Exercise 5 – Impact of Rock Mass Depressurization on Regional Flow
The cartoon below illustrates a proposed depressurization system for an open pit mine located in a limestone formation in mountainous terrain. A local community in the nearby valley relies on springs that discharge within the community property boundary for their potable water. Assume there are no dominant structural or dissolution features in the limestone that could control the pattern and rate of groundwater flow.
Figure Exercise 5–1 – Proposed depressurization system for open pit mine.
- Derive a first-order estimate of the time it takes to observe a reduction in the hydraulic head in the vicinity of the springs due to the operation of the depressurization wells.
- Assuming solute transport occurs only by advection, estimate the travel time of a solute that is mobilized by sulfide mineral oxidation on the pit walls, bypasses the capture zone of the production wells, and migrates to a discharge point at the springs.
The distance from the pumping wells to the springs is 3000 m. The distance from the open pit to the springs is 2800 m. Assume the effective hydraulic conductivity of the limestone is 5×10–6 m/s, the specific storage is 1×10–4 m–1, and its effective porosity is 0.05. Assume the elevation difference between the floor of the pit and the springs is 200 m.
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