a) Describe the concepts of groundwater and aquifer. (4 marks) b) Explain the formation of freshwater lenses on Pacific islands, with the help of a drawing containing the variation of the fresh water level above and below the sea-level. (8 marks) c) Explain what happens with the water level in the aquifer around pumped wells. (5 marks) d) A pollutant is released into an aquifer and it is spreading towards a drinking well. Describe how a system of wells can be used to prevent the spread of the pollutant towards the drinking well. Support your arguments with simple drawings. (8 marks)