Laboratory and Field Measurements of Soil Water content and Contaminant Concentration Using Time Domain Reflectometry

• Main Authors: Hsu, Shu-Chi, 許書齊
• Other Authors: Chiu, Yung-Chia
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/57781012859979005763

碩士 === 國立臺灣海洋大學 === 應用地球科學研究所 === 102 === As industry develop rapidly, the issues of environmental pollution increase drastically as well. When contaminants infiltrate into soil and groundwater, the distributions of contaminant are affected by geometries of the soil, aquifer properties, mechanisms of solute transport, and boundary conditions. However, these factors include many uncertainties and result in the challenges during the contaminant remediation. In order to enhance the ability for contaminated site remediation, acquiring accurate understandings of the unsaturated zone of a groundwater flow and the contaminants concentrations will be the primary task. As widespread use of geophysical approaches, time domain reflectometry （TDR）, a non-destructive geophysical approach, is selected as the technique to measured soil water contents and contaminant concentrations in this study. TDR determines the soil water content and bulk electrical conductivity （EC） by analyzing the waveform and amplitude of reflected electromagnetic wave between different media. A series of laboratory experiments are conducted in homogeneous and layered media to investigate the fundamental theory of TDR, and the relations between reflected waveforms and soil water content are evaluated. Combining the use of TDR and tensiometer, the water retention curve can be detailed delineated, and the effect of hysteresis can also be obtained through repeated processes of wetting and drying in soil. When using TDR to measure EC, the accuracy can be improved by considering the energy loss resulted from the resistances of coaxial cable and multiplexer. The individual calibration of geometric constant of probe before taking measurement can also be conducted to increase its accuracy. In this study, TDR has been verified to have the capability of estimating contaminant concentration accurately in real-time through the relations of bulk electrical conductivity, water electrical conductivity, and contaminant concentration. Besides, the TDR probe is modified to overcome the underwater measurement and applied to a contaminated site with mercury contaminated sediments. The results from field experiments show that although the absolute concentrations cannot be identified, the spatial distribution of concentration can be differentiated clearly. In this study, TDR is demonstrated as a reliable tool for contaminated site investigation and site remediation assessment.