As many will remember, the Portland Water Bureau issued a boil water notice over the 2009 Thanksgiving weekend that was the result of a positive hit on a routine test for E coli in the Washington Park reservoir. State law dictates that a second test follow the initial hit, and if that test is positive, a boil water notice is issued for affected customers. In that case, the follow up test came up positive, and the boil water notice was issued. Since that incident was the first boil water notice of its scale for the Water Bureau, much was learned in the process, and a number of changes to the Bureau's process were made.
One major change that occurred in the aftermath of that event was a new protocol which requires that the Water Bureau immediately shut down the affected reservior after any positive sample for E coli. Although this has impacts on the hydraulics of the system and challenges our water operations folks, it confines any potential issue within the affected reservoir and takes the potentially affected water out of service, thereby minimizing any potential risks.
On Tuesday, Water Bureau sampling of Reservoir 1 at Mt. Tabor came back positive for E coli, and 23 minutes later, Reservoir 1 was taken off line as a precaution while the State mandated follow-up samples were tested. Fortunately, the follow up samples came back negative, so no boil water notice was necessary. Reservoir 1 will be drained and cleaned, and brought back into service ASAP.
Although the positive sample for E coli was not routine, it has occurred 16 times in the open reservoirs since the bureau began testing for it in the 1990s, and our experience last November caused us to be much more aggressive in minimizing any potential risks. Most of the time, as in this case, positive hits are anomalies that are not confirmed by follow up tests.
This experience is an excellent illustration of the Water Bureau's vigilance in making sure Portland's water is clean and constant, and their performance in this circumstance was outstanding.
Posted by: TK