Rit (Vísindafélag Íslendinga) - 01.06.1976, Blaðsíða 132

The above studies show well how ðD-measurements can be used in
order to distinguish between different aquifers in one and the same
well.
The available data also give information about the origin of the
water in the well.
Both water types contain approximately the same amount of chlo-
ride, 9500 mg/1. The mgNa+/mgCl” ratio was found to be con-
stant, approximately 0.5 in all cases where measured, indicating
oceanic origin of the chloride (Tómasson 1967). We can rule out the
possibility that the water in the well is ocean water, because of the
low 8D-value. Precipitation on the Vestmannaeyjar with 5D =
— 48 %0 is also rather unlikely. Therefore the only explanation is
that the water originates as groundwater flowing from the main-
land. To explain the high Cl" content, the water may be assumed
to pick up its salinity either on its passage through old marine
sediments or it may have mixed directly with ocean water.
Clayton et al. (1966) and Graf. et al. (1965) have shown that the
Illinois, Michigan and Alberta brines have the same or similar ðD-
values as the local precipitation. They concluded, therefore, that
the water was of a meteoric origin but the original interstitial sea
water had all been flushed out of the sediments, leaving its salt
content behind, and was replaced by rain water as a result of the
filter properties of the sediment. The deep circulating water in the
well at Vestmannaeyjar could have acquired its Cl~ in the same
way.
If we assume that the water in the Vestmannaeyjar well origi-
nates in precipitation deposited under climatic conditions similar
to those of today, the water in the upper aquifers should originate
in a recharge area on the southern lowland, but the deeper aquifers
should receive their water somewhat further inland, possibly from
the glacier Eyjafjallajökull. Fig. 34 gives a possible model of such
underground passage of the water recovered in the Vestmanna-
eyjar well.
Simple mixing with sea water as an explanation for the high Cl~
content should also be considered. Such mixing would mean, how-
ever, that the initial fresh water in the lower aquifers would have
5D = — 120%o, which is lower than any precipitation found in Ice-
land at present. In that case the “fresh water” in the deeper aqui-
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