When fresh water is withdrawn at a faster rate than it can be replenished,
a draw down of the water table occurs with a a resulting decrease in the
overall hydrostatic pressure. When this happens near an ocean coastal area,
salt water from the ocean intrudes into the fresh water aquifer as shown
in the diagram. The result is that fresh water supplies become contaminate
with salt water as is happening to communities along the Atlantic and Gulf
coasts.
