Ty Nant Water Geology

Warning: This section is long and is intended for those with a deep and profound interest in rocks.

In Xanadu did Kubla Khan a stately pleasure-dome decree: where Alph, the sacred river, ran through caverns measureless to man.

The Aquifer

Everyone has heard the term "water table" and most will take it to mean the level at which water collects and resides underground. This is in fact quite true. But many also share with Coleridge the idea that underground water occurs in vast lakes lying in caverns, where only the sound of a gentle gurgling and trickling can be heard in utter darkness (Read excerpt from: The Hobbit). They picture the water as flowing from one lake to another along underground rivers. Successful wells or boreholes they imagine, are those which intersect these lakes or rivers, unsuccessful ones are those which encounter only solid rock. The art of the water diviner

or "dowser" is seen as predicting the location of these postulated subterranean watercourses, and so selecting a site for a borehole where water will be struck, (the water diviner can in fact locate water, but it may not necessarily be in the form of an underground lake!). These popular misconceptions probably arose because the only places where it is possible to see underground water in its natural state are the spectacular caverns which occur in hard limstones, such as those at Dan-yr-Ogof in Wales. It is not possible to see underground water where it occurs in its most common state, percolating and residing in the minute pores of underground rocks.

Rocks of the Earth's Crust

There are three main types of rock:

• Igneous, formed by the cooling and solidification of lava, or magma, billions of years ago, which are generally non-porous
• Metamorphic, which are formed by the alteration (by heat and pressure), of other rocks (e.g. Igneous)
• Sedimentary, formed by consolidation of small particles resulting from the weathering of other types of rock.

A Special Case

Rocks that hold water are termed aquifers and the best aquifers are to be found in sedimentary rock formations, as these are the most porous and therefore able to hold a large amount of water. The transmissivity (volume throughput) of water through sedimentary rock is rapid in comparison to less porous rocks. This property is crucial for aquifers that are used to supply drinking water. It allows

the extraction of large quantities of water without depleting the long-term supply, because recharge of the aquifer takes place on a short timescale. Aquifers of low permeability, such as those in the Sahara Desert, may hold large quantities of water, but since they are relatively impermeable, once water is extracted, depletion takes place. This form of water extraction is called mining; once the water is drawn it takes thousands of years to replace it.

The Water Cycle

Quality

Variences in porosity and transit times through the aquifer determine the quality or composition of dinking water. Analysis of any source of water will reveal varying amounts of dissolved minerals, and it is these that give the water its quality and taste. Very slow transit times lead to prolonged contact with the minerals inside the rock and therefore more are dissolved by the water. Very permeable aquifers will have very quick transit times and correspondingly the content of dissolved minerals will be low.

The Source Aquifers of Ty Nant

Ty Nant Natural Mineral Water has unique characteristics. This is not surprising from a hydrogeological perspective, due to the unique character of the region's underlying geology. Although the geology of Wales is both interesting and complex, it may for simplicity be generalised into two main formations: metamorphic and igneous, both very old geologically. These two types make up the vast majority of subterranean rock found in Wales, each of which form very poor aquifers in terms of transmissivity. However, within these formations are to be found units of high permeability rock, making them ideal for water extraction. One such subterranean rock stratum forms the source aquifer for Ty Nant. Effectively surrounded by rocks of very low transmissivity, the water contained in the Ty Nant aquifer will primarily

consist of recharge directly through the surface of the ground above. Lateral flows into the aquifer from the surrounding, relatively low permeability rock is insignificant, allowing for the isolation of the aquifer. As the rocks forming the Ty Nant aquifer unit are of high transmissivity, residence times for the water are low, producing the characteristically low mineral content of Ty Nant Natural Mineral Water. Furthermore, recharge to the aquifer is rapid, allowing for a high water yield to be drawn without over exploiting the available capacity of the aquifer. Ty Nant prides itself as being the custodian of this very precious and essential resource. Having created a successful international distribution network for the water drawn from the aquifer at Bethania, Ty Nant is totally committed to ensuring the long-term preservation of what truly is a marvellous and worthy resource: the production of pure spring water from solid rock!