Mexico City, Venice, Tokyo, and Bangkok. Tens of meters of subsidence have
been documented. Building foundations can fail, underground pipes can burst,
and there can be flooding of low-lying areas. The so-called Leaning Tower of Pisa
is perhaps the world’s most famous example of subsidence caused by the great
weight of the tower differentially compacting groundwater out from only a meter
or two beneath the surface.
Groundwater pollution is a problem that becomes increasingly salient as more
human activities take place over shallow groundwater supplies. There are myriad
ways in which groundwater can be contaminated to the point where it is nonus-
able. These include infiltration from septic tank leaching fills, landfills, animal fee-
dlots, and accidental spills of materials. Additionally, injections of toxic wastes
down wells, the spread of agricultural chemicals on crops, and the leakage of
underground storage tanks can compromise the groundwater supply.
Groundwater 167