Repeat Problem if the clean sand unit extends below the landfill to an elevation of 25 ft...

Repeat Problem if the clean sand unit extends below the landfill to an elevation of 25 ft msl. The clay liner exists around and on the bottom of the landfill. Consider Darcy’s law across both the sides and bottom of the clay liner.

Problem

A landfill liner is laid at elevation 50 ft msl (mean sea level) on top of a good clay unit. A clean sand unit extends from elevation 50 ft to elevation 75 ft, and another clay unit extends up to the surface, located at elevation 100 ft. The landfill can be represented by a square with length of 500 ft on a side and a vertical depth of 50 ft from the surface. The landfill has a 3-ft-thick clay liner with K = 10-7 cm/s around the sides and bottom, as shown in Figure. The regional ground water level for the confined sand (K = 10–2 cm/s) is located at a depth of 10 ft below the surface, or elevation = 90 ft.

How much water will have to be continuously pumped from the landfill to keep the potentiometric surface at 60 ft elevation (msl) within the landfill? Assume mostly horizontal flow through the clay liner.

Figure