Groundwater

What is groundwater?

Most people are taught about the water cycle at school, learning that water evaporates from the oceans, condenses into clouds and then falls on the land surface as rain, before flowing into rivers and back into the sea. Often groundwater is overlooked as part of this cycle but in practice it is an essential part of the cycle that can offer access to a clean and plentiful water supply.

Rainfall, as well as flowing directly into rivers soaks into the soil, providing essential water for plants to grow. Any water that is not taken up by the plants will soak into the ground further through a process called infiltration. This water seeps through the soil and downwards through rocks. This process can be likened to water being held in a sponge. As the water travels through the rock the lower section becomes saturated, this point is called the water table.

Water will travel through the ground from the point at which it was infiltrated until it reaches a point of discharge which in most cases is a spring or river.

The water table depth is dependant on the type of rocks that form the ground conditions of any given site. Some rocks are impermeable, meaning that water can hardly flow through them, where as many rocks are permeable with small holes allowing water to flow through them. These permeable rocks that contain groundwater are called aquifers. The holes in the rocks can be between small grains of rock such as sandstone or through fissures (cracks) in rock such as chalk.

Consequently, the depth to which you drill to install a borehole is dependant on the rock type and water table depth. Before drilling a borehole the geological strata of the proposed site is assessed by our in house team and a drill depth proposed dependant on these factors. The borehole is always drilled at least 30m below the water table to allow for draw down as the water gets pumped to the surface.

Why groundwater is a good choice for a water supply?

There are numerous reasons that make groundwater a good choice for a water supply.

• Groundwater is often present where there is limited access to surface water sources.
• The quality of groundwater is usually very good. The infiltration process of water travelling through rock helps remove any pollutants.
• Groundwater supply is less affected by seasonal changes in weather than surface water supply. In the warmer, drier summer period the groundwater is less affected than surface water supply. Groundwater responds slowly to changes in rainfall meaning water is still abundant in the warmer months when it is likely that more water is needed.
• It’s a cheap water supply solution.

Up to 20m3 per day can be abstracted from the borehole without consent or license. Payback periods can be as little as 12 months.
To find out more please visit the UK Groundwater Forum website where you will find a wealth of information.