Effect of uncertain hydraulic conductivity on the fate and transport of BTEX compounds at a \nfield site
Bibliographic record
Abstract
A Monte Carlo analysis was conducted to investigate the effect of uncertain hydraulic conductivity on the fate and transport of BTEX compounds (benzene, toluene, ethyl benzene, and xylene) at a field site on Hill Air Force Base, Utah.Microbially mediated BTEX degradation has occurred at the site through multiple terminal electron-accepting processes, including aerobic respiration, denitrification, Fe(III) reduction, sulfate reduction, and methanogenesis degradation.Multiple realizations of the hydraulic conductivity field were generated and substituted into a multispecies reactive transport model developed and calibrated for the Hill AFB site in a previous study.Simulation results show that the calculated total BTEX masses (released from a constant-concentration source) that remain in the aquifer at the end of the simulation period statistically follow a lognormal distribution.In the first analysis (base case), the calculated total BTEX mass varies from a minimum of 12% less and a maximum of 60% more than that of the previously calibrated model.This suggests that the uncertainty in hydraulic conductivity can lead to significant uncertainties in modeling the fate and transport of BTEX.Geometric analyses of calculated plume configurations show that a higher BTEX mass is associated with wider lateral spreading, while a lower mass is associated with longer longitudinal extension.More BTEX mass in the aquifer causes either a large depletion of dissolved oxygen (DO) and NO 3 -, or a large depletion of DO and a large production of Fe 2+ , with moderately depleted NO 3 -.In an additional analysis, the effect of varying degrees of aquifer heterogeneity and associated uncertainty is examined by considering hydraulic conductivity with different variances and correlation lengths.An increase in variance leads to a higher average BTEX mass in the aquifer, while an increase in correlation length results in a lower average.This observation is explained by relevant partitioning of BTEX into the aquifer from the LNAPL source.Although these findings may only be applicable to the field conditions considered in this study, the methodology used and insights gained are of general interest and relevance to other fuel-hydrocarbon naturalattenuation sites.
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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 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| 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".