Sediment Associated Arsenic in Stream and Aquifer Sediments

Authors

Christopher N. Elofson, University of Nebraska Lincoln

Date of this Version

Spring 2017

Document Type

Article

Citation

Environmental Studies Undergraduate Student Thesis, University of Nebraska–Lincoln, 2017

Comments

Copyright © 2017 Christopher Elofson

Abstract

Arsenic (As) is an element commonly associated with aquifer sediment, with a global concentration 1.7 mg/kg, and can be subsequently released into groundwater. In recent times, increased anthropogenic inputs have contributed to geochemical changes in the subsurface that affect the mobilization of arsenic into subsurface water resources. Concentrations above the EPA’s maximum contaminant level (MCL) of 10 µg/L have recently been reported in many areas across the United States, including Nebraska. The health risk of prolonged exposure to high arsenic concentrations are skin ailments, like hyper pigmentation and keratosis, and cancer. Furthermore, many rural communities, especially in western Nebraska, lack the resources to treat their drinking water supplies. Recent studies have indicated As concentrations above the MCL in Wauneta, NE, a small community in western Nebraska. Wauneta is quite concurrent with other well-studied As contaminated regions but exhibits some important hydrological and geological differences including the presence of oxidizing groundwater, carbonate-rich sediments, and the influence of Frenchman Creek, which flows through the town. Sediment geochemical analyses revealed two sources of As: 1) As derived from Frenchman Creek and 2.) As sourced from the aquifer sediments. Sequential extraction experiments indicate that sediments contain as much as 4.22 mg/kg As and have the potential to contaminate the groundwater up to 99.75 µg/L. Speciation experiments also exhibit high, easily mobilized, sediment associated arsenic concentrations in Frenchman Creek, providing potential for the impact of surface-groundwater interactions on the quality of Wauneta’s drinking water. This is a significant health risk to Wauneta and others using this aquifer for drinking water.