ISOTOPE TRACING IN GROUNDWATER APPLICATIONS (original) (raw)

Isotope methods in hydrogeological studies of Finnish shallow glacigenic formations have been developed and applied at the Geological Survey of Finland (GTK) since the late 1990s. The Laboratory for Isotope Geology has analyzed oxygen and hydrogen isotopes in water samples on a routine basis since 1995, and the isotopic composition of inorganic carbon and strontium dissolved in water since 2000. The first detailed records on spatial and annual variability in the isotopic composition of precipitation and groundwaters in Finland were generated during 1995 to 2005. GTK has three active precipitation stations related to the Global Network of Isotopes in Precipitation (GNIP) programme operated by the IAEA. Isotope "fingerprinting", based on the isotopic difference between interacting water reservoirs, has been useful in several applied studies related to water management, especially artificial recharge (AR). At Tuusula Waterworks in southern Finland, the isotope ratios of oxygen and hydrogen have been utilized to calculate the mixing ratios between local groundwater and infiltrated lake water, and the carbon isotope method to quantify the processes of organic matter removal in artificial groundwater recharge. To understand the response of the natural groundwater system to artificial recharge and the mixing of infiltrated water with local groundwater, knowledge of the geochemical baseline and isotopic characteristics of the aquifer is essential. In the Virttaankangas groundwater formation, SW Finland, isotopic applications in AR have had a significant role in the planning of infiltration and monitoring of the active water plant, as well as assisting in the calibration of groundwater flow model. New isotope approaches for hydrogeology are being tested using the facilities of the Finnish Isotope Geology Laboratory (SIGL). Separation method for cations such as lithium, magnesium, calcium, strontium, lead and uranium are currently under development. The automated separation methods would significantly reduce the throughput time of samples. In contrast to oxygen and hydrogen, the isotopic differences in dissolved components in water are inherited from organic and inorganic atmospheric, industrial and anthropogenic sources, together with weathering processes during the interaction between minerals, soil and water.