Inferring high-resolution aquifer hydraulic conductivity and groundwater fluxes by active heat tracer using direct push fiber optics
Bibliographic record
Abstract
Characterizing aquifer heterogeneity for contaminant transport prediction remains a challenge in subsurface hydrology. In recent years, fiber optics (FO) Distributed Temperature Sensing (DTS) has enabled the study of transient hydrogeological processes with high spatial and temporal resolutions. Recent studies have shown that vertical profiles of groundwater fluxes can be quantified in granular aquifers through inversion of the thermal responses from active heat tracer tests using FO cables installed by direct push. Here, we further investigate the potential of active FO-DTS methods for granular aquifer characterization by performing a multiscale characterization and active heat tracer experiment in a well-characterized heterogeneous deltaic aquifer located north of Quebec City, Canada. This aquifer has been the object of detailed hydrogeological characterization and thus provides a wide range of existing data. In particular, we will test whether the vertical distribution of groundwater fluxes in the sub-surface determined by these inversions can be used to estimate hydraulic properties at a spatial scale that can be used to assess the impact of aquifer heterogeneity on mass transport and dispersion. This communication focuses on a site where two FO cables were installed 10 m apart by direct push. An active heat tracer experiment was carried out with the two FO cables, and the resulting thermal responses were inverted to obtain high-resolution vertical profiles of the groundwater fluxes at each FO cable. Heating was carried out in the saturated zone, between depths of 12 to 40 m with a 25-cm vertical sampling. Using data from a piezometric survey, the groundwater fluxes from the FO-DTS were used to estimate a range of hydraulic conductivities (K). A previous study at the field site has shown that cone penetration test (CPT) profiles can be used to recognize the different hydrofacies with distinct ranges of hydraulic conductivity present in the deltaic aquifer. As the two FO cables were co-located with a previously done CPT profile, the measured fluxes and estimated K values could be compared to known ranges of K. Results show quite varying temperature profiles and accordingly distinct groundwater fluxes. These varying fluxes are coherently correlated to the different hydrofacies identified with the co-located CPT responses at a similar vertical scale. The two FO-DTS temperature profiles are also quite similar when considering the small variations in hydrofacies found along their length. These results show that FO-DTS heat tracer tests provide consistent and representative measurements of groundwater fluxes in agreement with the heterogeneous distribution of K as indicated by CPT. Thus, compared with existing hydraulic methods, FO-DTS heat tracer tests provide new and complementary data that have a great potential for characterizing solute transport in granular aquifers with a high spatial resolution.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".