Experimental study on the reliability of column tests for the design of permeable reactive barriers

Permeable reactive barriers (PRBs) represent an established technology for treatment of contaminated groundwater. Column tests can give indications on how an in situ PRB will perform and are used for barrier design. Since PRBs have a lifespan from several years to a few decades, in order to reduce column tests duration, they are usually accelerated respect to in situ conditions increasing contaminants mass discharge through the column either augmenting the contaminated groundwater flow rate or the concentration of contaminants or both. The objective of this paper is to evaluate the influence of hydraulic flow rate and of initial nickel concentration on column tests results and therefore to assess if the acceleration of the column tests lead to results sufficiently reliable to be used for PRBs design. Tested reactive media are a granular mixture between ZVI and Pumice and ZVI used alone. The contaminant studied is nickel an heavy metal rather common in contaminated sites and particularly difficult to remove. The column tests demonstrated how accelerated ones are often non sufficiently representative of in situ conditions especially regarding the reproduction of the PRB long term hydraulic conductivity.