Wijewardana Y N S, Shilpadi A T, Mowjood M I M, Kawamoto K, Galagedara L W
Uva Wellassa University, Badulla, Sri Lanka.
Department of Agricultural Engineering, University of Peradeniya, Peradeniya, Sri Lanka.
Environ Monit Assess. 2017 Feb;189(2):57. doi: 10.1007/s10661-017-5770-4. Epub 2017 Jan 13.
The assessment of polluted areas and municipal solid waste (MSW) sites using non-destructive geophysical methods is timely and much needed in the field of environmental monitoring and management. The objectives of this study are (i) to evaluate the ground-penetrating radar (GPR) wave responses as a result of different electrical conductivity (EC) in groundwater and (ii) to conduct MSW stratification using a controlled lysimeter and modeling approach. A GPR wave simulation was carried out using GprMax2D software, and the field test was done on two lysimeters that were filled with sand (Lysimeter-1) and MSW (Lysimeter-2). A Pulse EKKO-Pro GPR system with 200- and 500-MHz center frequency antennae was used to collect GPR field data. Amplitudes of GPR-reflected waves (sub-surface reflectors and water table) were studied under different EC levels injected to the water table. Modeling results revealed that the signal strength of the reflected wave decreases with increasing EC levels and the disappearance of the subsurface reflection and wave amplitude reaching zero at higher EC levels (when EC >0.28 S/m). Further, when the EC level was high, the plume thickness did not have a significant effect on the amplitude of the reflected wave. However, it was also found that reflected signal strength decreases with increasing plume thickness at a given EC level. 2D GPR profile images under wet conditions showed stratification of the waste layers and relative thickness, but it was difficult to resolve the waste layers under dry conditions. These results show that the GPR as a non-destructive method with a relatively larger sample volume can be used to identify highly polluted areas with inorganic contaminants in groundwater and waste stratification. The current methods of MSW dumpsite investigation are tedious, destructive, time consuming, costly, and provide only point-scale measurements. However, further research is needed to verify the results under heterogeneous aquifer conditions and complex dumpsite conditions.
在环境监测与管理领域，采用非破坏性地球物理方法评估污染区域和城市固体废物（MSW）场地既及时又非常必要。本研究的目的是：（i）评估由于地下水中不同电导率（EC）导致的探地雷达（GPR）波响应；（ii）使用可控渗滤计和建模方法对城市固体废物进行分层。利用GprMax2D软件进行了探地雷达波模拟，并在两个分别填充沙子（渗滤计 - 1）和城市固体废物（渗滤计 - 2）的渗滤计上进行了现场测试。使用带有200 MHz和500 MHz中心频率天线的脉冲EKKO - Pro探地雷达系统收集探地雷达现场数据。研究了在向地下水位注入不同电导率水平的情况下探地雷达反射波（地下反射器和地下水位）的振幅。建模结果表明，反射波的信号强度随着电导率水平的增加而降低，并且在较高电导率水平（当EC>0.28 S/m时）地下反射消失且波幅降至零。此外，当电导率水平较高时，羽流厚度对反射波的振幅没有显著影响。然而，还发现，在给定的电导率水平下，反射信号强度随着羽流厚度的增加而降低。潮湿条件下的二维探地雷达剖面图像显示了废物层的分层和相对厚度，但在干燥条件下难以分辨废物层。这些结果表明，探地雷达作为一种具有相对较大样本体积的非破坏性方法，可用于识别地下水中含有无机污染物的高度污染区域以及废物分层。目前城市固体废物倾倒场调查方法繁琐、具有破坏性、耗时、成本高，且仅提供点尺度测量。然而，需要进一步研究以验证在非均质含水层条件和复杂倾倒场条件下的结果。
