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How does an earthquake affect groundwater levels and water quality in wells?

Groundwater levels in wells can oscillate up and down when seismic waves pass. The water level might remain higher or lower for a period of time after the seismic waves end, but sometimes a long-term offset of groundwater levels follows an earthquake. The largest recorded earthquake-induced offset in a well is a one meter rise. 

Water quality can also be affected by earthquakes, typically in locations where the shaking was at least strong enough to be felt. Well water might become turbid as shaking dislodges loose sediment from pores and cracks in the rocks supplying water to the well. This is often temporary, lasting only hours or days. More serious impacts on water quality can occur when strong earthquake shaking damages sewer lines, gas lines, or any infrastructure containing hazardous materials, releasing contaminants into the water. 

Scientific sampling of spring and well water before and after earthquakes often shows small chemical changes, indicating that earthquake shaking can increase permeability below the surface and connect aquifers with nearby formations containing water with different chemistry.  These changes are generally too small to be detected without specialized equipment and are unlikely to pose hazards to human health. 

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