Rapid growth in the Atlanta urban area has outstripped
locally available water supplies. Since 2001 water levels in
existing surface reservoirs have twice dropped to very low
levels, creating great concern regarding regional water supply
reliability and sustainability. Virtually all focus regarding
new water sources has been on the need for more surface
reservoirs, however environmental and other considerations
suggest considerable uncertainty about whether these are viable.
Based upon preliminary analysis of long-term climatological
records, and with the current population, such droughts are
expected about once every ten years. With increasing population
a greater drought frequency will become more common. Measures
need to be implemented to address these concerns.
The potential exists for development of supplemental water
supplies through underground storage in carbonate aquifers of
northwest Georgia. Recharge will be accomplished through aquifer
storage recovery (ASR) wells, storing treated drinking water
during times when excess water is available, and recovery of
water from the same wells when it is needed. The ASR technology
is now being applied at more than 80 wellfields nationwide in
about 20 states, plus several other countries. The largest is
for Las Vegas Valley Water District, with a peak recovery
capacity of 157 MGD (480,000 AFY). ASR wellfields are, in
essence, water banks. ASR wells will supplement the yield,
sustainability and reliability of existing and new surface
reservoirs.
Proposed storage capacity of EWB is 560,000 acre feet (AF), with
facilities capable of recharge at daily rates up to 50 million
gallons per day (MGD) (56,000 acre feet per year, AFY) during
wet weather and other times when water supply and treatment
capacity exceeds water demand, and recovery at rates up to 250
MGD (280,000 AFY) for durations of up to two years during
droughts. By comparison, the average water demand of the Atlanta
urban area in 2000 was about 500 MGD while peak day demands were
approximately 970 MGD. EWB would significantly improve regional
water supply reliability at relatively low capital cost and
negligible environmental impact. Participation in EWB for water
storage and recovery would be open to approximately 35 public
utilities on a first-come, first-served basis, comprising a
public private partnership.
 ASR technology for storing water underground is proven and
cost-effective. This technology is now being applied worldwide
to create underground water banks, thereby storing water where
it is safe and not subject to substantial losses due to
evaporation and transpiration. ASR technology was pioneered by
EWB member David Pyne about 25 years ago, and he has written the
only book published on ASR.
An excellent opportunity for ASR storage exists in northwest
Georgia in the Valley & Ridge Geologic Province. This is a band
of carbonates that extends from New York to Alabama, comprising
the boundary of two tectonic plates in the earth’s crust.
Approximately 10 to 20 miles wide and 1.5 to 2 miles deep, these
bands of dolomites and limestones are productive and porous,
yielding high flow rates to individual wells and providing
substantial storage capacity. Within the northwest Georgia area
of interest, approximately 1,000 square miles are underlain by
these carbonates. About 600 square miles of this area is
adjacent to the Atlanta Metropolitan Area while the remainder is
sufficiently close to provide potential value for water storage
purposes. Few wells have been constructed in this area since
drilling tends to be difficult, requiring large drilling rigs
that are not commonly available. Furthermore water supplies from
surface reservoirs have historically been plentiful.
 The Etowah Water Bank (EWB) provides a viable, cost-effective
subsurface water storage option, supplementing other regional
water sources. Most of the water supply alternatives available
to the Atlanta area will need to be implemented to some extent,
so an ASR portion of the solution will supplement, not compete
with other options. Principal alternatives include additional
surface storage reservoirs, water conservation and reuse. As
water wholesale and retail rates increase in future years, some
water conservation will automatically occur, reflecting water
demand elasticity, however there will continue to be a great
need for supplemental water supplies to support expected growth
of the Atlanta urban area.
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