Impact of permeable conduits on solute transport in aquitards: Mathematical models and their application
Bibliographic record
Abstract
The migration of contaminants through porous conduits (for example, sand layers) in aquitards, or any preferential flow feature within a low‐permeability matrix, can be significantly retarded via diffusion into the matrix and processes such as sorption and decay. Previous solutions for simulating contaminant transport in these types of environments have been limited to a parallel‐plate approach such as that used in studies of fractured rock aquifers. A major drawback of using these approaches is that they cannot account for the radial component of diffusion that occurs from circular‐ or elliptical‐sectioned conduits. We have developed solutions for both of the latter cases and compared results from generic simulations to those obtained with a conventional parallel‐plate model. The results demonstrated using a circular conduit approach can produce concentration profiles for both the conduit and surrounding matrix that are up to several orders of magnitude lower than those predicted using parallel‐plate models. The solutions for elliptical‐section conduits provide concentration profiles that are bounded by the circular‐ and parallel‐plate models. We also present several generic simulations to demonstrate the effects of conduit radius and average groundwater flow velocity on concentration profiles. Finally, the circular conduit model is applied to a clay‐rich till aquitard in southern Saskatchewan, Canada to provide insight into an anomalous dissolved chloride peak in the vertical pore water profile. The model demonstrates that the source of the high Cl− could be as far as 10–100 km from the site (although this distance may be unrealistic) and allows estimation of the Cl− concentration at the source. We envisage that the solutions for conduit diffusion will have far wider applications than just aquitard studies, and future uses may include tracer tests in karstic and fractured aquifers.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".