CHEMICAL-COMPOSITION OF HARD AND SOFTROCK GROUNDWATERS FROM CENTRAL NORWAY WITH SPECIAL CONSIDERATION OF FLUORIDE AND NORWEGIAN DRINKING-WATER LIMITS

Groundwaters from crystalline and metamorphic rocks (hardrocks) and from Quaternary deposits, i.e., alluvial and glacial deposits (softrocks) from the counties of Nord-Trondelag and Sor-Trondelag were analyzed for major and minor elements and ions including fluoride. The median concentration of F- in water from the hardrock aquifers is 0.28 mg/l (14.7 mu eq/l) in contrast to water from softrock aquifers in which it is found to be 0.05 mg/l (2.6 mu eq/l). More importantly, ca. 15% of the locations where water was abstracted from hardrock wells contain 1.5 mg/l (78.9 mu eq/l) F- or more. Thus, 15% of all hardrock wells returned F- results that are at or above the maximum recommended value for drinking water. Of the softrock wells, none are above 1 mg/l. Geologists would normally expect higher F- contents in groundwaters derived from acid rocks, e.g., in granitic or gneissic areas. When comparing the host lithology with the observed F- contents, however, no clear relationship between F- content and lithology is visible. The highest observed F- values actually occur in gneissic host rocks. However, wells drilled in amphibolites/greenstones, mica schists, calcareous rocks, and sedimentary rocks all returned some analytical results above 1.5 mg/l F-. These results suggest that all hardrock wells drilled should be tested for F- and the users informed about the results and advised to take any necessary precautions. When applying the recently proposed Norwegian drinking water limits to our data, 51% of all softrock well waters and 56% of all hardrock well waters are unfit for consumption without prior treatment, although we analyzed only for about half of the proposed elements/parameters. This result seriously questions the concept of fixed action levels-many of them with totally unproven health implications-for so many parameters/elements for hardrock groundwaters.