USGS using magnetic fields to map underground
U.S. Water News Online
SAN ANTONIO -- Geologists are making a map of the
11-county-wide groundwater aquifer that supplies Texas' largest
A plane chartered by the U.S. Geological Survey is conducting an
aeromagnetic survey of the limestone and other rock layers that make
up the Edwards Aquifer. San Antonio is the largest city in the
country to rely solely upon such an underground reservoir for
municipal water supplies.
The subterranean map to be completed after several weeks' work may
help locate wells for monitoring water quality and quantity and small
dams to boost recharge to the aquifer. Its levels have dropped in
past summer droughts, cutting flow to Comal and San Marcos Springs
where threatened and endangered species live.
Crews in a Piper Navajo owned by Spectra Exploration Geoscience
Corp. of Calgary, Canada are making the survey with technology used
by the U.S. Navy to hunt submarines and by American companies to
explore for oil, gas, and mineral deposits.
The planes fly out of Hondo Municipal Airport, recording patterns
in the Earth's magnetic fields to map geological features as deep as
20,000 feet below the surface.
Of particular interest to geologists and hydrologists are
locations in Uvalde County and elsewhere where magma penetrated
Edwards limestone to form barriers to the present-day flow of water.
``Being able to better identify the ones we can't see on the
surface will help us understand the flow paths,'' said Geary
Schindel, the Edwards Aquifer Authority's chief technical officer.
The USGS and San Antonio Water System are paying Spectra a total
of $120,000 to conduct the low-level flights, which could be
completed within three weeks. Analysis likely will take at least six
Parts of Bexar, Uvalde, and Medina counties are the first to be
``It's not necessarily pinpointed at the Edwards [Aquifer]. It's
the structure the Edwards limestone is sitting on,'' said George B.
Ozuna, a hydrologist and chief of the USGS office in San Antonio.
Return to the
U.S. Water News Archives page
Return to the U.S. Water
Use a comma to separate e-mail addresses:
Hi, I thought you might like to read this article.