Exercise 1 – Solute Loading
The shaded zone in the Figure Exercise 1-1 below identifies the location of a small waste rock stockpile on an upland slope, some 200 m away from a stream channel in the valley floor. The stockpile is releasing sulphate to an underlying unconfined aquifer. The depth to the water table at the topographic divide is 10 m. The contours present the vertically averaged sulphate concentration across the saturated thickness of the aquifer. Given the data provided below: (1) Estimate the mass of sulphate entering the stream channel each day that originates from the waste rock stockpile; and (2) List the key assumptions you have made to develop this loading estimate.
For ease of calculation, assume the aquifer is composed of a homogeneous sand with a hydraulic conductivity of 5×10–4 m/s. Assume the aquifer averages 10 m in thickness. Assume the highest sulphate concentration observed at any depth in the monitoring well indicated by the star is 310 mg/L. For ease of calculation, assume a background sulphate concentration in the aquifer less than 5 mg/L.
Figure Exercise 1–1 – Schematic of Exercise 1.