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EPA didn't regulate cryptosporidiumlevels until 2006, but findings were reported.

COURTESY PORTLAND WATER BUREAU - Black-tailed deer are among the animals in the Bull Run Watershed whose scat has tested positive for cryptosporidium.Portland Water Bureau officials say they are puzzled why a potential disease-causing microorganism known as cryptosporidium has been found in Bull Run Reservoir water at least 27 times this year.

But it shouldn't be all that surprising considering that "crypto" previously was found in Bull Run water 45 times between March 1999 and November 2002, although not covered by the press at the time.

Those earlier findings did not trigger any state or federal reactions, because the U.S. Environmental Protection Agency didn't regulate crypto until 2006. The Portland Water Bureau included the findings in the annual Water Quality Reports it mails to all customers, though it was not required to do so at the time.

"The EPA was writing its rules during that time, but did not publish them for public comment until 2003," explained Edward Campbell, the Water Bureau's director of resource protection and planning.

By 2012, the Oregon Health Authority thought Bull Run water was so clean that it was considering whether to grant the city a variance from EPA rules that require open public water sources to be treated for crypto.

The parasite had been detected in the water in December 2011 and January 2012. The first sample was taken from the intake site and the second from a tributary. The new findings prompted the health authority to reopen the public comment period on the variance from Jan. 25 to Feb. 8, 2012.

In the end, most commenters supported the variance, in large part because the strains of crypto in the Bull Run Watershed are not likely to harm humans. Although crypto is found in the scat of many animals, the strains most likely to harm humans are carried by livestock and other humans, both of which are barred from the watershed, except for a small number of Water Bureau employees and authorized visitors.

In part, because so little crypto had been found in the Bull Run water after the EPA regulations took effect, the OHA granted the variance in April 2012. Among other things, it required the Water Bureau to test for the parasite — both in the water and in animal scat in the watershed — and to publicly announce any positive findings.

After the variance was granted, crypto was not found in Bull Run water until it was detected in a sample drawn on Jan. 2, 2017. Then it was found in 11 more samples drawn though March 12, prompting the health authority to announce it was revoking the variance, effective Sept. 22. After that, crypto was not found again until a Sept. 24 sample. Then it was detected in 12 more samples. The most recent finding, as of presstime, was on Nov. 8.

But crypto repeatedly was found in the watershed that surrounds the reservoir after the variance was granted. The required scat tests have found crypto in every animal whose scat is on the study list. The positive finding rates vary greatly between all of the other animals by year, with the highest being 67 percent for cougars in 2016.

A strain of crypto potentially harmful to humans — C. parvum — has only been detected three times in scat samples collected in the watershed. All three of the positive findings occurred in 2016. It has not been detected in the water.

The timing of the positive samples found in the water strongly suggests crypto is being flushed into the water supply by heavy rains. However, Water Bureau officials do not know why this did not occur more often over the past 15 years.

One possibility is that the percentage of crypto found in animal scat in the watershed has increased over time. According to the results of tests required by the variance, positive findings have steadily increased from 12 percent in 2014 to 21 percent in 2017.

But the scat collection method is opportunistic. which samples samples found near a road or other convenient location, compared to being collected systematically on a grid. Because of that, the test results may not accurately measure the percentage of animals with crypto every year. (A previous Portland Tribune story incorrectly said the percentages had gone up and down over the year instead of continuously increased.)

Despite the ongoing increase in positive findings, the Water Bureau and Multnomah County Health officials continue to say Bull Run water is safe to drink. Not only are the crypto strains in the watershed unlikely to harm humans, but the amount of crypto detected in each positive finding is very low. Those with compromised immune systems are advised to consult their doctors, however.

And the city has the option of switching to the emergency groundwater wells along the Columbia River, where crypto is naturally filtered out of the water.

After the health authority announced it was revoking the variance, the City Council voted to approve a long-term fix: construction of a filtration plant. That could cost up to $500 million and take 10 years to complete.

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