Modeling of Plume Capture by Continuous, Low-Permeability Barriers

Modeling was performed to simulate ground water flow through reactive barriers of lower hydraulic conductivity than the surrounding aquifer to determine the plume capture widths. As a plume approaches such a barrier, it spreads laterally. Therefore, to intercept an entire plume, the barrier must be wider than the upgradient width of the undisturbed plume. The results indicate that, for practical values of barrier thickness and plume width, hydraulic conductivities ten-fold less than that of the aquifer can be accommodated by making the width of the barrier approximately 20% greater than the upgradient width of the plume. Barrier hydraulic conductivities one-hundred-fold less than that of the aquifer may require barrier widths up to twice the width of the upgradient plume for plumes 100 feet wide (33 m) and as little as 1.1 times for plumes 1000 feet wide (325 m). The results presented here lend support to the view that novel emplacement methods that create zones of slightly lower hydraulic conductivity than the native aquifer may be viable alternatives to the excavation-and-backfill approaches which have thus far been used for installing permeable reactive barriers.