Occurrence of acidic groundwater in precambrian crystalline bedrock aquifers,Southwestern Sweden

The pH and alkalinity of groundwater from 7651 wells drilled in the Precambrian crystalline bedrock of southwestern Sweden has been evaluated. The wells are generally less than 100 m deep. Analytical results were collected from different laboratories and authorities in the region. In areas with thin soil cover or coarse-grained deposits overlying the bedrock, alkalinity is normally less than 100 mg HCO₃ L^?1. Below the marine limit, where clayey sediments predominate, alkalinity sometimes even exceeds 200 mg HCO₃ L^?1. When comparing pH and alkalinity of groundwaters from Quaternary deposits with bedrock groundwaters, the latter always have higher pH and alkalinity values. The most acidic bedrock groundwaters are found in small areas close to the city of Göteborg due to additional factors of high acid loadings, high groundwater discharge and thin soil layers. A study of data from 1949 to 1985 in the province of Värmland suggests that no regional acidification of importance is in progress. However, results from public water supplies support the hypothesis that the groundwaters which are most sensitive to acidification are those where discharge from wells in small bedrock aquifers induces rapid groundwater recharge of acidic surficial water.