Contaminant migration through the permafrost active layer, Mackenzie Delta area, Northwest Territories, Canada
Bibliographic record
Abstract
Abstract Buried pits (sumps), used for the disposal of drilling muds in the Mackenzie Delta area of Arctic Canada, provide an opportunity for assessing the effectiveness of ice-bonded permafrost sediments as a containment for industrial wastes. Potassium chloride (KCI) added to drilling muds as a freezing-point depressant provides a suitable tracer, because it is easily identified and natural concentrations in sediment pore water are typically low (less than 0.02 g l−1; potassium). Muds with KCI concentrations of up to 10% by weight (100 g l−1) have been used. In the vicinity of sumps, potassium is found at elevated concentrations of up to several g l−1 in the seasonal thaw layer (active layer) at distances well beyond what would be expected from diffusive transport alone. Within the level alluvial silts of the modern Mackenzie Delta, KCI has moved up to 50 m laterally from sump edges. On surrounding tundra uplands, KCI has migrated several hundred metres downslope within the active layer. Although ice-rich permafrost sediments appear to form an effective barrier against downward movement of solutes, thawing ice lenses and veins within the active layer greatly increase the lateral hydraulic conductivity in this zone during the thaw season. Compared with unfrozen silty sediments, the large pores left by thawed ice fabric in the same sediment after a freeze–thaw cycle have been shown to increase the hydraulic conductivity up to four orders of magnitude. This phenomenon is probably common in thawing, ice-rich sediments and presumably favours accelerated downhill movement of solutes. On level ground, it is anticipated that KCI movement is promoted by fluid densities approaching that of sea water. Laboratory experiments with thawed sand and both unfrozen and thawing Mackenzie Delta silt confirm the existence of density-driven solute movement and the importance of thawing ice fabric in promoting solute movement. The thawed ice fabric of active-layer sediments and the presence of a frost table promote lateral movement of fluids when a density or elevation gradient is present. These tendencies widen the area potentially affected by contaminant migration from abandoned waste sites and they may also promote the movement of contaminants that escape from future containments.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 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".