The document analyzes the water resources and hydrochemistry of the alluvial and Sparta aquifers in the Grand Prairie region, focusing on issues of ground-water level declines and salinization. It details objectives to delineate water quality conditions and presents findings showing that while salinization is not widespread, varying hydrochemistry results from geochemical evolution rather than ground-water declines. The study provides baseline data for water users and suggests future work involving statistical analyses and comparisons with other datasets.

1. Water resources and hydrochemistry of the Alluvial and Sparta aquifers of the Grand Prairie region Chad D. Cooper, Ralph K. Davis, Kenneth F. Steele University of Arkansas, Department of Geosciences Arkansas Water Resources Center

2. The Problem Multiple ground-water uses Ground-water level declines Critical Ground-Water Area as of 1998 Salinization may be related to ground-water level decline Water-quality variations resulting from lower water levels can impact all uses

3. Objectives Delineate spatial distribution and magnitude of varying water quality conditions as related to areas of ground-water level decline Determine areas of ground-water salinization (high in chloride, SpC, TDS) Examine varying water-quality conditions spatially over the study area Provide baseline water-quality data to water users of the region

4. Physiography of Study Area Approximately 8,900 square kilometers Little to no relief Dominated by agricultural production

5. 1999 Land Use/Land Cover (summer)

6. Water level, Alluvial aquifer, spring 1998 Declines in Alluvial: 1915-1933 – up to 60 feet, Arkansas Co. 1938-1953 – from 10-20 feet 1955-1961 – from 3-10 feet 1969-1996 - 32 feet, Lonoke Co.

7. Wells completed in the Alluvial aquifer About 7,000 wells!

8. Water level, Sparta aquifer, spring 1998 Declines in Sparta: 1949 – 50 feet near Pine Bluff 1958-1965 – 160 feet at Pine Bluff 1969-1999 – 70 feet+ in Arkansas Co. 1988-1999 – almost 20 feet in Lonoke Co.

9. Wells completed in the Sparta aquifer About 325 wells (and rising)!

10. Sample Sites July/Aug 2000 78 Alluvial 39 Sparta 8 QA/QC Analyses at WQL of AWRC

11. Ground-water quality, Alluvial aquifer Good to acceptable Calcium-magnesium-bicarbonate type No MCL’s exceeded SMCL’s exceeded: Mn (0.05 mg/L) Fe (0.3 mg/L) Chloride: 3-172 mg/L

12. Ground-water quality, Sparta aquifer Better Range from Ca-Na-HCO 3 type to Na-HCO 3 type No MCL’s exceeded SMCL’s exceeded: Mn (0.05 mg/L) Fe (0.3 mg/L) Chloride: 2-56 mg/L

13. Salinization related to declines? Cl, Alluvial Aquifer Cl, Sparta Aquifer

14. Salinization related to declines? TDS, Alluvial Aquifer TDS, Sparta Aquifer

15. Spatial trends, Sparta aquifer GW FLOW Lonoke Jefferson Arkansas Prairie

16. Spatial trends, Sparta aquifer Ionic Strength Calcium Saturation

17. Spatial trends, Sparta aquifer Transect Location Results GW FLOW

18. Spatial trends, Alluvial aquifer Conductivity vs. Well Depth

19. Spatial trends, Alluvial aquifer Ionic Strength Calcium Saturation 37 of 78 samples saturated

20. Spatial trends, Alluvial aquifer pH vs. Ca Saturation pH~6.85

21. Spatial trends, Alluvial aquifer pH vs. Iron pH~6.85

22. Results and Conclusions Salinization not widespread Water quality for both aquifers: Alluvial: Acceptable, with high Cl and Fe Sparta: Better, lower Cl and Fe Varying hydrochemistry not result of ground-water level declines Varying hydrochemistry is instead result of geochemical evolution along flowpath

23. Results and Conclusions Dominant processes: Alluvial: Ca saturation, precipitation of calcium- and iron-rich cements Sparta: Ca saturation, precipitation of calcium-rich cement; cation exchange Future work: Combine and compare with other datasets from the region Statistical analysis of spatial data Examine relationships with rivers Iron in the Alluvial aquifer?

24. Acknowledgements Arkansas Water Resources Center (AWRC) Water Quality Lab, AWRC Arkansas Soil and Water Conservation Commission United States Geological Survey, Little Rock Arkansas Department of Environmental Quality Center for Advanced Spatial Technologies, University of Arkansas

25. Questions?