Abstract Two pilot-scale permeable reactive barriers (PRBs) were installed in an acidic terrain to treat contaminated groundwater with low pH and high concentrations of Al and Fe. The first pilot-scale barrier (PRB-1) was installed in 2006 using recycled concrete aggregates (RCA) as the reactive material, and the second barrier (PRB-2) was installed in late 2019 using limestone aggregates (LA) as the reactive material. Although the initial material cost of the recycled concrete aggregates is low, laboratory trials conducted before the field applications deduced that limestone is capable of more reliable and efficient pH neutralisation in the long term, reducing frequent maintenance or material replacement in the PRB. The performance of PRB-1 has been monitored continuously over the past 14 years. In particular, both internal (within PRB) and external (upgradient and downgradient) variations in acidity (pH), ion concentrations, and the flow conditions, including the piezometric heads, have been analysed. These decade long field observations have resulted in a comprehensive understanding of the temporal variations of treatment by RCA along the groundwater flow path through the alkaline granular mass and its biogeochemical clogging. For instance, acid neutralisation at the entrance of PRB-1 decreased by 31% over 14 years, whereas the corresponding reduction at the outlet is only 6%. The non-homogeneous biogeochemical clogging in different PRB zones was evident by a 48% reduction in hydraulic conductivity at the inlet and a 34% reduction at the outlet.