Astoria violated a federal drinking water standard this year after using a higher than normal amount of chlorine to treat organic matter in the water supply.
The city said residents do not have to boil water or take any other precautions. People who are elderly, pregnant, have an infant or have severely compromised immune systems, however, could be at increased risk and should seek medical advice about drinking city water.
The city expects to have the problem fixed by the end of December.
Customers will be notified next week of the violation to satisfy a public disclosure requirement by the Oregon Health Authority.
The contaminant level in the water is not an emergency. The city has to notify customers within 24 hours when there is an emergency.
“I’m still drinking the water,” said Ken Cook, the director of the city’s Public Works Department.
The violation was tied to the construction of the Spur 14 water source from a creek that produces the cleanest water in the Bear Creek watershed, the city’s water supply.
The project was supposed to be completed in October, according to the Public Works Department, but has been pushed back to December.
The city has been using the Main Lake water source during the project, because the Middle Lake source had to be taken offline. Middle Lake typically has the best water in the fall and early winter.
The city used a higher than normal amount of chlorine this fall to treat organic matter in the Main Lake water. The interaction between the chlorine and the organic matter produces what are known as disinfection byproducts, which are contaminants.
In November, the city exceeded the maximum contaminant level for the quarter, readings that pushed an annual average in one category — haloacetic acids 5 — above the threshold for the year. The standard for HAA5 is 0.060 milligrams to liter, and the city was at 0.062 milligrams to liter.
The city is now using Middle Lake water, so public works officials believe disinfection byproduct levels will drop back to acceptable concentrations.
According to a draft of the notification letter, people who drink water in excess of the maximum contaminant level for many years may have an increased risk of cancer.
Customers are urged to share the information with others who drink city water but may not receive the notification letter, such as people in apartments, nursing homes, schools and businesses.