PRB Design
Develop durable permeable reactive barrier concepts using the right media, residence time, and constructability strategy for long-term plume interception and treatment.
Design, performance, and ZVI applications for permeable reactive barriers
A permeable reactive barrier (PRB) is an in situ groundwater remediation technology that treats contamination passively as groundwater flows through a subsurface treatment zone. PRBs are installed across the path of a plume so groundwater can continue to flow naturally while contaminants are reduced, transformed, or immobilized inside the barrier.
When designed correctly, PRBs provide long-term treatment with limited operations and maintenance, making them especially attractive for consultants seeking durable, low-energy remedies.
Ideal Use
Well-defined plumes that can be intercepted hydraulically and benefit from passive long-duration treatment.
Core Media
ZVI is the most common PRB medium for CVOCs, metals, nitrate, and sulfate treatment.
How a PRB Works
- Groundwater flows through the permeable reactive zone rather than around it.
- The reactive media treats contaminants during subsurface residence time.
- No continuous pumping or energy input is required once the barrier is installed.
Role of Zero Valent Iron (ZVI)
ZVI is the most widely used PRB media because it drives abiotic chemical reduction reactions.
- Chlorinated solvents such as TCE and PCE are reduced toward ethene and ethane.
- Soluble metals such as hexavalent chromium can be reduced to less mobile forms.
- Polyatomic anions such as nitrate and sulfate may also be treated.
- Important note: intermediate compounds such as DCE or vinyl chloride may form temporarily but are typically further degraded in a properly designed barrier.
PRB Design Considerations
| Design Factor | Key Considerations |
|---|---|
| Barrier Configuration | Continuous trenches are best for shallow plumes reachable with excavation equipment. Funnel-and-gate systems can help direct groundwater in lower-permeability settings. Injection-based PRBs can be installed deeper than trenching allows. |
| Reactivity of the ZVI | Reactivity should be evaluated for the specific iron media and contaminants involved, typically using batch or column testing and a Kmass framework. |
| Thickness of Reactive Zone | Commonly 3 to 5+ feet, depending on ZVI reactivity, groundwater velocity, contaminant concentration, and required residence time. |
| Hydraulic Conductivity | The barrier should be equal to or more permeable than the surrounding aquifer to prevent bypass. |
| Residence Time | Controlled by media reactivity, barrier thickness, and groundwater velocity. Residence time is critical for complete treatment. |
| Longevity Factors | Performance depends on iron reactivity, groundwater geochemistry, and potential mineral precipitation or fouling. |
Performance and Longevity
Well-designed PRBs can provide 3 to 15+ years of treatment performance, stable long-term plume control, and minimal decline when properly engineered. They are particularly effective for chlorinated solvent plumes, metals contamination, and polyatomic anions such as nitrate and sulfate.
Advantages of PRBs
- Passive system with no pumps or ongoing energy input
- Continuous treatment without repeated reinjection
- Long-term cost savings
- Proven performance across thousands of sites
When to Use a PRB
- Groundwater flow direction is well-defined
- A plume can be intercepted hydraulically
- Long-term containment or treatment is required
- Site access allows trenching or injection
When Not to Use a PRB
- Highly heterogeneous flow conditions
- Poorly defined plume geometry
- Extremely low-permeability formations unless an injected PRB approach is feasible
Hepure PRB Solutions
| Media | Use Case |
|---|---|
| Ferox PRB Trenching Media | High-iron-content media with uniform particle sizing optimized for excavation placement and long-term barrier applications. |
| Ferox Flow Injection Media | Fine ZVI media designed for injection-based PRB concepts where trenching is not feasible. |
Technical support and design assistance: Hepure can support site data review, feasibility evaluation, lab testing coordination, quantity estimation, and guidance on barrier configuration and installation strategy.