Response surface methodology (RSM) was applied to evaluate the effect of the main operational variables, including initial pH, initial chromium ion concentration, bulk density of GAC and time on the removal of hexavalent chromium Cr(VI) from contaminated groundwater by permeable reactive barriers (PRB) with acid-modified granular activated carbon (GAC) as an adsorbent material. The removal rates of Cr(VI) under different values of these parameters were investigated and results indicated high adsorption capacity at low pH and low initial metal ion concentration of Cr(VI), but the bulk density of GAC slightly influenced the process efficiency. According to the ANOVA (analysis of variance) results, the model presents high R2 values of 94.35% for Cr(VI) removal efficiency, which indicates that the accuracy of the polynomial models was good. Also, quadratic regression models with estimated coefficients were developed to describe the pollutant removals.