Järnets förekomst i grundvattnet i isälvsavlagringar i Dalarna
Bakgrundshalter och rörmaterialets inverkan vid grundvattenprovtagning
A study has been performed that investigates the variation of iron content in groundwater.The study was initiated by Midvatten AB, which noticed that the iron content in groundwater samples can vary greatly over small distances. The purpose of this study was to geochemically and geohydrologically determine the factors that influence the content of iron and manganese in groundwater from a selection of eskers in Dalarna, and determine how to best sample groundwater with the method used by Midvatten AB. An evaluation was made of how the vertical variation in soil material, water composition, pumping time and pipe material affects the content of iron in groundwater. Piper diagrams were used to study the relationship between the chemical composition of the groundwater and the content of iron and manganese in groundwater samples from the studied areas. The groundwater from the studied areas was then classified in the Piper diagrams, according to the content of the major ions. Correlations were then studied between the classification and depth below groundwater table, depth below ground surface, pH, iron- and manganese content.Field samples were collected from Lennheden in order to investigate the effect of vertical variations of soil material, pumping time and pipe material on the content of iron and manganese. This was also performed to evaluate the best way of sampling groundwater. The groundwater was sampled from a steel pipe and a plastic pipe. Redox potential, pH, dissolved oxygen, iron content, temperature in groundwater, turbidity and conductivity were measured for different depths and pumping times in field.Also a groundwater sample from every sampling depth was sent to a laboratory for analysis. Diagrams and correlation tables were used to analyze these results. No correlation between iron and the major ions in groundwater was found in the Piper diagrams, but the content of manganese in groundwater had a tendency to increase with increasing alkalinity. The results from sampling groundwater showed that the average content of iron in groundwater was 0,11 mg/l from the steel pipe and 0,01 mg/l from the plastic pipe. Turbidity has the greatest effect on the analyzed content of iron in groundwater, thus the turbidity needs to be zero while sampling. A suggestion is that while investigating groundwater quality in large areas, iron pipes can be used. When the best place is located, plastic pipes can be used when the iron content needs to be investigated in detail.