Mineral and Thermal Groundwater Resources

Groundwater has always occupied a central position in the history of civilization. In the ancient Bible Lands, a well represented a continuous supply of good quality drinking and irrigation water — a base around which a settlement could grow. The control of strategic groundwater resources in the Levant has thus been a cause of strife between nations from the days of the Patriarchs to the present conflict between Israel and its neighbours.

In the UK the bottled water fad began in earnest in the 1980s, partly as a response to the need for an ‘adult’ non-alcoholic drink, stimulated by stricter drink-driving laws, and partly as a response to public fears over the quality of British tap water. Currently, the market stands at 500 million litres annually in Britain; a market value of some £300 million (Edwards, 1994). It is not so long ago that the Englishman abroad received warnings ‘not to drink the tap water on the Continent’ , and was encouraged to consume only Evian water on holiday.

Many people regard mineral waters as something extraordinary but, in most cases, they (and here we include thermal waters) acquire their characteristic chemistry in the same way that any groundwater does. Much of the character of mineral water comes from the dissolution or leaching of components from minerals, but that is not the whole story, so let’ s start from the beginning.

The temperature of groundwater is influenced by air temperature to depths of about 50 m. Below this, additional heat is obtained from the rocks with which the water is in contact. The total amount of heat stored in the top 10 km of the earth’ s crust represents more than 5000 times the thermal energy available in world coal resources (Bouwer, 1978), but only a fraction of this is accessible.

The evaluation of mineral and thermal water systems embraces many activities, including exploration and investigation, determining whether a resource can be economically developed and monitoring both the system and its economic viability. It is emphasized that cost effective evaluation, in all its stages, must be carried out within the framework of a conceptual model of the system, which is improved as more information is collected. The activities involved often overlap in an iterative process and can rarely be separated in practice, although for reasons of length modelling of systems and exploitation of resources are discussed in Chapters 6 and 7.

At an early stage in exploration it is necessary to develop a conceptual model of the system (e.g. Figure 6.1). This provides a framework within which to plan investigations and hypotheses against which to test the data collected, as well as to plan exploitation. The usefulness of any model depends on whether it meets the users’ requirements and these must be clearly defined so that the conceptual model can be developed accordingly.

Mineral waters have traditionally been exploited at natural emergences such as springs, by wells or shafts up to tens of metres deep and more rarely by drainage galleries. Springs are often improved to protect the source and provide ready access to the water. Improvements may range in complexity from simple collection structures to the provision of storage tanks, gas bells to release gas pressure, housing built over the source (Figures I.1 and 12.1, for example) and piped reticulation systems.

Environmental issues have to be addressed in the exploration and development of mineral and thermal waters. Several problems, such as over-abstraction and pollution have already been mentioned. Here some of these concerns are drawn together and the need for a holistic approach to the management of resources is emphasized.

Iceland lies in the North Atlantic Ocean, just south of the Polar Circle. It is formed by the only major subaerial part of the Mid-Atlantic Ridge system (Figure 9.1) and has an area of some 100000km². The Mid-Atlantic Ridge is represented by the Reykjanes Ridge to the south and the Kolbeinsey Ridge to the north. The continuation of the ridge across Iceland is complex, but there are two main zones of rifting present. Of these, the western zone runs from Reykjanes northeast to Langjökull where it is connected by the Mid-Iceland volcanic zone to the eastern rift zone, which runs from Tjörnes in the northeast of Iceland to the Torfajökull area in the south. In addition, there is a WNW-trending volcanic fracture zone which runs from Snaefellsjökull to within 30 km of Langjökull. The whole island is volcanic in origin, the rocks being dominantly of basaltic composition. A mantle hot-spot is thought to lie beneath Iceland, on the grounds of the observed anomalous volcanic productivity, geochemical signature and indications from geophysical measurements of an underlying low density mantle plume (Sæmundsson, 1978).

