The International Information Center for Geotechnical Engineers

Permeable Reactive Barriers - GAC Computer Modeling Case Study, Italy


The following is a summary of Armando Di Nardo’s findings of a model PRB case study: (Di Nardo et al., 2010)

Background and Site Description

This case study uses a contaminated site in Campania Italy as a background example for a model design of a PRB. This site had a source of eight million tons of urban and special wastes (legal and illegal). The aquifer is located at a depth of 35-40m beneath the ground surface. The groundwater aquifer was contaminated with inorganic and organic pollutants. For example, the PCE concentrations are approximately 20 times higher than Italian regulatory limits (1.1 μg/l).


PRB Design

The author used computational fluid dynamics software to model the water flow through and around the barrier. The barrier considered would be a continuous trench penetrating the aquifer at the full depth of 50m, so that most of the flume was captured. Numerical simulations were used to determine the optimal barrier position and dimensions in relation to the contamination distribution. The best results were a barrier that was 3m wide to account for the required residence time and 900m long to ensure the entire plume was captured.

Case study Italy overview

An overview of the contamination flow through the modeled site from the report



During the numerical run period of about 60 years, the out-flowing concentrations were always lower than the regulatory limit. This result suggests that adsorption barriers can be considered for the remediation of the Campania site. Before implementation, a more thorough investigation is required into some technological aspects, pollutant synergy and long term effects. 

Case study Italy Figure 3

A figure demonstrating the concentrations prior to the barrier (Cin) and the downgradient values (Cw)


Discussion and Conclusions

A problem that the modeling software results showed is that if the inflowing concentrations of the PCE vary, a desorption phenomena may occur within the barrier when the PCE concentrations are lower than equilibrium. A solution to this issue is to use a wider barrier to ensure that a gradual release of PCE occurs, avoiding critical out-flowing concentrations. Therefore the barrier must be designed both to retain intense concentration peaks and to ensure long term performance.

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