Salem officials are planning to spend more than $75 million on construction to beef up defenses against toxic algae as they attempt to avoid a rerun of last year's drinking water crisis.

Salem's water, pulled from the North Santiam River, became so contaminated by algae blooms upriver in Detroit Lake last May that city officials were forced to warn parents of young children and medically vulnerable adults not to drink from the tap.

The public health emergency then escalated into a public relations nightmare when people learned city officials hadn't told them about the contamination until days after it was detected.

This year, the best-case scenario is that Salem's drinking water goes untainted by toxins through the spring and summer.

Worst case: City officials have to issue a do-not-drink warning for all residents, triggering runs on bottled water and the return of drinking water stations.

This year should be different.

If toxins become a problem, officials will treat the water with powder activated carbon and additional chlorine — a big change from the start of the water crisis last year.

The new treatments have been added to the existing sand filtration system that has cleaned Salem's water in the past.

"The algae and the toxins can show up at any time," said Salem Public Works Director Peter Fernandez. City officials have worked over the winter to prepare for this year and the next, he said.

To prepare, residents should stock up on at least two weeks' worth of bottled water, much like state officials have recommended for a massive earthquake or tsunami.

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For the long term, city officials are buying an approximately $40 million ozone treatment system to be finished in 2021.

"Ozone is a powerful oxidizer that removes contaminants from the water," Fernandez said. "Essentially, it works the same as adding chlorine to the water at the end of our treatment process."

Ozone is a lot stronger than chlorine, said city spokeswoman Heather Dimke.

Officials also are spearheading a pilot project with Oregon State University researchers for an early warning system that uses machine learning to predict when toxins may be present. That system will be tested this year but not folded into formal response plans.

Here's the estimated construction cost breakdown for added safeguards, according to a list supplied by the City of Salem:

$40 million: Geren Island water plant's ozone treatment system

Geren Island water plant's ozone treatment system $3.5 million: Short-term Geren Island projects to improve water treatment

Short-term Geren Island projects to improve water treatment $15.7 million: Flood berms, groundwater wells and additional controls at Geren Island

Flood berms, groundwater wells and additional controls at Geren Island $11.5 million: Improvements for aquifer storage and recovery wells

Improvements for aquifer storage and recovery wells $4.5 million: Groundwater storage wells inside Salem

"A portion of the funding is already in place and the remaining funds are programmed in the 5-year Capital Improvement Plan that is recommended for council approval in June," Dimke said.

Meanwhile, the Oregon Health Authority has adopted regulations for monitoring cyanotoxins and issuing do-not-drink advisories across the state. For example, water must be tested for the toxins at least every two weeks from May 1 through Oct. 31.

Officials don't expect residents to experience adverse health effects if they drink water with cyanotoxin concentrations at or below health advisory levels for up to 10 days, according to the OHA.

Cyanotoxins may cause a range of health problems for people who are exposed, including kidney and liver damage, according to the U.S. Environmental Protection Agency.

Rising global temperatures and nutrient-rich environments are predicted to make microalgal blooms occur more frequently and last longer, according to a 2017 report from the University of Texas at Austin.

"Cyanobacteria traditionally like warmer temperatures," said Dr. Schonna Manning, one of the report's authors. "It's a real simple temperature relationship."

"I think it will become more of a problem for municipalities, especially water treatment systems," said Manning, who is a research assistant professor at the university's Department of Molecular Biosciences.

For Salem, the problem isn't likely to go away.

"You can think what you want about climate change," Fernandez said. "The fact of the matter is, the water's warmer."

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With the ozone treatment system still two years out, city officials will bombard the water with treatments on all sides in an attempt to remove toxins if they appear in the water at concerning levels between now and spring 2021.

Construction of these short-term efforts at the Geren Island Water Treatment Facility cost $3.5 million, according to city figures. That includes widening the channel, improving flow monitoring and adding sand to the roughing filter.

Powder activated carbon, sand filtration and chlorine are the main weapons that toxins must face en route to Salem faucets.

To prepare the water system's roughing filter this year, officials added about 4,500 cubic yards (a dump truck usually holds some 10 to 12 cubic yards) of new sand, said City Engineer Brian Martin.

"The roughing filter is the pond that we use to remove sediment from the water before we send it to one of the other filters," Fernandez said. "We do this to provide an extra level of treatment — pre-treatment — to the water."

