Lab Studies and Site Characterization for Permeable Reactive Barrier Walls
Mapping and Modeling
Following the onsite investigation, mapping and modeling can be carried out, both on the surface structures, hydrology, the contaminant loading and the geochemistry of the system. Currently, hydrologic modeling of these systems is being carried out using traditional ground water flow models. Some concern has been expressed, however, about whether these models, as currently written, can adequately describe the boundary conditions of systems such as the funnel and gate. The available geochemical models are also somewhat limited and are being used primarily to determine what ground water species can be expected to precipitate when the reactive barrier is encountered. Caution is warranted since these model reactions are usually based on equilibrium conditions that are not likely to be attained in these systems.
After modeling, predictions can be made about the variations in ground water flow and the transport and fate of the contaminant over time. Stratigraphic mapping can be used to evaluate the location and continuity of impermeable clay layers or bedrock for possible keying in of the reactive barrier. When this information has been assembled, a design decision can be made on the type of wall to be installed, the size and location of the wall, and possibly some estimates of its life expectancy. Then monitoring wells can be installed, where appropriate, with much less guesswork.