For construction of a tubewell, the following formations were obtained from drilling: an unconfined aquifer between 12 m and 16 m and a confined aquifer between 30 m and 40 m below ground level. A horizontal centrifugal pump installed on the ground level can pump water from the constructed tubewell. Probable static water level from the ground surface in m is
Options:
(A) 5
(B) 12
(C) 16
(D) 30
Official Answer Key:
B
Step-by-Step Solution & Explanation
A horizontal centrifugal pump is a surface (suction-lift) pump; it can only operate if the static water level lies within its practical suction-lift limit (roughly 6–7 m in the field). Of the two aquifers tapped, the shallow unconfined aquifer's water table is the one that governs the static water level at the ground surface — and for an unconfined aquifer the phreatic (static) water surface lies essentially at the top of the saturated formation, i.e., at the top of the unconfined layer identified during drilling, at 12 m depth. This is consistent with using a horizontal centrifugal (surface) pump only if the effective lift is manageable, and among the given options 12 m (top of the unconfined aquifer) is the physically consistent 'probable' static water level, matching option (B).
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