Experimental Study on the Lateral Seepage Characteristics in the Tension Saturated Zone.

Yongfeng Gong,Minghong Li,Xu Guo,Zuo Liu,Chuanming Ma

doi:10.3390/ijerph18105098

Yongfeng Gong, Minghong Li + Show 3 more

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https://doi.org/10.3390/ijerph18105098

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Abstract

To study the lateral seepage field in the tension saturated zone (TSZ), an experiment with no evaporation and precipitation infiltration was carried out in a self-made seepage tank filled up with fine sand. Based on the data and plots obtained, the lateral seepage field distribution features in the TSZ can be divided into three area for discussion: ascending area, descending area, and the nearly horizontal flow area. In the ascending and descending area, the total water potential gradient diminished from the recharge area to the discharge area and the seepage velocity was faster. In the nearly horizontal flow area, the total water potential gradient was lower and the seepage velocity was slower. The pressure potential gradually decreased horizontally from the recharge area to the discharge area, while in the vertical profile, it gradually decreased from the bottom to the top in the whole seepage area. In the absence of evaporation, the vertical water exchange among the saturated zone, TSZ, and unsaturated zone in nearly horizontal flow area is weak. Contrarily, in the ascending area and descending area, vertical water flows through both the phreatic surface and the upper interface of the TSZ. When there is lateral seepage in the TSZ, the thickness of the TSZ generally increases from the ascending area to the nearly horizontal area and then to the descending area. It should be pointed out that in the nearly horizontal area, the TSZ thickness is approximately equal to the height of the water column. Overall, the lateral seepage in the TSZ can be regarded as a stable siphon process, hence the siphon tube model can be further used to depict this lateral seepage.

Highlights

Lateral flow research in the unsaturated zone began in the middle of the last century [1].lateral seepage in the tension saturated zone (TSZ) is often underestimated due to the fact that the TSZ is relatively thinner than the saturated zone [2]
Field experiments involving pollutant tracers support the importance of lateral seepage of the TSZ; Freitas and Barker (2011) confirmed the fuel mixtures released into the unsaturated zone accumulated in the TSZ as they are lighter than water [8]
The flow field in the TSZ could be divided into three parts (Figure 4): (1) Around the recharge area, where the water flow was mainly upward

Summary

Introduction

Lateral flow research in the unsaturated zone began in the middle of the last century [1]. Lateral seepage in the tension saturated zone (TSZ) is often underestimated due to the fact that the TSZ is relatively thinner than the saturated zone [2]. The TSZ has been proved to be the crucial way for contaminants from the surface to enter into groundwater, and the lateral flow of the TSZ plays an important role in transporting contaminants in an aquifer system [4,5,6,7]. Field experiments involving pollutant tracers support the importance of lateral seepage of the TSZ; Freitas and Barker (2011) confirmed the fuel mixtures released into the unsaturated zone (at the CFB Borden aquifer) accumulated in the TSZ as they are lighter than water [8]. In field experiments of Abit et al (2008), the movement of both NO3 − and

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