Abstract
The Mississippi Embayment Regional Aquifer Study
groundwater-flow model was used to simulate the potential
effects on future groundwater withdrawals at five powerplant
sites—Gleason, Weakley County, Tennessee; Tenaska,
Haywood County, Tennessee; Jackson, Madison County,
Tennessee; Southaven, DeSoto County, Mississippi; and
Magnolia, Benton County, Mississippi. The scenario used in
the simulation consisted of a 30-year average water-use period
followed by a 30-day peak water-demand period. Effects
of the powerplants on the aquifer system were evaluated by
comparing the difference in simulated water levels in the
aquifers at the end of the scenario (30 years plus 30 days) with
and without the combined-cycle-plant withdrawals. Simulated
potentiometric surface declines in source aquifers at potential
combined-cycle-plant sites ranged from 56 feet in the upper
Wilcox aquifer at the Magnolia site to 20 feet in the Memphis
aquifer at the Tenaska site. The affected areas in the source
aquifers at the sites delineated by the 4-foot potentiometric
surface-decline contour ranged from 11,362 acres at Jackson
to 535,143 acres at Southaven. The extent of areas affected
by potentiometric surface declines was similar at the Gleason
and Magnolia sites. The affected area at the Tenaska site was
smaller than the affected areas at the other sites, most likely
as a result of lower withdrawal rates and greater aquifer
thickness. The extent of effect was smallest at the Jackson
site, where the nearby Middle Fork Forked Deer River may
act as a recharge boundary. Additionally, the Jackson site lies
in the Memphis aquifer outcrop area where model-simulated
recharge rates are higher than in areas where the Memphis
aquifer underlies less permeable deposits.
The potentiometric surface decline in aquifers overlying
or underlying a source aquifer was generally 2 feet or less at
all the sites except Gleason. At the Gleason site, withdrawals
from the Memphis aquifer resulted in declines of as much as
9 feet in the underlying Fort Pillow aquifer. The simulated
potentiometric surface change occurring in the Fort Pillow
aquifer appears to be the result of leakage through the Flour
Island Formation separating the Memphis and Fort Pillow
aquifers where this confining unit is thin, sandy, or absent.
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First posted August 22, 2012
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