Aquifers over uk.
What's under the ground in the UK.........we call these formations
Green:
hold plenty of water of exceptional quality straight out of the
ground.
Pale Brown:
Plenty of water but harder to extract. More technical
drilling.
Pale green:
Rock small extraction and limited supplies.
Very pale
green: Mudstone, sandstone. Reasonable supplies but elevated iron.
Light blue:
shelly sands sometimes salty.
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Areas like London are built on clay however under the clay lies the chalk ...see below.
Erosion over millions of years took away the chalk hills where London sits today and replaced it with clay.
We can still access the chalk by drilling to around 100 metres through the clay.