8.1.5. Ground water

Ground water is found between layers of geological formations such as clay, silt, sand or gravel and sandstone. A body of underground water is called an aquifer. They are replenished primarily by rainwater, either directly as it infiltrates a porous area straight into the ground or indirectly from adjacent aquifers. The rate of replenishment can vary greatly and determines how much groundwater is available from an aquifer.
An aquifer may be bounded by permeable formations such as sand or gravel or impermeable layers of clay or shale. Permeable aquifers are targeted by bore drillers, and will yield varying qualities and quantities of water.
Aquifers bounded by impermeable layers become confined under pressure, and are known as artesian (or flowing under pressure) aquifers. The Great Artesian Basin is one such aquifer that can be tapped into to form free-flowing bores.
The level in the soil profile below which groundwater is found is called the watertable. The depth of the watertable varies from above-ground in places to hundreds of metres below ground level in others. This means if landholders need to sink a bore to establish a reliable water supply for livestock and domestic use, it is difficult to predict the depth the bore will need to be to secure a supply of aquifer water of the necessary quality and quantity. As a result, the cost of sinking, casing and equipping a bore can vary significantly.
In the mid-Murrumbidgee catchment area, state water authorities, hydrogeologists (both government and private consultants) and contract bore drillers provide information and services to locate suitable bore sites and construct bores for landholders.