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IIIBD'llllt
(g) Group C waters are found in dolomite, the Ventersdorp System, the Pretoria shales
and in the basic rocks of the Bushveld Igneous Complex.
Group D: Soda carbonate waters
(a) TDS values are variable in the range 245 - 700 mg r 1 •
(b) The Si0 2 content is generally very high ranging from 12 - 18%.
(c) With the exception of Red granite waters, the chloride content is very low.
(d) With the exception of the Upper Beaufort waters, the 804 content is very low.
Even in the Beaufort waters, the SO4 content is not very high.
(e) The chief characteristic of these waters is the very high soda alkalinity, which
usually ranges from 15 - 38% (as Na2C03) and is due to NaHC0 3 .
(f) In terms of the CaO : MgO ratio, there is generally more calcium than magnesium,
except in certain Old granite waters.
(g) The pH varies between 7,4 - 8,2.
(h) In terms of hardness Ca(HC0 3 )2 and Mg(HC0 3 )2 seldom exceed 50% (as CaC0 3 ).
(i) These waters can be regarded as a sub-group of Group C (likewise carbonate
waters). The only difference is that the alkalinity in Group C is mainly due to
Ca(HC0 3 )2 and Mg(HC0 3 )2 whereas in Group D waters there is in addition, an
appreciable amount of sodium bicarbonate and sometimes sodium carbonate.
There is a considerable degree of overlap between the waters of Group C and
Group D.
(j) Waters of Group D arise in the Middle and Upper Beaufort beds, the Stormberg
sediments and lavas, Red granite, the Pilansberg alkali rocks, and in the Old granite
of the northern Transvaal.