Mercer Island’s second ‘boil water’ advisory was lifted Oct. 8 at noon, but the source of contamination is still unknown.

The first advisory lasted from Sept. 27-29 after the discovery of E. coli in the water system. The bacteria was found again on Oct. 1, prompting a longer advisory and a more cautious and comprehensive approach to lifting it.

Mayor Bruce Bassett said the city recognizes the financial impact of the advisories on Island businesses, and that it will try to publicize a “Dine Local” campaign.

He and city staff met with 30 business owners on Oct. 8.

“It’s been a hard 12 days,” he said at a press briefing. “(Businesses) have been hit hard by this. Some lost part of their normal business, and many were forced to close entirely. They’ve discarded expensive inventory, twice.”

The city provided 2,200 cases of water to vulnerable populations on the Island for a cost of $8,000, said emergency manager Jennifer Franklin.

The rest of the financial impact isn’t yet known, Bassett said, noting that overtime, purchases or rentals of specialized equipment and resources for the Emergency Operation Center (EOC) will factor in.

The city also hired an outside consultant, Confluence WTIC, which will cost $10,000 to $15,000. The hope is that an expert review will help uncover things that may have been missed, and find ways to protect the Island’s water supply in the future. One idea is to install mixing equipment in the reservoirs to maintain stable chlorine residuals.

“Long-term package is getting those mixers in place. Long-term strategy is for the city of Mercer Island to identify if they want to have their own ability to inject chlorine and not have to rely on SPU (Seattle Public Utilities),” said Clark Halvorson, director of the DOH’s Office of Drinking Water.

It’s common to never find the source of contamination, or “smoking gun,” in these situations, said DOH officials. Inspectors visited all active construction sites on the Island and didn’t note any problems.

There were questions about whether an incident at the high school – in which mortar dropped into the sewer line caused a sewage backup – could have been the source of the contamination, but there seems to be no connection, said Terry Smith, utilities operation manager. The school district had its backflow device retested, and it passed.

After inspections of city facilities revealed no abnormalities, crews started looking into cross connections and residential backflow prevention devices. Twenty-four devices were identified as risks, and another few hundred are technically out of compliance, said Maintenance Director Glenn Boettcher.

Derek Pell, a drinking-water engineer for the DOH, said that there are hypotheses about what’s going with the pipes, involving possible corrosion and biofilms – which may form inside drinking water distribution systems similar to how plaque forms on teeth. Biofilms exist even in healthy systems. Pell said Mercer Island’s situation is “new ground” for the DOH, which usually only finds E. coli issues in unchlorinated systems.

“I believe your staff is doing a really great job of trying to find it, but 98 percent of your facilities are buried,” Pell said. “If you can’t find it and fix it, then you need to have a second barrier in place to protect the public health.”

That second barrier is a robust disinfection process. Pell said that the city should have higher chlorine residuals to take on contaminants.

Bassett said that just boosting the chlorine levels could be “masking the problem” if there are issues with cross connections or other aspects of the system.

“It’s more complicated than just saying if we get to a chlorine level of 1.2, problem solved,” he said.

Water Timeline

Sept. 24 – A sample tests positive for E. coli and Total Coliform in the northwest corner of the Island, at sample station MI-3.

Sept. 26 – Four out of eight samples test positive for E. coli and Total Coliform – at a booster station and sample stations MI-4A and MI-5A on the North-end and station MI-1 on the South-end.

Sept. 27 – Sept. 26 results received. First ‘boil water’ advisory issued. One sample tests positive for Total Coliform at MI-4A.

Sept. 28 – Retests of 11 samples show no problems.

Sept. 29 – Schools close for sanitizing. First ‘boil water’ advisory is lifted.

Oct. 1 – One sample tests positive for E. coli and Total Coliform at Station MI-4A. One tests positive for Total Coliform at MI-1.

Oct. 2 – Oct. 1 results received. Second ‘boil water’ advisory issued.

Oct. 3 – Number of samples taken increases threefold (to 18). Crews begin direct injections of chlorine, vault inspections and flushing of water lines. Some restaurants allowed to reopen.

Oct. 4 – Dive teams sent into tanks find no abnormalities.

Oct. 7 – Fifth day in a row with clear test results. Second ‘boil water’ advisory still in effect.

Oct. 8 – Second ‘boil water’ advisory lifted.

Oct. 13 – Samples clear for 11 day in a row.  City launches “Dine Local” campaign.