Two borings spaced 50m apart were drilled at a project site. The borings show a

Question

Two borings spaced 50m apart were drilled at a project site. The borings show a soil profile of approximately 5m of nearly impervious clay, underlain by 6m of clean uniform sand, 4m of silty sand, and 10 m of clean, well-graded sand, underlain by nearly impervious clay. The ground elevation of B-1 is EL 900m and B-2 is EL 895 m. The drillers logs indicated groundwater was encountered at the top of the sand layers in both borings. Piezometers installed near B-1 and B-2 indicate a piezometric head of 915 m (measured at EL 885m) near B-1 and 885 m near B-2 (measured at EL835m).

A) The ground water encounter at this site would most likely be classify as what kind of aquifer?

B) If a well were installed anywhere between boring B-1 and B-1, would a pump need to be installed for water to flow from it (assmume top of the well is within 1.5m of the ground surface).

Please show how to get the answer so I can work it through and understand it. Thank you!

Explanation / Answer

a.) Considering the type of readings shown by Piezometers & considering the geolgical formations, it seems to be a Confined Acquifer.

b.) Yes a pump would be required to pump the water upwards because the acquifer being comfined in nature. The piezometer readings at B2 show that the original water table could be lower than as depicted in borelogs. Hence, although the intially the water may flow as the unsaturated or partically saturated zone above water table will flow through the well, but with passage of time the water will reach the water table i.e. the saturated zone & hence the upward pressure will not be sufficient for water to flow as the head would not be much.

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