In this 2010 file photo, Jeff Riner, a water plant operator at the Clinton Water Treatment Plant, stands by one of the plant's treatment tanks.

In June 2012, Lawrence’s water supply took on what city leaders described as an “earthy and musty” taste and odor because of a byproduct of dead algae in the raw water taken from Clinton Lake.

The taste, which was the subject of complaints from residents, lasted about 10 days. The levels of the byproduct, called geosmin, recorded in the city’s water supply were almost four times the amount than had ever been recorded previously.

“It was a very, very unusual event,” said Dave Wagner, the city’s utilities director, to the City Commission in November. “It was a record-setting event for us. We’ve not seen one since, but that doesn’t mean we won’t see another one.”

Nearly four years later, the city is set to make improvements to its water treatment process in an effort to ensure the taste isn’t affected as long — or as powerfully — again.

The improvements come at a cost of approximately $3.9 million. The City Commission agreed Tuesday to award a bid for that amount to Kansas City-based Crossland Heavy Contractors.

Another approximately $1.4 million has already been spent on an evaluation of the treatment process and the design and engineering of the new operations that will be put in place.

Jeanette Klamm, a management analyst with the city’s utilities department, said this “isn’t a health and safety issue.” Even during the event in 2012, residents could safely drink the water.

Other, smaller taste and odor changes happen frequently, she said. Oftentimes, because the city monitors it, the two- to three-day episodes go by unnoticed.

“It’s strictly an aesthetic thing,” Klamm said. “We’ve had taste and odor events over the course of many years. It came to a head with that one very large event.

“The complaints we hear are that it tastes funny or it tastes different. Some people are very sensitive to it, and some people don’t notice it so much… It’s in no way a health and safety risk, it’s really a quality issue.”

The project to introduce new treatment processes is expected to start in February and be completed in about a year. It includes adding to Clinton Water Treatment Plant a new rapid-mix system, which disperses chemicals in the water, and new equipment to inject into and remove from the water a higher dose of carbon powder.

The city’s current treatment system relies on carbon powder to filter the water. It removes about 90 percent of the blue-green algae byproduct.

But Rachel Thompson, an environmental engineer with Burns & McDonnell — the engineering design firm that evaluated the treatment process — said a high level of taste and odor compounds, such as what occurred in the city’s water supply in 2012, “puts a lot of stress on the system.”

The city’s system of using carbon powder is “reaching its limits in what it could achieve,” she told the City Commission in November.

Besides adding the physical infrastructure, the improvements include adding carbon dioxide to the water, which gives the city better control of the pH level of the water, and replacing the liquid lime and ferric systems.

Burns & McDonnell found some improvements were needed to the Kaw River Water Treatment Plant, too, but those will have to be delayed several years because of the lack of available funding.

Both treatment plants provide water to Lawrence, Baldwin City and Douglas County’s rural water districts.

The engineering design firm estimated improvements to the Kaw plant would cost approximately $2.6 million.

The firm estimated the project at the Clinton plant would cost approximately $4.8 million. Bids ranged from Crossland’s, at $3,879,000, up to $4.7 million.

The funding for the approved project is coming from a city capital improvement program and the utilities department’s rate plan from 2013 through 2017.

The improvements aren’t a guarantee that the taste and odor of the city’s water supply won’t change, said Andy Ensz, a project engineer with the utilities department.

“We can’t guarantee that it will completely eliminate all of it,” Ensz said. “But the event in June of 2012 was really, really high and really unusual. This would certainly help on smaller events and it would help to a substantial amount in larger events.”

City staff is calling the improvements “phase one.”

Burns & McDonnell identified that what could be needed is advanced oxidation practices, such as adding ozone, which can eliminate byproducts without adding chemicals to the water.

But the equipment is expensive. Shortly after the June 2012 incident, city staff roughly estimated that the cost to install the equipment at both treatment plants would be $18.5 million.

Klamm said after the first phase of improvements are complete next year, it will take a few more years to determine if phase two — the advanced oxidation — is necessary.

“This part had to be done either way, so what we decided was to do the optimization, add the extra chemicals and do everything that’s involved with this particular project, and then sit back and evaluate,” Klamm said. “It’s going to take a few years because you can’t just turn it on and see if it works. You have to wait and see how everything reacts.”