The city's water utility director, David Warren, abruptly resigned earlier this week.
"After 39 years of public service, it's time for me to give it a rest," Warren said Wednesday.
He didn't cite any other reason and said that he plans to examine other opportunities.
"All I can tell you is I've retired," he said.
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City Manager Robert Layton declined to respond to questions or identify an interim director until a 1 p.m. news conference today.
Warren has been the city's water utility director since 1989, and he oversees some of the city's most expensive and important projects.
The most prominent is the $400 million Equus Beds Aquifer Storage and Recovery Project — or ASR — that has led to continuous water rate increases in recent years and projected hikes for the foreseeable future.
The ASR project takes excess flows from the Little Arkansas River, treats the water and pumps it back into the aquifer.
Warren's departure comes just as the second phase of that project is under construction.
Council member Janet Miller said Warren's exit came as a surprise, and she declined to speculate on why he's leaving.
"My experience working with Dave is that he was an extraordinary professional and, as far as I know, has done a great job leading the water utility," she said.
Other council members either couldn't be reached or declined comment.
Warren has not been subject to any significant public criticism in City Hall. But he did face hard questions from council members in July when he recommended an emergency $2 increase to the base charge on water bills.
The increase was needed, he and others said, because rainy weather had led to less water usage, which meant the utility had less cash to pay off debt on major projects.
Without action, the city could face a bond rating downgrade that would drastically increase borrowing rates, Warren and others said.
Some council members voiced frustrations about the constant increases, especially considering the economic woes so many people face.
But Warren stood by the increase and his department, saying that the ASR project is critical to the city's future and that he had never said he wouldn't need another rate increase to fund the project.
Council members later approved the $2 increase and a 5 percent increase in the price per 1,000 gallons.
Warren said Wednesday he is proud of his work with the city.
Among highlights are the modernization of water treatment facilities, 75 percent fewer leaks than when he started, increased pumping capacity and a project that drastically improved the taste and smell of city water.
"I'd like to take credit for all of that," he said. "But without the great staff the city has... this stuff doesn't happen."
Warren also is leaving his role as board member of the Equus Beds Groundwater Management District 2.
Tim Boese, manager of the district, said that Warren informed board members he was retiring at their meeting Tuesday.
"It's a surprise to us, and certainly he's going to be missed by our board," he said.
Warren's salary for 2008 was $146,973.90, not including benefits, according to public records.
City officials didn't respond to questions about what benefits or severance Warren may get.
Warren also is commander of the Sedgwick County Sheriff Office's Reserve Bureau, where he earned $14,401 in 2008, according to county records.
He said he plans to continue working with the Sheriff's Office.