COEUR d'ALENE - Coeur d'Alene wastewater crews responded to a sinkhole on Tuesday between 16th and 17th streets on Mullan Avenue.

Rick Shoner, a heavy-equipment operator for the department, said they were not exactly sure what caused the sinkhole to develop, but guessed it was probably the sewer lines settling under the road.

Shoner said a lot of the sewer work in the old neighborhood was done years ago without heavy equipment, and sometime the soils did not get compacted to enough to prevent settling.

"When you have 10 feet of soil settling on the pipes it just kind of pulls things apart," he said, explaining that the soils then begin to wash away down the sewer line, and eventually a sinkhole forms.

Shoner believes it occurred in an area where there was a drop sewer main installed years before. He said there was an 8-foot-deep line dropping into a 10-foot-deep line, and if that broke, it was the likely cause.

When workers dug up the sewer lines, they also found an old wooden water line that could have caused the problem as well.

Nevertheless, Shoner said the crew planned to replace a section of the sewer main and fix other issues with a manhole in the area before they covered it up and opened Mullan to traffic again.

That work should be completed sometime today.