By T.P. Schrader
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During the spring of 2001, water levels were measured in 427 wells in the Sparta-Memphis aquifer in Arkansas and the Sparta aquifer in Louisiana. Water-quality samples were collected
for temperature and specific-conductance measurements during the spring and summer of 2001 from 150 wells in Arkansas
in the Sparta-Memphis aquifer. Dissolved chloride samples were collected and analyzed for 87 of the 150 wells. Water-quality samples were not collected in Louisiana. Maps of areal distribution of potentiometric surface, difference in water-level measurements from 1997 to 2001, and specific conductance generated from these data reveal spatial trends across the study area. The highest water-level altitude measured in Arkansas was 328 feet above National Geodetic Vertical Datum of 1929 (NGVD of 1929) in Grant County; the lowest water-level altitude
was 197 feet below NGVD of 1929 in Union County. The highest water-level altitude measured in Louisiana was 235 feet above NGVD of 1929 in Bienville Parish; the lowest water-level altitude was 218 feet below NGVD of 1929 in Ouachita Parish.
The regional direction of ground-water flow in the Sparta-Memphis aquifer in Arkansas generally is to the south-southwest
in the northern half of Arkansas and to the east and south in the southern half of Arkansas; the ground-water flow in the Sparta aquifer in northern Louisiana generally is in an easterly direction toward the Mississippi River. Four cones of depression
are shown in the 2001 potentiometric-surface map, centered
in Columbia, Jefferson, and Union Counties in Arkansas and Ouachita Parish in Louisiana as a result of large withdrawals
for industrial and public supplies. A broad depression exists in western Poinsett, Cross, and St. Francis Counties in Arkansas.
A map for water-level changes from 1997 to 2001 was constructed using water-level measurements from 278 wells. The largest rise in water level measured in Arkansas was about 35 feet in Prairie County. The largest decline in water level measured in Arkansas was about 93 feet in Columbia County. The largest rise in water level measured in Louisiana was about 23 feet in Jackson Parish. The largest decline in water level measured in Louisiana was about 33 feet in Claiborne Parish.
Hydrographs were constructed for wells with a minimum of 25 years of water-level measurements. A trend line using a linear regression was calculated for the period of record from spring of 1976 to spring of 2001 to determine the annual decline or rise in feet per year for water levels in each well. The hydrographs
were grouped by county or parish. The median values for county and parish annual water-level decline or rise ranged from -1.57 to 0.29 foot per year.
Specific conductance ranged from 16.8 microsiemens per centimeter at 25 degrees Celsius in Ouachita County to about 1,470 microsiemens per centimeter at 25 degrees Celsius in Lee County. The median specific conductance was 340 microsiemens
per centimeter at 25 degrees Celsius. Dissolved chloride concentrations ranged from 1.4 milligrams per liter at a well in Lincoln County to 250 milligrams per liter at a well in Lee County. The median dissolved chloride concentration was 7.7 milligrams per liter.
Contents III
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