Excavation vs. In Situ Soil Mixing: Choosing the Right Approach for PRBs and Barrier Walls

When it comes to groundwater containment, the right approach can make or break your remediation plan. Should you remove the native material within the alignment or mix reagents into the native soil? This blog compares excavation and in situ soil mixing for installing permeable reactive barriers (PRBs) and hydraulic barrier walls, helping you make informed decisions under budget and compliance pressures.

Why Containment Matters

PRBs and barrier walls are critical for controlling contaminant migration and meeting regulatory cleanup goals. Choosing the right installation method impacts:

• Cost: Disposal, backfill, and transportation expenses.
• Schedule: Project timelines and risk of delays.
• Compliance: Ability to meet stringent performance criteria.

Excavation: The Traditional Approach

Excavation involves removing contaminated soil and replacing it with clean backfill or engineered barrier materials.

Advantages

• Immediate removal of contamination.
• Predictable outcomes when contamination is shallow and accessible.

Limitations:

• High disposal and transportation costs.
• Significant site disturbance and restoration needs.
• Substantial effort and cost for water removal or treatment
• Longer timelines, especially for large treatment zones.

In Situ Soil Mixing: The Innovative Alternative

Reactive media (for PRBs) or cementitious slurry (for hydraulic barriers) is mixed directly into the soil to create PRBs or barrier walls without excavation.

Advantages:

• Reduced disposal and backfill costs.
• Lower site disturbance—ideal for sensitive areas.
• Faster installation under tight schedules.

Limitations:

• Requires specialized equipment and expertise.
• Not suitable for all soil types or contaminant profiles.

Head-to-Head Comparison

When to Choose Soil Mixing Over Excavation

Soil mixing is often the better choice when:

• Groundwater flow is high.
• Soils are unstable or difficult to excavate.
• Budgets and timelines are tight.
• Regulatory compliance requires minimal disturbance.

Common Pitfalls & How to Avoid Them

• Excavation: Underestimating disposal costs, incomplete delineation.
• Soil Mixing: Poor site characterization, incorrect reagent selection.

Want to learn more about using soil mixing for PRBs and barrier walls?
Register for our upcoming webinar: Using In Situ Soil Mixing for Permeable Reactive Barriers or Barrier Walls.

Register Now >>

About the Author

Paul Lear, Ph.D.

Senior Technical Director, Civil & Environmental Construction

[email protected] 

Paul Lear, Ph.D., a leading authority in stabilization/solidification (S/S) technology, brings over 30 years of experience in full-scale remediation projects to Cascade and is leading our efforts on ISS for PFAS remediation.