The picture above illustrates organization of the vertical section of a wellbore. It is important, first, to appreciate the scale; the producing formations (or production zone) are thousands of feet deep, whereas the groundwater aquifers are typically only hundreds of feet deep. Also note the multiple layers surrounding the wellbore. In addition to the several layers of steel that compose the conductor pipe and surface, intermediate and production zone casings, each of these layers (except for certain sections of the intermediate casing) is encased with cement through the zones that they traverse. If the integrity of these barriers is maintained, wellbore-groundwater aquifer communication is prevented.