Inventering av bergborrade brunnar för dricksvatten i område med risk för salt grundvatten
en utredning av grundvattensituationen i Vreta-Ytternäs i Uppsala kommun
The city of Uppsala and its surroundings are a very expansive area. A prerequisite for a sustainable development of the area is well-functioning supply of drinking water. In Uppsala municipality, the Uppsala esker and Vattholma esker are the groundwater storages for drinking water. Besides the eskers, other sources of qualitative groundwater in the Uppsala municipality are relatively poor and more than half of the area consists of ground conditions with a risk of saline groundwater. The neighbourhood of Vreta-Ytternäs is situated 10 km south of Uppsala, in the area with risk of saline groundwater but outside the municipal water supply. In mid 20th century, the region was generally used as a recreational area with mainly cottages as residencies. In the late 20th century, houses made for permanent use were built and nowadays they have their own drinking water supply, consisting mostly of drilled wells. This makes the Vreta-Ytternäs area dependable of qualitative groundwater. Together with Uppsala municipally environment office, this study has been made in order to investigate possible saline contamination in the ground water used as drinking water in Vreta-Ytternäs. Together with water samples, data consisting of depths of the wells, age, water capacity and geographical location were collected in order to compare with saline concentration. Out of 183 wells, 56 water samples were gathered and analysed, which gives the response rate of 30 %. In order to analyse the content of saline in the drinking water, the chloride concentration was measured. The critical limit of chloride was determined to 50 mg/l. Chloride concentrations of 50 mg/l or more were found in 29 % of the wells. Even though the association was slightly positive, significance was not reached between increasing concentration of chloride and wells with rising age, higher water capacity or increasing depth. Nor a geographic correlation between the wells with a specific chloride concentration was found. In general, high concentrations of chloride (in average 54 mg/l) were detected in the area, which proves the theory regarding Vreta-Ytternäs being a high-risk area for saline contaminated water. This information about the drinking water quality is useful for the residents in the area, whom are planning to build a well. The information is also helpful for the environment office when they make assessments of building permit applications.