Modeling variably saturated subsurface solute transport with MODFLOW-UZF and MT3DMS.

Area of Science:

• Environmental Modeling
• Hydrogeology
• Geochemistry

Background:

• Groundwater solute transport is often simulated using MT3DMS.
• Simulating unsaturated zone flow and transport presents unique challenges.
• Existing models may require significant computational resources.

Purpose of the Study:

• To modify the MT3DMS model for unsaturated zone solute transport simulation.
• To integrate the UZF1 package from MODFLOW into MT3DMS.
• To develop an efficient and accurate tool for variably saturated flow and transport.

Main Methods:

• Incorporated the UZF1 package into MT3DMS code.
• Employed a volume-averaged approach mapping UZF1 fluxes to a fixed grid.
• Validated the UZF-MT3DMS model against analytical benchmarks and existing codes.

Main Results:

• UZF-MT3DMS accurately simulates solute advection, dispersion, and reaction in unsaturated zones.
• The model correctly simulates unsaturated-saturated zone interactions.
• Significant runtime savings were achieved, with 3D simulations running up to ten times faster.

Conclusions:

• UZF-MT3DMS provides an accurate and efficient solution for unsaturated zone solute transport.
• The analytical nature of the UZF1 solution reduces computational and data burdens.
• This enhanced modeling framework benefits a wide user base familiar with MODFLOW and MT3DMS.