水位波动下包气带透镜体影响LNAPL迁移的数值模拟研究

潘明浩; 时健; 左锐; 赵晓; 刘嘉蔚; 薛镇坤; 王金生; 胡立堂

doi:10.16030/j.cnki.issn.1000-3665.202105027

水位波动下包气带透镜体影响LNAPL迁移的数值模拟研究

1.
北京师范大学水科学研究院，北京　100875

2.
地下水污染控制与修复教育部工程研究中心，北京　100875

基金项目: 国家自然科学基金项目（41877181；41831283）；111引智项目（B18006）

详细信息

作者简介: 潘明浩（1998-），男，硕士研究生，主要从事地下水污染研究。E-mail：202021470021@mail.bnu.edu.cn

通讯作者: 左锐（1981-），男，博士，教授级高工，主要从事地下水污染控制与修复研究。E-mail：zr@bnu.edu.cn

中图分类号: P641.2

收稿日期: 2021-05-18

修回日期: 2021-07-06

刊出日期: 2022-01-15

A numerical simulation study of the effect of the vadose zone with lenses on LNAPL migration under the fluctuating water table

1.
College of Water Sciences, Beijing Normal University, Beijing　100875, China

2.
Engineering Research Center of Groundwater Pollution Control and Remediation, Ministry of Education, Beijing　100875, China

More Information

Corresponding author: ZUO Rui, zr@bnu.edu.cn

Received Date: 18 May 2021

Revised Date: 06 July 2021

Publish Date: 15 January 2022

摘要

摘要:
轻质非水相液体（LNAPLs）在土壤包气带中具有多相态特征，非均质性、地下水位波动等因素将显著增加包气带内LNAPLs污染的复杂程度。已有研究多关注于揭示包气带内自由相LNAPLs的污染过程，少有更为深入地探究水位波动时非均质结构对LNAPLs迁移及各相态分布规律的影响。基于TOUGH2程序构建包气带多相流数值模型，以揭示透镜体结构与地下水位波动共同作用下LNAPLs迁移过程及相态分布。研究结果表明：（1）含水率变化是LNAPLs迁移分布的主要控制因素，包气带内受透镜体介质岩性、水位波动影响所呈现的含水率变化直接控制LNAPLs迁移规律及分布特征；（2）水位恒定时，细砂透镜体使LNAPL呈“蓄积穿透-横向扩展-绕流”迁移，粗砂透镜体则是LNAPL垂向迁移的“优势通道”，水位波动引起的细砂透镜体含水率变化使“绕流”显著增强，粗砂透镜体则进一步呈现“优势空间”作用；（3）水位恒定时，细砂透镜体模型中LNAPL滞留于透镜体内部，粗砂模型中LNAPL则集中于透镜体下方，水位波动下透镜体附近LNAPL分布范围扩展，两模型LNAPL分布面积较水位恒定时分别增大51%、63%；（4）两模型中LNAPL挥发通量均呈“先减小-后增大”规律，并受LNAPL-气体接触条件及LNAPL分布状况共同作用，水位波动打破三相平衡状态，主要表现为水位抬升阶段LNAPL挥发增强，此时两模型中平均挥发量较水位恒定时增大124%～126%。研究为非均质石油污染场地中的LNAPL污染过程认识提供了科学的理论依据。
- 轻质非水相液体 /
- 包气带 /
- 非均质性 /
- 数值模型
Abstract:
Light Non-Aqueous Phase Liquids (LNAPLs) in vadose zone is of multi-phase characteristics, while factors such as heterogeneity and groundwater fluctuation are expected to significantly increase the complexity of LNAPLs contamination in vadose zone. Previous studies have mostly focused on revealing the contamination process of free-phase LNAPLs, few have explored deeply the influence of the heterogeneous structure on the migration and phase distribution pattern of LNAPLs when the water table fluctuates. A numerical model of multiphase flow in vadose zone is established based on TOUGH2 to reveal the migration and phase distribution of LNAPLs under the joint effect of different lithological lenses and water table fluctuation. The results show that (1) the migration and distribution regularity of LNAPLs in vadose zone is predominantly controlled by the variation in water content, which is presented under the effect of heterogeneity and water fluctuation. (2) In the steady groundwater scenario, LNAPL migrates in an “accumulation-lateral expansion-flow bypass” pattern around the fine-sand lens, while the coarse-sand lens acts as the "preferential route" for the vertical movement of LNAPL. Flow around the fine-sand lens is significantly enhanced by the variation in water content induced by groundwater fluctuation, and the coarse-sand lens further exhibits the "preferential space" effect. (3) When the water table is steady, LNAPL are concentrated inside and below the lens body in the fine-sand and coarse-sand lens models, respectively. In the fluctuating groundwater scenario, a greater range of LNAPL is presented in the vicinity of the lens with the distribution area in each model is 51% and 63% larger than that in the steady scenario. (4) Volatile flux of LNAPL, affected by the LNAPL-gas exposure conditions and the distribution of LNAPL, shows a "decreasing-then increasing" pattern in both models. The three-phase equilibrium state is disrupted by groundwater fluctuation, which is manifested by the enhanced volatilization during the stage of groundwater elevation, when the average volatile flux in the two models is 124%～126% higher compared to the steady scenario.This research provides a theoretical basis for the understanding of LNAPL pollution process in heterogeneous contaminated sites.
- LNAPL /
- vadose zone /
- heterogeneity /
- numerical model

