ABSTRACT
ABSTRACT: The vulnerability of bedrock wells to microbiological contamination has been examined using microbiological data for 169 Norwegian waterworks using groundwater from bedrock. Inspections have been carried out at 49 of the 169 waterworks to identify possible causes to the recorded microbiological contamination. The microbiological water quality is correlated to (i) land use and contamination sources, (ii) type and thickness of surrounding superficial deposits, (iii) wellhead completion (including the well casing), and (iv) distance from wells to running water. Based on this study, wells are least vulnerable to microbiological contamination when the superficial deposits are 2.5 m thick and the wells are located 100 m from farmland and rivers/streams. It is recommended that the wellhead completion includes a well-house and a well casing of at least 5 m below and 0.5 m above ground level respectively. The gap between casing and bedrock should be sealed.
