Investigating gas phase processes in natural and hydrocarbon-contaminated groundwater
Notice bibliographique
Résumé
Here the nature of gas phase processes and their implications for flow and transport were examined using a pilot-scale, 2-dimensional, laboratory tank instrumented for direct, in situ trapped gas measurements. Experimental conditions mimicked an unconfined, homogeneous sand aquifer with horizontal flow. Key areas of investigation included i) trapped gas dissolution following a water table fluctuation; and ii) gas phase dynamics within a hydrocarbon plume experiencing dissolved gas production via biodegradation. In the first experiment, dissolution occurred as a diffuse, wedge-shaped front propagating down-gradient in the tank over time, with enhanced dissolution at depth. Front advancement at the deepest monitoring point was 4.1 - 5.7x faster. This dynamic, depth-dependent pattern was mainly attributed to increased dissolved gas solubility. An estimated 12% increase in quasi-saturated hydraulic conductivity (Kqs) also contributed to greater dissolution at depth. Overall, the dissolution front near the water table advanced 1 m down-gradient in 344 days, suggesting that gas trapped shallowly will likely persist for significant periods of time. The utility of total dissolved gas pressure sensors for simple in-well measurements to detect trapped gas and monitor its dissolution were also demonstrated. During the second experiment, biodegradation occurred under variable redox conditions, ranging from denitrification to methanogenesis. Significant in situ increases in trapped gas were observed within the tank over 330 days. Maximum gas saturations never exceeded 27% of pore volume even during continued dissolved gas production, indicating ebullition upon reaching a gas phase mobilization threshold. Consequently, associated reductions in Kqs were restricted to a factor of 2 or less, but still appeared to alter the groundwater flow field. While trapped gas increases within the biodegradation plume were expected, declines in gas saturations were also observed. Thus, the overall pattern of trapped gas growth exhibited high spatial and temporal variability. Influencing factors included changes in hydrocarbon inputs and microbial controls on redox zonation, in addition to ebullition and changes in groundwater flow; emphasizing that gas phase growth in contaminant plumes will be highly complex and dynamic in the natural systems. Given the impacts on hydraulic conductivity, and the fate and transport of volatile compounds, an improved understanding of quasi-saturated conditions will be beneficial for various groundwater applications, from recharge and paleoclimate studies to site characterizations and remediation strategies.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».