Hårdhetsvariation i grundvatten längs Badelundaåsen ... - Midvatten

ABSTRACT
Hardness variation in groundwater along Badelunda esker between Leksand and Avesta
Manuel Entrambasaguas
Water hardness indicates the concentration of calcium and magnesium ions in water. Water
with high concentrations of these ions is described as hard water and water with low
concentrations is described as soft water. Water that is too hard or too soft can lead to
technical and economical problems. In collaboration with Midvatten AB, groundwater
hardness in the Badelunda esker between Leksand and Avesta has been mapped, and an
attempt has been made to explain the variations. For this purpose, different GIS programs,
such as ArcView, ArcInfo, IDIRISI, and one geochemical modelling program, PHREEQC,
has been used. GIS programs were used for digitising geological and hydrological maps and
then for combining them with other kinds of data. Simulations of chemical equilibria have
been accomplished using PHREEQC.
The absolutely most important factor that affects groundwater hardness is dissolution of
carbonate minerals. The dissolution is controlled by access to these minerals and pH value of
groundwater. Soil samples taken along Badelunda esker indicated the presence of carbonate
minerals, and showed significant variation in carbonate content. PHREEQC simulations have
indicated that samples from most of wells were saturated with calcite, it means there is no
lack of carbonates. The simulations indicated even the importance of carbon dioxide pressure
for pH and hardness in groundwater. Because this pressure is much higher under the ground
than in the atmosphere the pH value will change as soon the water comes in contact with
atmospheric air. Measurements of pH in field are quite complicated and are not usually
performed in the field. In this work, pH values were obtained from laboratory analyses, and
no measurements were made in the field.
Also road salt effects hardness. From several wells located closely to way 70 were received
data showing rising chloride contents and hardness during last 30-40 years. The direct effect
of road salt on hardness (exchange of Ca 2+ by Na + ) was investigated using simulation in
PHREEQC. Results of simulations showed that effect of road salt on groundwater hardness
are of secondary significance.
In some cases, extreme values in groundwater hardness could be explained by infiltration of
surface water or by the occurrence of relict seawater.
Key words: Hardness, groundwater, calcium, magnesium, GIS, Badelunda, esker.
Department of Earth Sciences, Uppsala University, Villavägen 16 ,SE- 752 36 Uppsala
ISSN 1401-5675