Rit (Vísindafélag Íslendinga) - 01.06.1976, Side 153

The samples are all collected as outflow from the top of the wells.
In the case of the wells G-4 and G—5, samples have heen collected
and measured regularly for their deuterium content over longer
periods. The obtained values apparently do not change with time.
The rms deviations for G-4 and G-5 are approximately the same as
the accuracy of the measurements. We have therefore reason to
believe that the reservoir is large and well-mixed.
Furthermore, as the wells in this area all give water with similar
ðD-values, in spite of differing depths, ranging from 48 m to 2200 m,
it is likely that the area is only fed by one type of groundwater.
15. 10.2 ElUSaár.
In the Elliðaár area, the hydrology seems to be much more com-
plicated than in the Laugames area.
The lowest 5D-value, 8D = — 64.4%0, was found in the well G—23
when it was only 534 m deep. G-23 is located farthest to the north
in the Elliðaár area. When the well was 1266 m deep, samples col-
lected at various depths gave 8D-values ranging from — 60.9%0 to
— 63.6%0, where the 5D-value decreased with depth. Thus both the
uppermost and the deepest aquifers seem to discharge water with
the lowest 5D-value which is not far from that obtained for the
Laugames area. The water pumped out of the hole gave 8D =
- 62.0%0.
Going from G-23 to the south, the water recovered from the
wells seems to increase in deuterium content. The highest value,
5d = — 59.2%0, is found in the two southernmost wells, G-31 and
H-20.
The Cl“ content of the southemmost wells in the Elliðaár area is
~ 15 mg/1 and the silicate content is ~ 130 mg/1. Therefore the
chemistry is similar to what would be expected if this water has
reacted with igneous rocks at a temperature of about 90-100°C, the
same as actually measured in the wells.
Therefore it seems very likely that the Laugarnes and the Elliðaár
area receive water from two groundwater systems with 8D = — 65 %0
to — 66%0 and 8D = — 59%0 to — 60%0 respectively. The boundaries
between these two systems are apparently found in the northern-
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