Graduate Institute of Applied Geology, National Central University, Taoyuan City, 32001, Taiwan.
Center for Environmental Studies, National Central University, Taoyuan City, 32001, Taiwan.
Environ Monit Assess. 2019 Jan 18;191(2):83. doi: 10.1007/s10661-019-7199-4.
This study employed experimental and numerical methods to assess the behavior of conservative solute transport for a selected temporary solid waste site in a reclamation area in western Taiwan. Calibrating a site-specific numerical model, finite element model of water flow through saturated-unsaturated media (FEMWATER), relies on observations from field- and laboratory-scale hydraulic tests and spatial-temporal monitoring. The field-scale experiment used a modified hydraulic tomography survey (MHTS) to identify near surface aquifer stratifications and estimate the distribution of saturated hydraulic conductivity. The pressure plate experiments provided parameters for the van Genuchten soil characteristic model. Sensitivity analyses were then conducted based on varied recharge rates and dispersivities applied to the calibrated model. Observations of groundwater levels and salinity in the wells indicated that the regional groundwater flow was from southeast to northwest. In addition, a shallow freshwater layer was noted in the study area. The tidal-induced amplitudes for water level fluctuation in the wells ranged from 2 to 20 cm, depending on their distance from the seawater body. MHTS showed clear stratification, similar to that of well loggings at the storage site. The hydraulic conductivity at the test site ranged from 8 to 10 m/day, which is close to that obtained from the laboratory falling head test. The results of particle-tracking modeling showed that the critical recharge rate for the site needed to enhance plume traveling is 1000 mm/year. The increase in dispersivity values induced a decrease in plume travel time of up to 1000 days from the site to the coastal line. A special case for pulse releasing solute at the site shows that the key factor in controlling plume migration is the recharge rate. This is due to the low natural head gradient in the reclamation area. The results therefore suggest that a land drainage system near the site can play an important role in contaminant transport in the reclamation area.
本研究采用实验和数值方法，评估了台湾西部一个填海区选定的临时固体废物场保守溶质运移行为。为了校准特定于场地的数值模型，饱和-非饱和介质水流的有限元模型（FEMWATER），依赖于现场和实验室尺度水力测试和时空监测的观测结果。现场尺度实验采用改良水力层析成像调查（MHTS）来识别近地表含水层分层，并估计饱和水力传导率的分布。压力板实验为 van Genuchten 土壤特征模型提供了参数。然后，根据应用于校准模型的不同补给率和弥散率进行了敏感性分析。地下水水位和井中盐分的观测表明，区域地下水从东南向西北流动。此外，研究区域还存在一个浅层淡水层。井中水位波动的潮汐诱导幅度取决于它们与海水体的距离，范围从 2 到 20 厘米。MHTS 显示出明显的分层，与储层的测井记录相似。测试现场的渗透系数范围为 8 到 10 米/天，接近实验室降落头试验获得的值。粒子跟踪建模的结果表明，增强羽流传播所需的场地临界补给率为 1000 毫米/年。弥散率值的增加导致羽流从场地到海岸线的传播时间减少了长达 1000 天。在场地释放脉冲溶质的特殊情况下，控制羽流迁移的关键因素是补给率。这是由于填海区的自然水头梯度较低。因此，研究结果表明，场地附近的土地排水系统在填海区的污染物运移中可以发挥重要作用。
