Thesis Defense Announcement

College of Arts and Sciences announces the Final Thesis Defense of

Alexander Sharp

for the Degree of Master of Science

March 28, 2022 at 01:00 PM in Johnson Hall , Room 216

Advisor: Deborah Leslie

Geochemical impacts of infiltration galleries on groundwater quality in a critical groundwater area of northeastern Arkansas

ABSTRACT: "Overexploitation of the Mississippi River Valley alluvial (MRVA) aquifer in eastern Arkansas has resulted in critical groundwater areas. Managed aquifer recharge (MAR) using infiltration galleries (IG) is being investigated as a strategy for sustaining groundwater resources. On-farm storage reservoir water will be injected through IG and 30 m of unsaturated zone, which provides a sand and gravel filter to remove sediment and other particles. In this study, water quality data, MRVA sediment properties, and geochemical modeling were used to predict chemical reactions, such as mineral precipitation/dissolution and metal mobilization, that are commonly associated with mineral-water reactions from surface water-groundwater interactions. Mineralogical analysis show MRVA sediment is dominated by quartz and feldspars, and sediment contains minor to trace amounts of Fe and Mn (oxyhydr)oxides that will enhance the removal of oxyanions like arsenic during infiltration. Clay x-ray diffraction data indicate there is little expandable clay in the unsaturated zone that pose risk for reducing infiltration rates and inducing reactions along the flow path. The general water quality of the reservoir varies from local groundwater. Geochemical data suggest groundwater quality following injection of reservoir water will be most heavily influenced by the dissolution/precipitation of carbonate minerals and cation exchange between Ca, Na, Mg, and Mn. Reservoir constituent levels during the injection season do not pose a contamination risk, as they generally do not exceed groundwater levels. Furthermore, the neutral pH of both the source water and groundwater, as well as the upper aquifer material, limit any threat to infiltration water quality."