Bad news… spas are no longer popular in England. A few have managed to continue to pull tourists in, notably Bath, Harrogate, Buxton and Matlock, but they rely rather on their rich history and architecture than on the properties of their waters. There is discussion about the possibility of opening public or private bathing establishments at one or two localities, but we will have to wait some years to see the fruit of these proposals. Britain is possibly unique among European nations in having let its rich heritage of spa waters fall into disrepair. This decline commenced in the second half of the 19th century, but the final straw came in the 1950s and 1960s when the Health Service veered away from spa therapy in favour of the application of medical drugs in more controlled forms.

Lithuania is a small but geologically varied country. With an area of 65 200 km² and a population of some 4 million, it is underlain by a relatively complete and undeformed sequence, from the Precambrian basement of the Baltic Shield up to the extensive glacial deposits of the Quaternary period. Lithuania is almost entirely dependent on groundwater for its drinking water supply; some 14000 water supply wells abstract water from 20 aquifer horizons of varying age (Paukštys, 1993). There is growing concern regarding the deterioration of groundwater quality (Juodkazis and Klimas, 1991; Juodkazis, 1994). The regional dip of the strata is to the northwest, the sedimentary pile becoming thicker towards the basin of the Baltic Synclinorium. In the west, near the Baltic Sea, the sediments are thickest, with the basement at more than 2300 m depth. In the southeast of the country, on the margins of the Belorussian Anticlinorium, the crystalline Precambrian basement is found at only 250–300 m depth. Across the border in Belorussia, the depth of the basement is as little as 100 m (Klimas, 1993).

Nordland County is a region remote from English industrial smokestacks and with an ‘ultra clean Arctic’ image. Studies of acid rain have demon- strated pH values above 5 in precipitation, which is typical for areas with little or no industrial pollution (Figure 13.1). This is in stark contrast to southern Norway, which is affected by airborne pollution from central and western Europe, and northeast Norway, which is exposed to acid rainfall from the nickel smelters on the Kola peninsula. The perceived clean conditions were an important factor when the Geological Survey of Norway (NGU), together with Nordland County Council and six municipalities, initiated a 1-year monitoring programme of seven water sources in Nordland County (Figure 13.2). The main object of this investigation was to find water sources or springs with a water quality suitable for bottling and export. Three of the sources are near-coastal high mountain lakes, remote from human activity; two springs emerge from Quaternary deposits while the remaining two are Palaeozoic limestone karst springs. The fieldwork and water sampling were carried out from November 1992 to February 1994, and included

Despite the small area of its territory (90 000 km²), the Czech Republic can be, in a certain sense, considered a nation of abundant hydrogeological resources. More than 100 mineral water springs are exploited and several thousand others are registered. In particular, the extremely diverse geology of the Bohemian Massif is reflected in the huge variety of its different types of mineral groundwaters. For example, cold acidic springs occur in very close proximity to thermal or radioactive mineral waters, high in H₂S and arsenic. The ‘balneal triangle’ of west Bohemia has acquired a worldwide reputation due to the famous spas of Karlovy Vary, Mariánské Lázně and Františkovy Lázně (Figure 14.1).

The spa town of Buziaş is situated in the southeastern part of the Romanian Plain, at the border between the plain and the hills of Banat, about 30 km southeast of Timiçoara (Figure 16.1). Mineral waters are found in the upper terrace of the Timiş river along the Salcia Valley, which has a maximum width of 8 km. The waters here are similar in character to those of Spa (Belgium), Royat (France) and Bad Pyrmont (Germany).

Thermal gradients of 40–55°C/km, slightly higher than the continental average, occur in the eastern section of the Pannonian Basin, in Romania. Some 15 low temperature (50–85°C) geothermal well fields (Figure 16.1) exploit aquifers in the Pliocene detrital formations, at depths ranging between 900 and 2000 m (Plaviţă and Cohut, 1990, 1992).