Flow to a well in a five-layer system with application to the Oxnard Basin.

Area of Science:

• Hydrogeology
• Groundwater Modeling
• Analytical Solutions

Background:

• Neuman (1968) developed an analytical solution for three-aquifer systems, but the five-layer solution remained unevaluated.
• Previous studies highlighted the importance of considering drawdowns in unpumped aquifers in leaky aquifer theories.

Purpose of the Study:

• To numerically evaluate Neuman's five-layer analytical solution for groundwater drawdown.
• To reinterpret a large-scale pumping test near Oxnard, California, using this solution and parameter estimation.

Main Methods:

• Numerical inversion of the Laplace-transformed five-layer analytical solution.
• Coupling the analytical solution with the PEST parameter estimation code.
• Validation against drawdowns from a subsequent pumping test at the Oxnard site.

Main Results:

• The five-layer solution demonstrates that pumping effects propagate across all layers.
• Reinterpretation of the Oxnard pumping test yielded parameter estimates comparable to previous studies.
• The coupled model successfully validated against observed drawdowns.

Conclusions:

• The evaluated five-layer analytical solution is effective for analyzing complex, multi-aquifer systems.
• This approach provides a robust method for hydrogeological parameter estimation.
• The findings reinforce the significance of accounting for interconnected aquifer responses in groundwater modeling.