The present invention is directed to a waste or environmental containment system that includes modified asphalt specifically designed for containment, and a system of installation that provides a seamless cap over the area to be contained. The modified asphalt of the present invention has a permeability less than 1.times.10.sup.-8 cm/sec and an air void content less than 3 percent. The system of installation includes joint designs that meet the same parameters as the modified asphalt mat to provide a seamless containment cap or liner to contain hazardous wastes at RCRA, Superfund sites, waste sites and environmental containment areas.