The city is about to take a $5.6 million loan from the state so it can send waste created during its water treatment process to the Wastewater Treatment Plant.

Like most water systems, the city of Lawrence uses lime to treat water used by its residents. The lime makes the water less acidic, which makes it easier on pipes, and it forms a thin protective coating that acts as a barrier between the pipes and the water.

But the lime also leaves behind a residue that the city must somehow discard.

The city is considered building three lagoons at the Kaw River Water Treatment Plant to serve as a holding site for the “residuals.” Officials said it would be cheaper, however, to pump the residuals across town to the Wastewater Treatment Plant.

“The concept of providing both water and wastewater solids disposal ‘under the same roof’ will be the most efficient in our labor costs,” Michael Tubbs, a city management analyst, said in a memorandum on the subject.

So, the city will build a 12-inch line to carry the residuals 14,000 feet across town between the plants. The loan would be provided by the federal government through the Kansas Department of Health and Environment.

Assistant City Manager Dave Corliss said the city would repay the loan over 20 years at a 3.79 percent interest rate. With interest, the city will pay the state $8.3 million starting in 2004.

The Lawrence City Commission is expected to approve the loan agreement at its meeting at 6:35 p.m. Tuesday at City Hall, Sixth and Massachusetts streets.