Contaminant displacement caused by polyurethane grouting in the deep vadose zone

Area of Science:

• Environmental Science
• Geotechnical Engineering
• Chemical Engineering

Background:

• The deep vadose zone (DVZ) presents challenges for contaminant remediation due to its depth.
• Chemical grouting, specifically polyurethane grouting, is explored for contaminant immobilization in the DVZ.
• A key concern is the potential for grouting to mobilize and disperse contaminants.

Purpose of the Study:

• To investigate contaminant displacement during polyurethane grouting in the DVZ.
• To evaluate the effectiveness of soil desiccation and soil freezing in mitigating contaminant displacement.
• To understand the role of soil water content and polyurethane curing gas production in contaminant mobility.

Main Methods:

• Laboratory-scale polyurethane grouting tests were conducted.
• Contaminant displacement was measured under different conditions.
• Soil desiccation and soil freezing were implemented as pre-treatment methods.
• The influence of polyurethane resin gas production rates on contaminant displacement was analyzed.

Main Results:

• Polyurethane grouting immobilized approximately 9.1% ± 3.5% of contaminants.
• Soil desiccation reduced contaminant displacement to 2.3%.
• Soil freezing showed limited effectiveness in reducing displacement, attributed to flushing and gas production during curing.
• Higher gas production rates from polyurethane resins correlated with increased iodide displacement ratios.

Conclusions:

• Polyurethane grouting is a viable method for contaminant immobilization in the DVZ.
• Soil desiccation is an effective strategy to minimize contaminant displacement during grouting.
• Controlling gas production during polyurethane curing is crucial for preventing contaminant mobilization.