A process for insitu treatment of at least one contaminant in groundwater, the process comprises the steps of: installing a permeable reactive barrier in the flow path of the at least one contaminant, wherein the installation of the permeable reactive barrier comprises the steps of: boring a first borehole with a portion longitudinally extending; filling the longitudinally extending portion with a reactive material comprising a solid reactant configured to react with the at least one contaminant in the groundwater to produce at least one product having less hazardous characteristics than the at least one contaminant; boring a second longitudinally extending portion and filling the second longitudinally extending portion with the reactive material.