Portland may have to build an expensive treatment plant at the Bull Run reservoir to treat a potentially-deadly parasite after the Oregon Health Authority revoked the variance that prevented construction on May 19.

In a letter announcing the revocation to Portland Water Bureau Administrator Michael Stuhr, OHA Administrator Jere High said the city must establish a compliance schedule and interim control measures to prevent the spread of Cryptosporidium by Aug. 11, 2017. The City Council is expected to discuss its option at a June 27 work session.

The revocation of the variance followed a March 8 letter from the water bureau to OHA saying it could no longer meet the terms of the variance, which had been granted in 2011 because water from the Bull Run watershed — the city's primary source of drinking water — had historically been so clean.

But periodic testing required by the variance began detecting small amounts of crypto — as the parasite is commonly called — in January 2017, increasing the amount of water that must be tested. By the time the final positive sample drawn on March 12, the water bureau had exceeded its allowable level for the test period.

"Even if we detect no more crypto for the remainder of the demonstration monitoring period, we would not be able to meet the threshold for retaining the variance," says bureau spokesperson Jamie Cuti.

Crypto is transmitted through animal feces. It can cause cryptosporidiosis, a respiratory and gastrointestinal illness, which killed 104 people and sickened thousands of others in 1993 in Milwaukie, Wisconsin. That outbreak prompted the EPA to adopt a rule requiring all municipal water systems to treat for crypto. Portland was the exception until May 19.

In 2009, it estimated that a treatment plant that used ultraviolet light would cost $100 million. A filtration plant that could treat additional contaminants was estimated at $385 million. Water rates might have to be raised to pay for either option. Such an increase would be paid by both city and suburban wholesale customers.

You can read a previous Portland Tribune story on the issue at tinyurl.com/mvqgdqp.