It also permits the use of impermeable caps to prevent hazardous material from leaking out, rather than a complete removal of industrial residues, a much more costly undertaking.

It also permits alternative methods including fences and impermeable caps to stop waters from seeping out instead of requiring their removal.

Fertilizer is then poured into the top of the pipe, which is covered by an impermeable cap resembling an upside-down water glass.

Oil likely migrated upwards during the late Pliocene, becoming trapped in the folds and structural traps of the higher rocks of the anticline which form an impermeable caps.

The standards also permit alternative methods, including impermeable caps to stop waste from seeping out instead of requiring the removal of such industrial residue.

In 1989 the site received a permanent impermeable cap.

In cleaning the site, G.M. covered part of it, mainly where the old plant stood, with an impermeable cap to stop wastes from seeping out rather than carting them off the site.

In areas where large anticlines formed, oil from deeper-lying source rocks was trapped in permeable rocks such as the limestone and dolomite underneath the impermeable cap of evaporite sediments.

Typically the best solution is to leave the ground undisturbed and to work to prevent any future disturbance of the ground by creating grout curtains and impermeable caps, then monitor for leachate.

The overlying Rincon Formation, a shale deposited in a deep-sea environment, serves as an impermeable cap.