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Sylvi Gaut, Geological Survey of Norway; NTNU (Norway)
Lucy Robertson, Norwegian School of Veterinary Science (Norway)
Bjørn Gjerde, Norwegian School of Veterinary Science (Norway)
Atle Dagestad, Geological Survey of Norway (Norway)
Bjørge Brattli, Norwegian University of Science and Technology (Norway)
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To increase the knowledge about the vulnerability of groundwater wells in bedrock to microbiological contamination, a PhD study was initiated by the Geological Survey of Norway in 1998. Part of this study was dedicated to investigate the possible presence of Cryptosporidium and Giardia in water from bedrock wells.
A total of 20 water samples were collected from 20 different waterworks. Each sample consisted of 10 litres of raw-water. Waterworks with groundwater wells situated close to possible contamination sources for Cryptosporidium and Giardia, such as septic tanks, arable land and pasture, were specially selected for this study. Sampling took place in April and May 2004, and the US SPA Method 1623 was used to analyse for Cryptosporidium oocysts and Giardia cysts.
Cryptosporidium oocysts, but not Giardia cysts, were detected in the groundwater from 3 of 20 waterworks. In each positive sample, only one oocyst was found.
The low number of oocysts/cysts can be related to sampling in the spring, as the parasites are not likely to survive in the Norwegian terrestrial environment over winter. In addition, coliforms are more often detected in the groundwater from July to September. This might well be the case also for Cryptosporidium and Giardia, due to similar contamination sources. The lack of Giardia cysts in the groundwater samples can be due to the larger size of the cysts (10-15 m) and/or a more rapid decrease in viability than the oocysts (about 5 m).
Cryptosporidium are detected in the groundwater. This shows that at least groundwater from bedrock wells close to contamination sources is susceptible to contamination from this parasite. However, no conclusions can be drawn for Giardia. Further studies are therefore recommended to provide more reliable data. These studies should comprise groundwater from wells in both bedrock and superficial deposits, and both single, private wells and waterworks should be included. Sampling should take place throughout the year to investigate seasonal changes in the occurrence of the parasites.
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