Groundwater of meteoric origin

The chemical characteristics of groundwater of meteoric origin change systematically in the direction of flow in a gravity-induced groundwater flow system (Bredehoeft et al., 1982 Collins, 1975 Herczeg et al., 1991 Tdth, 1980). The... 

Increase In basinwatd extension of groundwater of meteoric origin due to tall in sea level... 

Fig. 9.7 Isotopic composition of groundwaters of northern Chile. The values lie below the meteoric line of local precipitation, explained by the investigators (Fritz, et al., 1979) as reflecting secondary fractionation by evaporation prior to infiltration, or the presence of ancient waters that originated in a different climatic regime. The large variations in the groundwater compositions are useful in local groundwater tracing.

The stable isotopic compositions of these waters (5D SMOW and 5 0 SMOW) indicates that all the groundwaters are meteoric in origin (Fig. 7). Water sampled from the granite at DH-4/80 m contained detectable tritium (4.6 TU). 

Analysis for such isotopes as carbon and deuterium has been conventionally used to assess the relative age of groundwater, and in evaluating its origin (i.e., meteoric, juvenile, formation, etc.), chemistry, and total salinity. Isotope composition of ground-water and surface water has also been used to correlate between areas of precipitation and groundwater, thus providing an indication of source area(s) of recharge. 

The meteoric line is a convenient reference line for the understanding and tracing of local groundwater origins and movements. Hence, in each hydrochemical investigation the local meteoric line has to be established from samples of individual rain events or monthly means of precipitation. A specific example of a local meteoric line, from northeastern Brazil, is given in Fig. 9.5. A local meteoric line is obtained 5D = 6.4 <5180 + 5.5 (Salati et al., 1980). Examples of equations of local meteoric lines reported from various parts of the world are given in Table 9.1. 

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