Field study of hydrogeologic characterization methods in a heterogeneous aquifer

Area of Science:

• Hydrogeology
• Environmental Engineering
• Geosciences

Background:

• Accurate transient groundwater flow models depend on precise hydraulic conductivity (K) and specific storage (S(s)) parameters.
• Highly heterogeneous geological deposits present significant challenges in characterizing these hydraulic properties.
• Understanding spatial variability is crucial for reliable groundwater resource management and contaminant transport modeling.

Purpose of the Study:

• To evaluate the effectiveness of common hydrogeologic characterization approaches in defining hydraulic property distributions within a heterogeneous glaciofluvial deposit.
• To compare the predictive accuracy of different characterization methods using drawdown responses from pumping tests.
• To assess the impact of model complexity on the prediction of transient groundwater flow.

Main Methods:

• Field instrumentation included four 18-m deep Continuous Multichannel Tubing (CMT) wells and a central multiscreen pumping well within a 15m x 15m area.
• Core samples were analyzed using the Unified Soil Classification System, grain size analysis, and permeameter tests to estimate K.
• Slug tests and pumping tests were conducted to obtain both small-scale and larger-scale estimates of K and S(s).
• A 3D numerical model (HydroGeoSphere) was used to simulate transient drawdown data and evaluate the various K and S(s) estimates.

Main Results:

• Geostatistical analysis of small-scale data revealed strongly heterogeneous three-dimensional K fields.
• Permeameter and empirical relationships provided 471 and 270 K estimates, respectively.
• Slug tests yielded additional K estimates from 28 ports.
• Numerical simulations indicated that increased model complexity generally improved drawdown predictions.
• However, the accuracy of drawdown predictions across all CMT ports remained inconsistent.

Conclusions:

• Characterizing highly heterogeneous deposits requires a multi-method approach combining small-scale and large-scale hydraulic property estimations.
• While advanced modeling improves predictive capabilities, achieving consistent accuracy in transient groundwater flow simulations across all monitoring locations is challenging.
• Further research is needed to refine hydrogeologic characterization techniques for complex subsurface environments.