As shown in the figure below $($Fig$\mathrm{.}4),$ a risk of ground water contamination by the leakage of

pollutant from a buried drum in a clay layer is found. To prevent the expansion of the pollution in

the aquifer underlying the clay, a single well shall be urgently installed for pumping the water from

the aquifer. Indicate the appropriate location of the well in the figures of the last answer sheet and

explain the reason of the well location. $(15)$

Cross section

Plan

Fig. $4$