Age distribution of groundwater in fractured aquifers of the St. Lawrence Lowlands (Canada) determined by environmental tracers (3H/3He, 85Kr, SF6, CFC-12, 14C)
Bibliographic record
Abstract
Information about the age distribution of groundwater provides unique and particularly relevant insights about groundwater flow and mixing conditions, as well as about the vulnerability and sustainability of the resource. Constraining flow paths in heterogeneous and fractured aquifers requires spatially distributed and depth-related observations. Where multiple wellbores are not available, depth-specific samples from individual long open-borehole wells may provide useful information. In this study, results from depth-specific sampling of environmental tracers (3H, 85Kr, SF6, CFC-12, noble gases, 13C, 14C) are reported from seven long open-borehole wells (depths ≤100 m below the surface) in the area of the St Lawrence Lowlands (Quebec, Canada). The multitracing approach allowed for the determination of the groundwater mixing conditions within the fractured-rock aquifers. The results indicate that fracture networks induce complex groundwater mixing patterns, without any evidence that the residence times significantly increase with the depth. Under unstressed conditions, the investigated aquifers contain 20–50% “modern” water (less than 60 years old) and 50–80% “old” water with residence times of ~4–11,000 years. The observed groundwater bi-modal age distribution is caused by fast flows through interconnected fractures and slow flows through poorly connected fractures or the primary porosity of the rock. Within the catchment of the wellfields, the pumped groundwater becomes essentially “modern” because of the preferential draining of productive fractures, while the water within the less transmissive volumes cannot be leaked out as fast. Thus, groundwater abstraction increases the aquifer’s intrinsic vulnerability to anthropogenic pollution.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 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 teacher head, 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".