Simulating Fate and Hydrogeochemical Transport of Arsenic in Beitou-Guandu Area
| Autor: | Chin-Jen Wang, 王勁壬 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 High arsenic (As) concentration of Beitou geothermal spring was up to 4,600 μg/L, and downstream Guandu Plain and Guandu Wetland may be affected by the movement of As, via the stream and groundwater flow. However, the distribution and hydrogeochemical processes of As from geothermal spring water to downstream of groundwater and Guandu Wetland were not well known. The purpose of the study is to assess the probable pathways (stream and groundwater flow) of As and evaluate fate and transport of As in Beitou-Guandu area. Firstly, the groundwater head and flow directions are simulated in this study area by using HYDROGEOCHEM- fluid flow model. The steady groundwater flow model is well-calibrated with the root mean square error (RMSE) 1.73 m and the R2 0.992. The simulated hydraulic head varies with terrain topography and the groundwater from the Beitou geothermal valley gradually move to the downstream of Guandu Wetland. Secondly, the As concentrations in the downstream river mouth area simulated by 1-Dimension PHREEQC of cases 1 (stream path) and 2 (groundwater flow path) are 0.0042 and 7.45 μg/L, respectively. However, the As concentration of river mouth area was 3 μg/L as observed value of EPA, which compared with results of two cases, the groundwater flow path (case 2) was the dominant advective-transport mobility of As. The major retarded mechanisms of As mobility in case 1 simulation were the surface adsorptions of the iron oxide minerals. Moreover, the major mechanism of As advective-transport mobility in case 2 governed by the adsorption reactions of iron oxide/ iron sulfide minerals. Thirdly, the spatial-temporal distributions of As in Beitou-Guandu area are simulated by the HYDROGEOCHEM - reactive transport model. The result shows that As concentration (>250 μg/L) in groundwater of Guandu Plain was caused by the movement of high As concentration from the Beitou geothermal spring water. In contrast, the low As concentration (5-50 μg/L) in Guandu Wetland was caused by the tidal water dilution. The simulated As concentrations increase in the first 3 years, then gradually decrease due to the adsorption of As on the iron oxide minerals and iron sulphide minerals. Fouthermore, the hydrogeochemical transport model is then applied to assess two scenarios including the effect on the mangrave plants of Guandu Wetland, and the application of groundwater development for adapting the climate change. For scenario 1, the dominant mangrove plants, Kandelia obovata, which can reduce about 5- 30 μg/L As concentration of groundwater. It may be one of the sinks of As in Beitou-Guandu area. For scenario 2, the application of permissible amount of groundwater withdrawn may speed up the As mobility in the downstream Guandu Plain. The result shows that As concentrations in northern Guandu Plain may increase about 200 μg/L. However, the As concentrations in Guandu Wetland are little affected. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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