Wednesday, April 2, 2008 : 1:40 p.m.

Regional-Scale Chemical Evolution of Groundwater in the Wilcox Aquifer, Northern Mississippi Embayment

Estifanos Haile and Alan E. Fryar, University of Kentucky

This study aims to integrate groundwater geochemistry and numerical modeling to evaluate groundwater residence time within the Wilcox aquifer in the northern Gulf Coastal Plain. We are focusing on the confined section of the aquifer (with well depths ranging between 116 and 518 meters) along the regional flow path, which extends from the subcrop of the Wilcox Group in southeastern Missouri to the farthest downgradient municipal wells southwest of Memphis. Along the flow path, we observed increases in pH and temperature, a lack of O2 (27 wells ≤ 1.0 mg/L) and NO3- (undetectable in 23 wells), a prevalence of Fe (18 wells > 0.3 mg/L), decreases in Mn and SO42-, and increases in CH4. Ca2+ concentrations gradually decreased as Na+ increased. We infer that calcite dissolution in the upgradient section, cation exchange downgradient, redox reactions, and possibly mixing control solute chemistry. Values of δ2H and δ18O (-42 to -28‰ and -6.8 to -5.1‰ [V-SMOW], respectively) are slightly enriched with respect to the global meteoric water line (MWL) and fall along a regional MWL for Paducah, Kentucky. The stable isotopes show two distinct, gradual enrichments along the flow path, for which there are two plausible explanations. First, the north-south increase in values is consistent with increasing proximity to the moisture source area (the Gulf of Mexico). Second, increasing enrichment with distance from the recharge area in a confined aquifer is consistent with paleoclimatic variations (i.e., depletion of the isotopic composition of recharge over time). To resolve these two explanations, estimate residence time and assess cross-formational leakage, we plan to use 36Cl,and temperature in numerical models of groundwater flow coupled to solute transport and heat flow.

Estifanos Haile, University of Kentucky EDUCATION Ph. D., Geology, University of Kentucky (UK), ~Dec 2008 Licentiate, Hydrogeology, Royal Institute of Technology (KTH), Sweden, 2005 B. Sc., Geology, Addis Ababa University, Ethiopia, 1998 WORK EXPERIENCE Jan 2006 – present: Teaching Assistant, UK. Dec 2002 to Dec 2005: Teaching and Research Assistant, KTH, Sweden. Sep 1998 – Aug 2000: Graduate Assistant, University of Asmara, Eritrea.


2008 Ground Water Summit