Glacial sediment causing regional-scale elevated arsenic in drinking water.

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Elevated arsenic concentrations in public drinking water are a concern in the upper Midwest, USA.
• Arsenic contamination in groundwater can pose risks to public health.
• Understanding the source and transport of arsenic is crucial for effective water management.

Purpose of the Study:

• To investigate the association between glacial drift provenance and arsenic concentrations in public drinking water systems.
• To identify the characteristics of specific glacial sediments that contribute to arsenic mobilization.
• To highlight the phenomenon of arsenic-impacted groundwater not requiring high-arsenic sediment.

Main Methods:

• Statistical analysis of public water system data and geological mapping of glacial drift.
• Characterization of sediment properties, including grain size and organic carbon content.
• Evaluation of geochemical mechanisms responsible for arsenic mobilization in groundwater.

Main Results:

• Public water systems within the footprint of northwest provenance late Wisconsin-aged drift show significantly higher rates of exceeding the U.S. EPA arsenic standard (12%) compared to outside the footprint (2.4%).
• Both glacial drift and shallow bedrock aquifers are affected by arsenic contamination associated with this drift.
• The fine-grained matrix and organic carbon in this drift promote reductive mechanisms that mobilize arsenic.

Conclusions:

• The lateral extent of northwest provenance late Wisconsin-aged drift is a key factor in elevated arsenic concentrations in upper Midwest drinking water.
• Arsenic-impacted groundwater can occur due to sediment characteristics that mobilize arsenic, not solely from high-arsenic parent material.
• Utilizing existing statewide data is valuable for identifying and characterizing regional environmental issues like arsenic contamination.