Analytical model for transient coupled consolidation and contaminant transport in landfill liner system

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A composite liner system consisting of a geomembrane layer (GMBL), a compacted clay layer (CCL) and an attenuation layer (AL) is widely used in the modern landfills. The field and experimental observations highlight the potential detrimental effects on breakthrough of contaminants induced by consolidation of soil liner when a relatively high applied stress is caused by the waste placement. A one dimensional steady‐state model is developed to investigate the behaviour of contaminant transport in GMBL/CCL/AL composite liner system considering consolidation. Effects of the consolidation process on the transport of typical contaminants are investigated by the proposed analytical solution. The analytical results show that the magnitude of volume compressibility coefficient in the AL is important in controlling the overall magnitude of the consolidation induced effects. The process of consolidation shows a larger impact on the absorbable pollutants compared to the non‐absorbable pollutants. This may be due to the fact that the migration of solid particles induced by the consolidation may assist the transport of contaminant absorbed on them. The thickness of the AL shows large impacts on the bottom flux for the case with a high volume compressible coefficient. Increasing the thickness of AL from 1 to 3 m can results in a factor of 2.6 increase of the bottom flux. Increasing the thickness of the AL leads to a larger consolidation advection and a longer consolidation path, which may be the dominant mechanisms for contaminant transport compared to the diffusion process.

Section: Analytical Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Analytical solution for one‐dimensional steady‐state contaminant transport through a geomembrane layer (GMBL)/compacted clay layer (CCL)/attenuation layer (AL) composite liner considering consolidation

Yan

Xie

Ding

et al. 2022

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An analytical model for contaminant transport in landfill liner with fluctuating leachate head

Xie

Thomas

et al. 2022

Leachate head in municipal solid waste (MSW) landfills can be very high (e.g., >10 m) in some Chinese landfills and can continuously change during the service life of the landfill. Variations of leachate head can induce time-dependent seepage velocity changes in the liner, which may lead to a change of transport mechanisms of contaminants. An analytical model for contaminant transport through clay liner system considering the effects of leachate head variations is presented. The analytical solution is obtained using the recursive method and the Green's function approach. The proposed analytical solution is verified by numerical results. The model is then applied to investigate the effects of variable leachate head on the transport of contaminants. The results indicated that timedependent advection arising from leachate head variations may play a significant part when investigating contaminant transport through a clay liner. The contaminant concentrations at the bottom of the liner predicted by using fixed leachate head may be underestimated compared to the case with variable leachate heads. The bottom concentration of Pb 2+ at t = 50 years for the case with H D = 60 m can be 6.6 times larger than that of the case with fixed leachate head. The mechanisms of contaminant transfer may change from a diffusion-dominated process to an advection-dominated process. For example, the molecular diffusion is the dominant process in Event 1 (e.g., t < 5 years with Peclet number < 1) while advection induced by the variations of leachate head may play a more important role for contaminant transport when t > 5 years. Increasing leachate head can result in an earlier breakthrough time and steady state for contaminant transport. The breakthrough time of DCM for the case with H D = 60 m can be 1.6 times lower than that for the case with fixed leachate head. Considering the effects of leachate head variations may be critical to design a more stable and reliable landfill liner.

Analytical solutions for chemical dissolution‐front instability problems involving radially divergent flow within fluid‐saturated porous media

Zhao

Hobbs

Ord

2023

Through using rigorously mathematical deductions, this article derives analytical solutions for chemical dissolution‐front instability (CDFI) problems, in which radially divergent flow is involved within fluid‐saturated porous media. Since the acid injection‐well to be considered is a circle of nonzero radius in the horizontal plane, a polar coordinate system is used to describe the coupled mathematical governing equations of the CDFI problem. To facilitate deriving analytical solutions, an appropriate mathematical transform is used to convert the coupled mathematical governing equations from a dimensional form into a dimensionless one. This enables the generalized linear stability approach to be utilized for deriving both analytical base and perturbation solutions for the CDFI problem involving radially divergent flow within a fluid‐saturated porous medium. Consequently, a theoretical criterion, which is usable for assessing the CDFI in the chemical dissolution system (CDS), is further established from the corresponding analytical perturbation solutions. The related theoretical results have demonstrated that: (1) the proposed theoretical criterion is useful and applicable for assessing the CDFI associated with radially divergent flow within fluid‐saturated porous media; (2) the permeability ratio between the downstream and upstream regions can affect significantly the critical Peclet number of a CDS associated with radially divergent flow; (3) the initial porosity can have remarkable effects on the critical Peclet number of a CDS associated with radially divergent flow; and (4) the difference between the final and initial porosities can also affect significantly the critical Peclet number of a CDS associated with radially divergent flow in the fluid‐saturated porous medium.