HTML全文

图 1 概念模型示意图

Figure 1.

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图 2 各透镜体模型中的含水率变化规律

Figure 2.

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图 3 细砂透镜体中不同时刻LNAPL饱和度分布

Figure 3.

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图 4 粗砂透镜体中不同时刻LNAPL饱和度分布

Figure 4.

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图 5 细砂透镜体周围各观察点S_NAPL对比（0～360 min）

Figure 5.

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图 6 地下水位波动情景中不同时刻LNAPL饱和度分布

Figure 6.

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图 7 水位恒定与波动条件下细砂透镜体附近S_NAPL对比

Figure 7.

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图 8 水位恒定与波动条件下粗砂透镜体附近S_NAPL对比

Figure 8.

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图 9 细砂、粗砂透镜体中不同时刻LNAPL在水相中的质量分数x(aq)

Figure 9.

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图 10 不同透镜体模型中LNAPL挥发通量对比

Figure 10.

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图 11 不同水位情景中LNAPL挥发通量对比

Figure 11.

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表 1 介质相关参数^[17,25-26]

Table 1. Medium-relevant parameters

介质类型		中砂	细砂	粗砂
孔隙度		0.35	0.40	0.30
饱和渗透率/(m²)		2.37×10⁻¹¹	1.48×10⁻¹²	2.26×10⁻¹⁰
颗粒比重/(kg∙m⁻³)		1650.00	1510.00	1749.00
相对渗透率 Stone模型	S_wr	0.05	0.15	0.03
	S_nr	0.04	0.08	0.03
	S_gr	0.00	0.00	0.00
	n	2.93	3.00	3.00
毛细压力 van- Genuchten模型	m	0.66	0.67	0.67
	S_lr	0.02	0.12	0.02
	P₀⁻¹	5.105×10⁻⁴	3.75×10⁻⁴	6.02×10⁻⁴
	P_max	5×10⁵	1×10⁷	5×10⁵
	S_ls	1.00	1.00	1.00

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表 2 甲苯相关参数^[24]

Table 2. Toluene-relevant parameters

参数	气相中扩散系数/(m²∙s⁻¹)	水相中扩散系数/(m²∙s⁻¹)	NAPL相扩散系数/(m²∙s⁻¹)	水中溶解度/(mol∙mol⁻¹)
数值	8.8×10⁻⁶	6.0×10⁻¹⁰	6.0×10⁻¹⁰	1.01×10⁻⁴

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