Simulating regional groundwater flow in layered, faulted sedimentary basins: implications for groundwater age and shale gas
Bibliographic record
Abstract
Groundwater plays an important role in a wide range of geologic processes. Sedimentary basins are heterogeneous, layered and faulted which strongly impacts regional groundwater flow. An important concern is how anthropogenic alterations such as groundwater or shale gas development affect these complex systems. Heterogeneities are likely to impact groundwater age and affect geologic processes that depend on groundwater or solute fluxes. They may also enhance long term contamination of shallow aquifers from the fracturing of the target shale unit, as contaminants may migrate from the shale to shallow aquifers through preferential pathways such as faults. We use numerical modelling to study the effect of a layered system on distribution of groundwater age in a regional groundwater basin and the impact of hydraulic fracturing in a generic faulted sedimentary basin on potential contamination of a shallow aquifer. First, we show that high age zones with predictable locations occur in layered geologic systems across a wide range of hydraulic gradients, basin geometries and permeabilities. The zones of older groundwater result from two mechanisms: low groundwater velocities in the low permeability layer; and the rejuvenation of the groundwater through mixing of different flow paths near discharge zones. Second, we show that hydraulic fracturing leads to the transport of contaminants along the fault and long-term contamination of a shallow aquifer in some specific, realistic cases. The location of the hydro-fractured zone relative to the fault zone and the top of the shale is the most critical factor controlling contaminant transport potential.
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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 | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| 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".