The SNARC facility lies near the western outcrop
of the aquifer in central Arkansas in a transitional area between
calcium-bicarbonate-type waters near the aquifer outcrop and
sodium-bicarbonate-type waters to the south and east (Renken,
1998). The WARU facility is southeast of Stuttgart, over the central
downdip region of the aquifer which yields sodium-carbonate-type
waters with a higher total dissolved solid content than waters to the
north and west. Aquifer material in the downdip region contains
lignite—a soft coal derived from compressed peat. Lignite in the Sparta
Sand Aquifer originated from vegetation deposited with fluvial sands
during late Eocene construction of the delta systemthat was eventually
buried to become the aquifer (Waldron et al., 2011).