E. coli contamination in Saue private wells unresolved after month-long investigation
E. coli contamination found in private wells in Saue, near Tallinn, in mid-August remains without an identified source after extensive investigation, the local municipality said.
On August 17, the municipal government received its first report of a possible water quality problem, in the northwestern part of town. Three more reports followed the next day, and residents were informed of contamination in private wells. A crisis committee convened on August 19, bringing in relevant authorities and taking the first water samples.
A total of 11 samples were taken — three from the public water supply, all found safe, and eight from private wells, seven of which were contaminated with E. coli. No contamination was found in the public supply.
Water and soil samples were taken, wastewater systems and pipelines inspected, and the Environmental Board, Health Board, Rescue Board, AS Tallinna Vesi and the Geological Survey of Estonia all involved in assessing the situation.
Drinking water tanks were set up in the town for local residents affected by the contamination.
Andres Marandi, a hydrogeologist at the Geological Survey of Estonia (Eesti geoloogiateenistus), said the evidence suggests several factors may have coincided: microbiological contamination may already have been present in the area's soil and shallow groundwater, while low summer water levels, the condition of private wells and excavation work on Rauna tänav may have affected water movement through the soil.
Deficiencies were found in on-site wastewater treatment systems at several properties, but in none of the cases could these be conclusively linked to the well contamination. A tip alleging a sewer pipe leak on Rauna tänav during construction was investigated by the Environmental Board; the municipality said isolated minor leaks may have occurred but were not extensive enough to cause widespread groundwater contamination. CCTV inspections by AS Tallinna Vesi found no broken pipes.
Repeat samples taken on September 2 showed coliform bacteria levels had fallen in several wells, indicating improvement, though the original source remains unknown. Soil samples from five locations also failed to identify a single source.
The municipal government said it would continue spot checks of well water in the affected area.
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Editor: Andrew Whyte, Valner Väino
