 2,400 tons of polluted soil lost for this contaminated site estimated by GIS and USLE calculation. The loading of arsenic from soil erosion is about 5.4 tons each year. The predicted arsenic concentration in the surface runoff would be 3.11 mg/L in the polluted area, and be diluted to 1.28 mg/L with non-polluted surface runoff from the catchment. Arsenic concentration of surface water runoff collected near waste gas tunnels is 1.5 mg/L, whereas the average concentration is only 0.2 to 0.5 mg/L for the contaminated catchment. Most of the arsenic in the water sample is in dissolved form, which might be released from the gas tunnels waste and polluted soil due to acidic leachate, then entrained by surface water flows or intermediate flow downgradient. The dissolved load contributes more to the arsenic concentration in the receiving waters than the particulate arsenic from the soil impacted by raindrops and mobilized by surface water runoff. The USLE is not suitable to estimate the concentration of arsenic in runoff in very acidic soil condition as the soil in this site. Therefore, it is not suitable to compare the arsenic concentration of water samples directly to the simulation results. The arsenic speciation of gas tunnel waste and polluted soils with different weathering condition were revealed. The amount of soil eroded and pollutants exported from the polluted area have been investigated and the impact of surface runoff near wasted gas tunnels on the water quality of receiving waters was estimated. The results can provide valuable information for the environmental hazardous assessment and risk management of this contaminated abandoned copper mine and refinery site in Chinkuashih, Taiwan.

並列關鍵字

arsenic (As) ； soil pollution ； surface runoff ； waste gas tunnel ； soil heavy metal fractionation ； soil errosion ； Chinkuashih ； Taiwan Metal Mining Corporation (TMMC)

參考文獻

12. 林俐玲，2010，通用土壤流失公式(USLE)之應用與誤用，水保技術5:119-121。

21. 新北市政府環境保護局（原臺北縣政府環境保護局），2010b，99年4月9日北環水字第0990028943號公告。

26. 簡耀鴻、張東炯、王兆印，2008，在不同空間解析度的DEM提取坡度的研究－以烏山頭水庫地區為例，農業工程學報54:1-8。

13. 金翁正，1996，金瓜石-濂洞溪砷的來源傳輸過程和去處，國立臺灣大學海洋研究所碩士論文。

28. Agency for Toxic Substances and Disease Registry (ATSDR). 2007. Toxicological Profile for Arsenic. U.S. department of health and human services. Atlanta, Georgia.