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Also in the lineup is powder activated carbon. City officials last year introduced powder activated carbon to rapidly remove toxins from the drinking water. However, getting the carbon to settle in the water before it moved on to the roughing filter proved a challenge.

If the carbon doesn't settle properly, it clogs the roughing filter and then officials can't get water out quickly enough, Fernandez said.

So officials widened the basin where the water sits, increasing the time it has to settle from one hour to two.

City officials plan to set aside $40,000 for powder activated carbon in next fiscal year's operations budget. They issued a $2 million purchase order to their supplier in case more is needed in the next few years, Fernandez said.

"We have a lot of PAC stored at Geren Island, and we can purchase more if we need more," he said.

Further bolstering the defense is the addition of acetic acid.

"The slow sand filter treatment process relies on nature to do the work for us," Fernandez said. The slow sand filtration process uses what's called a "schmutzdecke" with living organisms.

"Acetic acid — a form of vinegar — provides nutrition for the organisms in the schmutzdecke," Fernandez said. "What we found last year is that by adding acetic acid to the water entering the slow sand filter, the organisms were better able to digest the toxins."

The last step is chlorinating the water. Martin said research has shown higher dosages of chlorine can remove algal toxins. Still, they would remove excess chlorine before it gets to water users.

They would add more at the plant, then the water has about eight to 10 miles to travel before it's removed, Martin said. Officials have added a site to reduce chlorine levels back to normal, he said.

"They are three treatment options that can be used individually or in combination," Martin said. "We are currently using the roughing filter and will continue to do so throughout the summer."

"If surface water conditions change and we start seeing toxins then we will start increasing chlorine levels in small increments," he said. "If the toxin levels continue to climb then we will introduce the PAC."

Throughout all this, officials would be monitoring the water at various points on its run from Detroit Lake down the North Santiam River to the water distribution system.

"After it's run this gauntlet, do we still see any toxins at the very end? If we do ... then we have operational plans for alerting the public," Fernandez said.

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Salem officials were raked over the coals last year for their poor communications in the early days of the water crisis.

City officials, on the advice of OHA, decided not to immediately tell the public about toxins discovered in the water. On May 29, the city issued a do-not-drink advisory for children younger than 6 years old and medically vulnerable, including dialysis patients and nursing mothers.

Oregon's Office of Emergency Management compounded communications problems when it mistakenly sent an emergency alert on May 29 to Oregonians up and down the Willamette Valley warning of "civil emergency" and telling them to "prepare for action."

At the start of the water crisis last year, state rules didn't regulate when city officials had to issue a no-drink warning for cyanotoxins.

At key component of OHA's new rules is that after a sample shows toxins above health advisory levels, officials must take a confirmation sample to double-check "as soon as practical, but no later than 24 hours after receiving results."

If the cyanotoxin concentration still exceeds health advisory levels, officials have to issue a health advisory notice as soon as they can saying the water isn't safe to drink, but no later than 24 hours after they get confirmation results back.

Advisories must state, "Consuming water containing concentrations of cyanotoxins over the health advisory level for more than 10 days may result in upset stomach, diarrhea, vomiting, as well as liver or kidney damage. Seek medical attention if you or your family members experience illness."

Whether the do-not-drink advisory would be for the whole population or just vulnerable residents would depend on how concentrated the toxins were.

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This year, if the steady barrage of water treatments isn't enough to stop toxins from getting through to the final point before the city's water distribution system, city officials are prepared to issue another do-not-drink advisory and activate drinking water stations.

"We're hopeful that that's not going to happen this year," Dimke said. "We certainly can't rule that out by any means — so we're watching it very closely."

"We learned a lot last year," Fernandez said. The city has three water distribution trailers, they're getting bladders to fill with water and their tankers have been refurbished, he said.

Would Salem residents see National Guard trucks rolling down streets to deliver water again? Not for a do-not-drink advisory limited to vulnerable populations, according to Fernandez. "We're ready for that one."

But, "God forbid," if a full no-drink advisory were issued for everyone in the city, "we would need help, because then what we really are talking about is going from like eight distribution centers to 18," Fernandez said.

Jonathan Bach has been a business and City Hall reporter with the Statesman Journal since 2016. To support his work, Subscribe to the Statesman Journal. Contact him by email at jbach@statesmanjournal.com, call (503) 399-6714 or follow him on Twitter @jonathanmbach.

Here's the treatment sequence if officials use all their options at once, according to City Engineer Brian Martin: