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Outline
To accurately characterize the impact on DNAPL contaminant migration under the background of groundwater level rise in the coastal areas of North China in recent years, a case study was conducted at a NAPL contaminated site in Tianjin. Utilizing the multiphase flow numerical model TOUGH/TMVOC, a simulation was constructed to analyse the migration characteristics of DNAPL in both homogeneous and layered heterogeneous media under varying groundwater levels. The focus of the study was on the variation of DNAPL movement above and below the water table interface. The key findings were as follows: the NAPL phase was the primary form in which DNAPL migrates in groundwater. In homogeneous saturated media, DNAPL migration exhibited both vertical infiltration and horizontal diffusion. In the unsaturated-saturated aquifer system, a significant increase in DNAPL saturation was observed below the water table interface, with an increase of 47.5% compared to the initial leakage stage. Under water level recovery conditions, the phenomena of sudden increases in DNAPL saturation and vertical migration of contaminants were weakened, with the extension rate decreasing by 1.5~1.8 times compared to low water levels; simultaneously, the phase change of dissolved components to gaseous state was inhibited, resulting in reduced amount of gas phase DNAPL. The dynamic changes in the water table, in conjunction with the layered heterogeneous stratum structure, jointly regulated the DNAPL migration process. Low-permeability layers impeded DNAPL migration. Although DNAPL saturation increased after crossing the water table, its maximum saturation still decreased by 6%~7% compared to the saturated conditions, and the mass of contaminants decreased by 13%~15%. It is recommended to implement contaminant interception when DNAPL reached minimum saturation near the water table to improve remediation efficiency.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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