Hårdhetsvariation i grundvatten längs Badelundaåsen mellan Leksand och Avesta
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 Ca2+ 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.