The International Information Center for Geotechnical Engineers

Permeable Reactive Barriers - Disadvantages

DISADVANTAGES (of all the types)

The main disadvantage of the Permeable Reactive Barrier is that there is limited information about long term performance of the PRB in-situ. (Olson & Higgens, 2009) Since PRBs have only been created in the field since 1991, there are limited amounts of full-scale case studies. Also many of these case studies have been determined to be impacted by the method of construction. Another secondary disadvantage for the PRB is the sensitivity to the accuracy of construction, which can be difficult to determine at depth. For example, if a boulder is encountered and not removed the flow of the contamination can evade the PRB. (Richards, 2008)

Table 3 Disadvantages

Table 3: Disadvantages of using a PRB (Bronstein, 2005)

As mentioned previously in the Design section, the width of the barrier is a function of basic hydrology (groundwater velocity and hydraulic conductivity) and residence time between the reactive media and the contaminant(s). Limited understanding of the complete flow regime such as directional changes with changing seasons can reduce the effectiveness of the PRB. (ITRC, 2005) Changes in geochemistry from reactions such as mineral precipitation or pH changes can significantly reduce the hydraulic conductivity and result in PRB failure. (Wilkin et al., 2009)

Reactive Material Disadvantages

Zero Valent Iron- The lifetime of this material can be reduced due to the contamination coating the surface of the ZVI particles, preventing flow through the barrier due to this build-up. (Thiruvenkatachari et al., 2008) The iron reactivity could also be reduced if it comes into contact with silica or natural organic matter. (Thiruvenkatachari et al., 2008) Also the ZVI increases the environmental impact of the PRB due to the creation of the material itself being an energy intensive process. (Olson & Higgens, 2009)

Granular Activated Carbon- Due to GAC being used less in PRBs than ZVI, there is limited data on in-situ treatment under field conditions. Also the performance of the GAC is highly dependent on temperature and other extrinsic parameters. (Thiruvenkatachari et al., 2008) As with the ZVI, surface coating may decrease adsorption capacity of the GAC. This decreased capacity will caused the GAC to be less efficient in removing the contamination from the groundwater if the design does not account for the change in adsorption capacity.

Limestone- Limestone barriers need to account for lime’s slow reaction time when coming into contact with the contaminants. (Thiruvenkatachari et al., 2008) Contaminants coating the lime particles with iron precipitates also caused a loss in efficiency of the barrier. (Thiruvenkatachari et al., 2008) Lime is affected by extrinsic parameters such as pH levels. Lime is not effective in acidities higher than 50mg/L. (Thiruvenkatachari et al., 2008)

Long-Term Performance 

The long-term performance of PRBs is highly dependent on the site characteristics he long-term performance of PRBs is highly dependent on the site characteristics, flow patterns, and interactions between the contaminant plume and reactive media. Lifetime can be reduced due to unintentional precipitation of constituents either in the water or as contaminants, biofouling, and reduced reactivity of the PRB. (Bronstein, 2005) The ITRC looked at previous PRB applications and noted, "These lessons include reduced permeability due to construction, variability in the reactive media, aquifer heterogeneity, and the permeability contrasts affecting the groundwater flow." (ITRC, 2005)

 

 

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