Response to Pumping in a Two-Aquifer System

Xiaomin Wang, Christopher J. Neville

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: General Hydrogeology I

ABSTRACT: Classical methods of pumping test interpretation do not address situations in which pumping is from a basal unconsolidated aquifer underlain by weathered rock. To guide the interpretation, Cooper-Jacob analyses are applied to the results from a three-dimensional numerical model. Three cases with different properties are investigated with two outer boundary conditions for the model. The results show that the inferred apparent transmissivity corresponds to the cumulative transmissivity. For the case of a zero-drawdown boundary, all of the pumped water is supplied eventually by the boundary and drawdowns stabilize. When the pumped aquifer is underlain by a more transmissive aquifer the drawdowns stabilize more rapidly and at smaller levels. For the case of a no-flow boundary, the drawdowns are more complex and eventually increase without bound. In the case where the unit underlying the pumped aquifer is more transmissive the propagation of drawdowns to the no-flow boundary is hastened.

RÉSUMÉ: Les méthodes classiques d'interprétation des tests de pompage ne traitent pas des situations dans lesquelles le pompage Cooper Jacob est appliquée aux résultats d'un modèle numérique tridimensionnel. Trois cas avec différentes propriétés sont étudiés avec deux types de conditions limites externes pour le modèle. Les résultats montrent que la transmissivité apparente calculée correspond à la transmissivité cumulative. Pour le cas avec condition limite de rabattement nul, toute l'eau pompée est ultimement fournie par la condition limite et les rabattements se stabilisent. Lorsque l'aquifère pompé est sous-tendu par un aquifère plus transmissif, les rabattements se stabilisent plus rapidement et sont moins importants. Pour le cas d'une condition limite imperméable, les rabattements sont plus complexes et augmentent continuellement. Dans le cas où la couche sous l'aquifère pompé est plus transmissive, la propagation des rabattements vers la limite imperméable est accélérée.

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