The aquifer has no shield of impermeable clay and the proposed artificial barriers would not guarantee success.

Another question, I wonder, is whether the shallow groundwater that was mentioned came from above or below the impermeable clay.

On top of the liner come two feet of impermeable clay, followed by one more foot of soil.

The decision was based primarily on the risk of contamination to the South Yorkshire aquifer, which has no shield of impermeable clay.

Geologists have identified four other major aquifers separated by relatively impermeable clays or other strata at various levels below the surface aquifer.

The underground structure of Sawston is the same as that of the region - permeable chalk and impermeable clay.

The soil of this region includes layers of sandstone and limestone acquifers separated by impermeable clay.

Additionally, the San Joaquin Valley has a shallow aquifer bounded by impermeable clays.

We'll need a bunch of rock, various sizes, dirt in quantity and most important, some good impermeable clay.

There is also sometimes a layer of impermeable clay.