Oxygen profiling of the unsaturated zone using direct push drilling

Area of Science:

• Environmental Science
• Geochemistry
• Soil Science

Background:

• Accurate dissolved oxygen (DO) measurements are vital for understanding soil processes and groundwater quality.
• Traditional methods for in-situ DO profiling in the unsaturated zone can be complex and invasive.

Purpose of the Study:

• To develop and validate a novel methodology for in-situ oxygen profile measurements in the unsaturated zone.
• To assess the performance and reliability of the developed method under laboratory and field conditions.

Main Methods:

• A direct push drilling technique was employed using sampling liners with integrated silicone septa.
• Oxygen measurements were conducted by puncturing the septa with a retractable optode needle featuring a fluorescent tip.
• Method validation involved laboratory tests across various oxygen concentrations and soil water contents, followed by field demonstrations.

Main Results:

• The method demonstrated high accuracy, with relative standard deviations below 5% even in water-saturated soils.
• Successful deployment in a complex soil aquifer treatment system yielded DO profiles down to 30 meters with 1.5 m spatial resolution.
• A single sensor facilitated over 50 field measurements, indicating good durability, though recalibration was needed approximately every 30 measurements.

Conclusions:

• The developed methodology offers a reliable and efficient approach for determining dissolved oxygen profiles in the unsaturated zone.
• This technique has significant potential for environmental monitoring, hydrogeological studies, and soil remediation assessments.
• Further research may focus on optimizing sensor longevity and recalibration frequency for extended field applications.