Virginia Earthquake Could Affect Some Water Wells

What happens above the Earth's surface was dramatically apparent recently in places from Mineral, Virginia, to Washington, D.C., but what's not so obvious are impacts beneath the surface to groundwater, said the National Ground Water Association.

While it's too early to assess in Virginia and surrounding environs, earthquakes commonly cause fluctuations in groundwater levels and damage to water wells systems, said NGWA Public Awareness Director Cliff Treyens.

"Since aquifers are water-bearing subsurface formations, it makes sense that water levels and wells would be affected," Treyens said. "One well driller after a California quake cited a well that produced 60 gallons per minute prior to a moderate earthquake slowing down to ‘practically nothing' after."

Sometimes the reason for such impacts is obvious. In bedrock formations, for instance, the well will be drilled until it hits a fracture or crevice that holds water. A moderate earthquake could easily alter that configuration, Treyens said.

Aquifers consisting of unconsolidated materials can compact, or become unstructured as a result of the seismic energy moving though them during the earthquake, in a process called "liquefaction." This results in a loss of storage for groundwater and subsidence on the ground's surface.

While surface structures are often designed to be earthquake resistant, the same cannot be said of water well construction. The result is that often wells are destroyed. Earthquakes also can affect groundwater quality, sometimes causing turbid well water.

There is one other earthquake/groundwater connection less well known. Water wells can actually function as seismometers of sorts.

In a sense, water wells can reflect the Earth tide, which is a separate, but related, phenomenon to the ocean tides. The Earth is "pulled" by the Moon much in the same way the ocean is. This "surface tide" can cause the water in a well to go up and down in the hole, referred to as oscillation. This oscillation can occur in the aftermath of an earthquake.

A water well in Christianburg, Virginia, has become renown, picking up 200 large earthquakes around the world since real-time monitoring began in 2004.

NGWA, a nonprofit organization composed of U.S. and international groundwater professionals — contractors, equipment manufacturers, suppliers, scientists, and engineers —is dedicated to advancing groundwater knowledge. NGWA's vision is to be the leading groundwater association that advocates the responsible development, management, and use of water.

SOURCE: National Ground Water Association