Small amount of water from the Columbia South Shore Well Field will be added to water from the Bull Run Watershed until March 21.

PORTLAND TRIBUNE FILE PHOTO - The dam in the Bull Run Watershed.Beginning on March 12, the Portland Water Bureau will begin blending a small portion of water from its Columbia South Shore Well Field with water from the Bull Run Watershed as part of its annual well field mainteance operation.

The blending will continue until March 21, when the bureau anticipates a return to 100 percent Bull Run water until this summer, when well field water is traditionally added as water below the Bull Run Dam falls low to prevent tubidity.

According to the bureau, the average contribution of groundwater to the system will be approximately 20 percent of the total daily water demand. Due to the low percentage of groundwater being blended with the Bull Run Source, the bureau says it does not expect there to be a noticeable change in water chemistry.

It can take up to two weeks, depending on location and overall water demand, for the blended water to make its way through the distribution system to homes and businesses.

The bureau says the city's groundwater supply is a complex system composed of groundwater wells, pumps, treatment systems, electronic controls, and other equipment that must be operated regularly to identify maintenance needs. By doing this operation routinely, the bureau helps ensure the reliability of the system when needed, either in an emergency or to meet seasonal supply demands.

According to the bureau, the Columbia South Shore Well Field is a high-quality water supply that meets or surpasses all federal and state drinking water regulations. As a result of careful planning, Portland is fortunate to have access to two excellent water sources that allow us to be prepared to meet the range of supply and demand conditions that occur in the Portland water system, the bureau says.

Although public notification is not required, the bureau traditionally informs the media and sensitive water users when it activates groundwater and when it has significant operational changes.

Customers with questions are encouraged to call the Water Line at 503-823-7525.

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