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Groundwater Protection

Groundwater is water that is held within the rocks and soils below us (underground strata). Rain falling on the land seeps down into the rocks over time. It is an important source of water that can supply millions of homes and businesses and is often of a greater purity than water from rivers. Any activity occurring on land can pollute this essential resource and this is why we need to protect it.

Groundwater is found as water occupying the spaces between rock particles in special rock layers known as 'aquifers'. Perhaps the best way of imagining an aquifer is as a solid sponge. Rainwater trickling down through from the ground surface (infiltration) fills up the spaces in the rock. The water fills the aquifer from the bottom upwards, the base being an impermeable layer of rock underneath the aquifer.

The bottom part of the aquifer has all its air space replaced by water and is termed 'saturated'. In the upper part of the aquifer the rock spaces contain air as well as water, here the aquifer is called 'unsaturated'. The place where the aquifer changes from unsaturated to saturated is called the 'water table'.

A frequent misconception of groundwater is considering it as some sort of 'underground river'. Mostly this is untrue, however in some areas, for example where there are limestone caves, underground rivers can be found.

Water in an aquifer does not sit still and flows through the spaces and cracks in the rock, being pulled by gravity and pushed by the force of the water above and behind it. The water moves from an area where water enters the aquifer (a recharge zone) to an area where water exits the aquifer (a discharge zone). This movement has the effect of removing a lot of impurities from the water, filtering it through the rock so that groundwater is generally much cleaner than surface water. As groundwater is generally very clean it often requires little or no treatment before being used, the level of treatment depends on what it is to be used for. This makes groundwater a very cheap source of 'raw water' for public supply.

The flow of groundwater is slower than surface water, and the deeper into an aquifer the water is, the slower it moves. This means that if groundwater becomes polluted and the pollution moves deep into the aquifer, the water can potentially remain polluted for a long period of time.

Applying waste to land can pollute groundwater and other water underground. The risk applies in any field where permeable soils lie directly on top of rock formations that hold water, especially where the water table is shallow or the rock has cracks in it (for example shallow soils over limestone).

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