The history of the Etowah Water Bank began about 540 million
years ago during the Cambrian Age. This was a time when
northwest Georgia was covered by a vast expanse of seas in which
thick sequences of sedimentary rocks were deposited. Millions of
years later, two of the many tectonic plates comprising the
earth’s crust began to collide. The sea that previously
separated these two plates was underlain by thick layers of
limestone and dolostone. The collision caused the limestones and
dolostones of northwest Georgia to crumble together like an
accordion, squeezed between layers of granite and other hard
rocks in the earth’s crust. This created faults and folds, some
of which caused local ground levels to rise and form mountains
while in other areas the ground level was pushed down up to two
miles underground. This geologic process formed what we now call
the Valley and Ridge Geologic Province which extends through
northwest Georgia and into Alabama and Tennessee.
Erosion and weathering over millions of years formed the Coosa,
Oostanaula, Coosawattee, Etowah and Chattahoochee river basins.
The infiltration of rainwater into the limestones and dolostones,
and other geochemical processes, opened up porous holes,
solution channels and caves. These porous rocks underlie about
1,000 square miles beneath portions of Polk, Bartow, Floyd and
Gordon counties and also beneath portions of Chattooga, Walker
and Catoosa counties in northwest Georgia. They are called the
Knox Dolomites, the Shady Dolomites and the Conasauga Limestones.
While they extend to depths of several thousand feet, practical
and economic considerations suggest that water storage in the
upper 1,000 feet of these formations would be useful. Properly
designed and located wells in these formations tend to have high
yields and produce good quality water, however the aquifers have
typically not been used for drinking water supply purposes since
the area’s water supply needs have been met using surface
reservoirs, nearby streams and rivers, and large springs.
Furthermore the dolomites are very hard, requiring special well
drilling equipment and careful design. Some communities in
northwest Georgia produce a small portion of their drinking
water needs from local wells and springs, such as Calhoun and
Catoosa County Water System, however most of the local drinking
water supplies are from surface water from rivers and also from
reservoirs such as Lake Allatoona and Lake Lanier.
In some areas of northwest Georgia the aquifers are unconfined,
exposed at land surface, with typical depths to the water table
of a few tens of feet. In other areas aquifers are overlain by
other formations and are therefore confined. Both of these areas
are of interest for the Etowah Water Bank, storing water when it
is available during wet periods and recovering water when
needed, such as during severe droughts.
Faced with the growing need for sustainable, reliable water
supplies, more than 80 communities, farmers and industries
nationwide are now storing drinking water underground in wells
such as those proposed by the Etowah Water Bank. These wells are
in confined and unconfined aquifers; fresh, brackish and saline
aquifers; and at depths ranging from less than 100 feet to as
much as 2,700 feet. Some of these water banks are quite large,
such as Las Vegas, San Antonio, Calleguas Municipal Water
District in southern California and the Kern Water Bank in
southern California. Others are as small as a single well.
Unlike many other parts of the world where groundwater levels
are declining rapidly due to excessive production and inadequate
recharge, the Etowah Water Bank will not “mine” water. The Bank
will recover only up to the cumulative volume that has
previously been stored. In this way existing groundwater
resources in this area will be preserved and protected.
Following severe droughts groundwater levels will be quickly
restored through recharge of treated drinking water into the
Etowah Water Bank wells.
 The Etowah Water Bank also proposes to develop a large
conventional well-field in west-central Georgia, supplementing
the yield of storage facilities in northwest Georgia. Our
history in this area is younger, beginning only about 140
million years ago during the Cretaceous Age. Erosion of the
Piedmont granite rocks formed Coastal Plain deposits of gravel,
sand and clay that extend in ever-thickening layers from the
Fall Line to the Atlantic and Gulf coasts. The Fall Line is
where the Piedmont granite rocks are exposed, often forming
waterfalls, and it extends from Montgomery, Alabama, to
Columbus, Georgia, to Macon, Georgia, and on up the Eastern
Seaboard.
Approximately 1,000 square miles of Taylor, Marion, Stewart, and
Schley counties of west-central Georgia between the Flint and
Chattahoochee Rivers are of primary interest for underground
water storage purposes. Specific geologic strata include the
sands of the Tuscaloosa, Eutaw, Blufftown, and Cusseta
formations. Well depths would range from 500 to 750 feet below
land surface, including strata that are under confined or
semi-confined conditions. These strata become progressively more
brackish in a southeastwardly direction. The coarse-grained
character of these sands is conducive to high production rates.
Current there are few local water users of the aquifer system in
this area.
 During severe droughts Etowah Water Bank wells in this area
would pump water into tributaries to the Chattahoochee and Flint
Rivers, ensuring an adequate flow at the Florida State Line and
thereby protecting shellfish in Apalachicola Bay. An equal
volume of water would be reallocated from Lakes Allatoona and
Lanier to meet the water supply needs of the Atlanta area during
droughts.
The Etowah Water Bank will provide a cost-effective supplemental
supply of water to the Atlanta urban area while protecting the
downstream ecosystem needs of Florida and also sustaining
reliable water supplies for Alabama for downstream areas on the
Coosa River. In conjunction with existing and planned surface
reservoirs, the Etowah Water Bank will form and maintain a very
large subsurface reservoir, target capacity of which is 560,000
acre feet. By comparison, Lake Allatoona is about 231,000 acre
feet. Effective integration of these water sources with existing
and any new surface reservoirs will provide a reliable,
sustainable water supply for all water users. |
Carbonate Aquifers of
NW Georgia 
