It’s been 16 months since the discovery of an E. coli contamination in Mercer Island’s water, and a cause has yet to be found. But the city says it has taken positive steps to address some, if not all, of the potential contamination sources since issuing two boil water advisories in September 2014.

The city contracted with Confluence Engineering Group to help with the E. coli response and conduct a long-term action plan, which the Washington State Department of Health (DOH) suggested.

There are “a few more things on the to do list” that should be accomplished within the next six months, said Confluence’s Melinda Friedman. In this transitional stage, Mercer Island has been required to maintain higher than normal chlorine residual levels of 0.6 milligrams per liter.

But the city has progressed in a few key areas, including improving water quality monitoring and ensuring compliance with its cross connection control program. Unprotected cross connections can be an issue if, for example, a residential water main breaks and a contaminant is sucked into the city’s water supply. The city has an ordinance, which was recently updated, to ensure backflow prevention assemblies are installed and tested annually.

The lead maintenance employees in charge during the boil water event, Maintenance Director Glenn Boettcher and Utilities Operations Manager Terry Smith, have since left the city. The city expects to hire a contract employee to focus on water quality monitoring and cross connection control program compliance.

Monitoring has nearly tripled, said current Maintenance Director Jason Kintner. Utility and water rates were raised after the boil water event to provide a funding stream of $550,000 per year for water projects.

“The dollars we spent were worth it,” he said. “We understand our distribution system so much better.”

Finance Director Chip Corder said the money could be spent on the installation of a chlorine injection system, installation of flushing and monitoring stations, increasing the water maintenance level of service or increasing the water main replacement program. Pipes in Mercer Island’s “aging distribution system” are 50 years old in places.

Confluence is using Mercer Island as a pilot project for a new chlorine flushing program. It is “unidirectional” and “high velocity,” “designed to use water velocities to scour the interior walls of water mains and remove the deposit of solids and biofilm,” which can build in older pipes. Utility crews completed the first phase of the pilot program just before Thanksgiving.

Another positive outcome of the E. coli event is the regional collaboration that ensued, Kintner said. City crews are also learning more about Seattle Public Utilities’ system and its limitations, and DOH is recommending new requirements for wholesale water providers based on Mercer Island’s experiences.