Layered Radial Aquifer Model for Open-Pit Mine Closure with Managed Aquifer Recharge.

Area of Science:

• Hydrogeology
• Environmental Engineering
• Water Resource Management

Background:

• Open-pit mine dewatering impedes post-closure pit lake recovery.
• Managed aquifer recharge (MAR) is a key strategy for mitigating dewatering impacts.
• Existing models often simplify aquifer systems, limiting application to layered hydrogeology.

Purpose of the Study:

• To develop and apply a coupled two-aquifer model for simulating MAR in layered post-mining environments.
• To evaluate the effectiveness of different MAR strategies (unconfined vs. split injection) on pit lake recovery times.
• To provide guidance for optimizing MAR design in layered hydrogeologic settings.

Main Methods:

• Development of a radially symmetric, two-aquifer model incorporating an unconfined aquifer, leaky aquitard, and confined aquifer.
• Coupling the aquifer model with a pit water-balance equation to simulate pit lake recovery dynamics.
• Nondimensionalization to create transferable type curves and a design workflow based on key hydrogeologic parameters.
• Evaluation of 15 hydrogeologic scenarios under three MAR allocations: no MAR, 80% unconfined injection (MARu80), and split injection (MARsplit).

Main Results:

• MAR significantly reduces pit lake recovery time; MARu80 decreased recovery time by a median factor of 0.17 compared to no MAR.
• Split injection (MARsplit) can further shorten recovery in moderately to highly coupled layered systems but may increase mounding and recycling.
• Layered aquifer systems show 2-3 times faster recovery than homogeneous systems under the same MAR policy, highlighting the importance of hydrogeologic structure.

Conclusions:

• MAR is an effective strategy for accelerating post-mining pit lake recovery in layered hydrogeologic settings.
• Confined aquifer injection can enhance recovery but requires careful consideration of potential mounding and recycling effects.
• The developed model and type curves offer valuable screening tools for designing MAR systems to optimize pit lake restoration.