Explain how groundwater can become polluted

Groundwater is a water under the surface of the Earth. It is widely used as a source of freshwater. Thanks to its underground position, it is not as much vulnerable to pollution such as surface water. However, some leaking of landfills, septic systems and agricultural chemicals that can reach it deep down under the surface can cause groundwater pollution.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.