A Type-Curve Method for the Analysis of Pumping Tests with Piecewise-Linear Pumping Rates.

Area of Science:

• Hydrogeology
• Geotechnical Engineering
• Environmental Science

Background:

• Constant-rate pumping tests are standard for aquifer analysis, but variable rates are common in practice.
• Existing methods struggle to accurately analyze aquifer hydraulic parameters under variable pumping conditions.
• Confined aquifers require specialized analytical solutions for accurate parameter estimation.

Purpose of the Study:

• To develop a generally applicable dimensionless analytical solution for variable-rate pumping tests in confined aquifers.
• To propose a novel type-curve method for estimating hydraulic conductivity (K) and specific storage (Ss).
• To validate the method's applicability and robustness using synthetic and field data.

Main Methods:

• Adopting a piecewise-linear fitting approach for variable pumping rates.
• Developing a type-curve matching technique using log-log plots of observed drawdown data.
• Utilizing dimensionless parameters including the first dimensionless inflection time.
• Comparing results with established methods like PEST for validation.

Main Results:

• The proposed type-curve method accurately estimates hydraulic conductivity (K) and specific storage (Ss) from variable-rate pumping tests.
• Parameter estimates closely align with those obtained using the PEST software.
• The study revealed spatial heterogeneity in K and Ss values between different observation wells.
• The method demonstrated robustness in analyzing drawdown data from a multilayered aquifer system.

Conclusions:

• The new type-curve method provides a reliable approach for analyzing variable-rate pumping tests in confined aquifers.
• The findings highlight the importance of considering spatial heterogeneity in aquifer hydraulic parameters.
• Further research can explore characterizing K and Ss heterogeneity using variable-rate pumping test data.