Abstract: A hazardous waste containment system for preventing the lateral migration of hazardous fluid substances (including both liquid and gas wastes, heavy metals, etc.) into the water table, particularly for sites which are located over a fluid impermeable strata (20) of clay or the like, while also allowing the controlled removal and/or in situ treatment of the fluid substances. The system uses an encircling barrier containment wall (W) comprising a plurality of slidingly engaged, sealed, interlocked, vertical barrier members (501/101) which extend down to and sealingly interface with the underlying fluid impermeable strata. At least one barrier member (1') includes a pass-through (P', FIG. 2) for one or more pipes (900) leading into an adjacent, satellite work/equipment area (E, FIGS. 1 & 3) where the hazardous fluids are controllable removed and treated on-site, and the treated fluids thereafter removed out of the work/equipment area.