Source of E. coli in Saue private wells still unknown after month-long probe
Authorities in Saue, Estonia, say they have been unable to pinpoint the source of E. coli contamination found in private wells in mid-August despite an extensive month-long investigation, though the public water supply was unaffected.
The municipal government of Saue, a town near Tallinn, Estonia, says it has not been able to identify the source of E. coli contamination discovered in private wells in the town's northwestern area, despite a month-long investigation involving multiple national agencies.
The first report of a possible water quality issue reached the municipality on August 17. Three more reports followed the next day, prompting officials to warn residents about contamination in private wells. A crisis committee was formed on August 19, bringing together relevant authorities to begin taking water samples.
Of 11 total samples collected, three came from the public water supply and were all found safe. Of the eight samples taken from private wells, seven tested positive for E. coli. No contamination was detected anywhere in the public network.
The Environmental Board, Health Board, Rescue Board, water utility AS Tallinna Vesi, and the Geological Survey of Estonia all took part in assessing the situation, examining water and soil samples and inspecting wastewater systems and pipelines. Drinking water tanks were installed around town for affected residents.
Multiple contributing factors suspected
Hydrogeologist Andres Marandi of the Geological Survey of Estonia said evidence points to several factors coinciding: microbiological contamination may have already existed 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 disturbed how water moved through the ground.
Inspectors found deficiencies in on-site wastewater treatment systems at several properties, but none could be conclusively linked to the well contamination. The Environmental Board also investigated a tip about a possible sewer pipe leak on Rauna tänav during construction work; the municipality concluded that minor, isolated leaks may have occurred but were not extensive enough to cause widespread groundwater contamination. CCTV pipeline inspections by AS Tallinna Vesi found no broken pipes.
Repeat testing on September 2 showed coliform bacteria levels declining in several wells, suggesting the situation was improving, though the original source of contamination remains unidentified. Soil samples taken from five separate locations likewise failed to point to a single cause.
The municipality said it will continue conducting spot checks on well water in the affected area going forward.
