Cutoff Walls to Contain Petroleum Contaminated Soils

Cutoff walls and other barrier systems have a long history of use in traditional geotechnical construction for the control of water seepage, flows, and pressures. With the increased awareness of the hazard posed by contaminated soils and groundwater, it was a natural step to employ barrier wall systems to contain and prevent the spread of contaminants. However, the criteria for successful performance of a barrier to contain a contaminant plume are, in general, much stricter than the criteria for a barrier to control water in traditional geotechnical construction. For example, in traditional geotechnical construction, cutoff walls are typically required to reduce water flows or control water pressures so that they are not problems during construction or operation of a facility. As a consequence, small seeps and flows may be acceptable and measures to accommodate small flows and bleed off slight pressures are incorporated in the design. In contrast, a barrier called upon to contain a contaminant plume should ideally permit no passage of contaminants or at least permit passage of contaminants at such a slow rate that the material escaping does not constitute a hazard. The impact of the chemistry of the permeant on the properties, particularly hydraulic properties, of the barrier must also be assessed when the barrier is required to contain contaminants. Most cutoff walls in traditional geotechnical construction must only deal with water with a relatively narrow range of chemistries. On the other hand, barriers used to contain pollutants can encounter a much wider range of pore fluid chemistries which are often much more chemically aggressive than unpolluted water. This chapter examines various cutoff wall systems available from the perspective of construction-related defects and interaction with contaminants.