Jökull - 01.12.1982, Side 89

ínilow into the drillholes is commmonly obtained
when dykes are crossed or in scoriaceous horizons
near to dykes. The dykes can probably act both as
impermeable barriers and as permeable channels,
depending on how fractured they are. Most of the
main aquifers are found to be connected with dykes
and this is used when the drillhole locations are
chosen (Bjömsson 1981). Only a few dykes in a dyke
system are connected to aquifers.
The íirst drillhole cutting the main aquifer at
Laugaland yielded in the beginning 100 1/s of free
flowing water. During production the water level
has been lowered 200 — 300 m by pumping. The
other areas in Eyjafjördur seem to act in a similar
way, being one of the most impermeable regions
used for house heating on big scale in lceland.
CHEMISTRY OF
THE GEOTHERMAL WATER
The general features of the geothermal water in
the region (Table 1) arelowcontentoftotaldissolv-
ed solids and a high pH. Due to the Iow contents of
dissolved solids the variation in contents of some
substances is too low for a safe detection.
I he water is in equilibrium with calcite (Fig. 2a)
us expected when geothermal water has reacted
with the underground rocks. The relative activities
°f the major cations and protons against tempera-
ture plot nearly on a straight line (Fig. 2b) compar-
able to results from other areas in Iceland (Pálmason
etal. 1979).
0-*— 30 40 1 50 60 i 70 80 90 IÓ0 1 cholcedony °C

Fig. 3. Measured temperature against estimated
chalcedony temperature in water from drillholes.
The points are water sampled at well head and
crosses are samples from deep aquifers.
Mynd 3. Mœlt hitastig á móti reiknuðu kalsedonhitastigi
vatns úr borholum. Punktar eru vatnssýni Jrá holutoppi, en
krossar eru djúpsýni úr borholum.
TABLE 1. Selected analyses of geothermal water from the Eyjaíjördur region. For location see Fig. 1.
TAFLA 1. Efnagreiningar á v'óldum sýnum af jarðhitavatni úr Eyjafirði. Staðsetning lauganna er sýnd á mynd 1.
in ppm
Spt-ing or drillhole t°C pH/°C SÍO2 Na K Ca Mg co2 so2 h2s C1 F B Total dis- solved solids 6D 618 Chalce dony temp. °C Fcld- spar temp. °C
Laugaland 94 9.77/21 102.9 50.9 1.50 2.79 0.004 18.0 38.1 0.06 11.6 0.43 0.130 242 -t-99.5 - -13.32 88 108
Grýta 30 9.62/22 91.5 75.2 1.35 3.24 0.005 34.5 56.9 <0.1 29.5 0.60 0.340 302 — -12.95 86 80
Mjaðmárd. 33 9.20/21 81.0132.3 2.45 13.70 0.120 14.6 107.4 <0.1 118.8 2.17 0.62 465 -t-102.6 - -12.97 85 79
Hólsgerði 40 9.51/21 82.0 83.0 1.53 6.05 0.040 21.7 76.7 0.14 40.5 3.16 0.24 305 -í-107.5 - -14.27 74 79
^■Strjúgsá 24 9.72/21 38.0 32.4 0.27 1.58 0.023 20.2 9.0 0.07 10.3 0.40 0.06 114 h-92.5 - -12.60 28 49
Stóridalur 17 9.59/18 59.0 60.5 0.68 6.70 0.22 17.8 30.0 0.07 41.5 0.95 0.210 197 -M00.2 - -13.74 56 58
Botn 83 9.83/24 81.3 48.6 1.02 3.48 0.004 11.6 43.3 <0.1 8.3 0.60 0.143 233 -í-98.0 - -14.03 70 86
Ytri-Tjarnir 80 9.95/21 92.3 53.2 0.96 3.60 0.006 13.3 43.0 0.09 11.4 0.47 0.160 223 -102.2 - -14.12 75 79
Garðsá 19 9.82/22 57.0 54.5 0.55 4.74 0.004 17.5 47.9 0.03 19.6 0.38 0.200 202 -—99.2 -13.55 50 53
Glerárgil 55 9.83/20 78.1 48.7 0.72 2.16 0.059 13.8 31.2 <0.1 8.8 0.60 0.190 218 -i-100.3 - -14.09 58 71
noi measured
JÖKULL 32. ÁR 85