Page 113 - Hydrogeology Principles and Practice

HYDC03 12/5/05 5:36 PM Page 96

96 Chapter Three

BO X
Continued
3.5

Fig. 2 Hydrochemical sections showing major and minor anion (a) and cation (b) data for the sample locations shown in Fig. 1. Data
after Morgan-Jones and Eggboro (1981).

locations shown in Fig. 1. The dominant major ions in the limestone ±10% is shown to account for any errors in the chemical analyses or
−
groundwaters are Ca 2+ and HCO in the unconfined areas but in in the basic thermodynamic data used to compute the saturation
3
areas where the limestones become increasingly confined beneath indices (Box 3.6). Samples from locations in the unconfined lime-
clays, the groundwater changes to a Na-HCO type. Groundwaters stones where high Pco values are maintained under open-system
2
3
from deep within the confined limestones contain a Na-Cl compon- conditions are supersaturated with respect to calcite. The con-
2+
ent as a result of mixing with increasingly saline groundwater. sistently high Ca /Mg 2+ ratios and low degrees of dolomite
The degree of groundwater saturation with respect to calcite and saturation in the samples analysed suggest that both limestone
dolomite is shown diagrammatically in Fig. 3. A confidence limit of series contain predominantly low magnesium calcite.