Portions of Beaverton and Tigard receive drinking water from Bull Run.

PORTLAND TRIBUNE FILE PHOTO - Portland has switched its water source from the Bull Run reservoir to groundwater wells along the Columbia River.The Portland Water Bureau switched its source of water to wells along the Columbia River on Monday after repeatedly finding a potentially deadly parasite in the Bull Run reservoir, the primary water source for the city and much of the surrounding region.

The Tualatin Valley Water District gets its water from Bull Run. The district serves a portion of Beaverton and a portion of Tigard — most of it west of Highway 217. The rest of Tigard, King City, Durham and Bull Mountain get water from the Lake Oswego-Tigard Water Partnership, which pulls water from the Clackamas River.

"The recently upgraded filtration system at our water treatment plant removes cryptosporidium and pathogens that may be detected in the Clackamas River water supply," the Lake Oswego-Tigard partnership said Monday. "Ozone, a powerful oxidant, also provides an additional treatment barrier to protect public health."

The parasite found in the Bull Run water is cryptosporidium. It has been found six times in the reservoir since the beginning of the year. The most recently announced findings were in samples tested on Tuesday, Feb. 7, and Wednesday, Feb. 8.

The Portland Water Bureau has not yet decided how long it will rely on the groundwater wells.

"Our process for making that decision is to continue to sample the Bull Run for cryptosporidium and gather information about these detections. With additional information, and in consultation with public health officials, the bureau will decide when to re-activate the Bull Run supply," said bureau spokeswoman Jaymee Cuti.

Although bureau officials continue to insist Bull Run water is safe, they say they are making the switch out of "abundance of caution."

Beginning Monday, 100 percent of Portland's water will be coming from the Columbia South Shore Well Field. It is normally used as a second source of water in the summer months after the reservoir is drawn down to reduce turbidity.

According to the Portland Water Bureau, it may take up to two weeks, depending on location, for groundwater to make its way through the distribution system to homes and businesses. The bureau also sells water to other cities and water districts in the region.

"The recent detections do not pose an increased health risk. After a series of very low level detections, we are proactively activating our secondary source while we collect more data," bureau administrator Michael Stuhr said Monday. "The city continues to be in compliance with the treatment variance issued by the Oregon Health Authority."

The U.S. Environmental Protection Agency has required cities with open water sources like Portland to treat for crypto, as the parasite is commonly called. Portland was granted a variance by the Oregon Health Authority in 2012 because water in the reservoir has historically been so clean. It requires the bureau to routinely test samples of water for crypto. None was detected until a sample drawn on Jan. 2 was tested. The other samples that tested positive were drawn on Jan. 3, 25 and Feb. 1.

Although it is too soon to predict what will happen, the Oregon Health Authority has the power to require the PWB to build a treatment plant at the reservoir to kill the potentially dangerous parasite.

That is because crypto can cause cryptosporidiosis, a respiratory and gastrointestinal illness. It can affect anyone, but is especially dangerous for people with weakened immune systems. An outbreak killed 104 people and sickened around 400,000 others in Milwaukee, Wisc., in 1993, helping to prompt the EPA to adopt its treatment requirement.

The parasite is spread through animal feces. Because there are no domesticated animals in the Bull Run watershed, city Water Quality Team Manager Yone Akagi said wild animals most likely are the source of parasite found in the reservoir samples.

Akagi does not know why the parasite has suddenly been detected in the reservoir. One possibility is the heavy storms that have hit the region this year, Akagi said. They may have washed more contaminated soil than usual into the reservoir.

Whatever the cause, the positive results already have required the Water Bureau to accelerate its monitoring schedule, increasing the amount of water collected and tested from 50 liters twice per week to 250 liters four times per week. It can be argued that the more-frequent and larger collections are theoretically increasing the chances that more crypto will be found in the samples.

According to Oregon Health Authority spokesman Tony Andersen, the state agency is allowing the Portland Water Bureau to continue collecting and testing Bull Run water for crypto. But Andersen says the health authority also is "working through a range of options for the future" in case the results exceed the allowable limit.

That limit is 0.075 or more "oocysts" per thousand liters of tested water at the conclusion of current one-year monitoring period at the end of the year. An oocsyst is a miscroscopic structure that proves the existence of the parasite.

If that limit is exceeded, OHA will revoke the variance and set a schedule for the the water bureau to install the EPA-required treatment.

The last time the bureau studied building an ultraviolent treatment plant to kill crypto in the reservoir was in 2012, when the cost was estimated at $70 million. The cost would be paid by PWB ratepayers, as with the recent cost to disconnect the open reservoirs at Mount Tabor and Washington parks. That was done to meet EPA requirments to keep crypto, other microogranisms, viruses, and other contaminants out of public water supply systems.

Anyone with questions can call the water line at 503-823-7525.