Some Oahu residents may be to blame for some of the sewage spills after heavy rains, city officials said.
Now city workers are trying to smoke out the culprits.
City workers attached a smoke blower to a manhole on Kalali Street in Kaneohe to find leaks.
"We're out here in the rain looking for the obvious. Rain gutters tying into our sewer lines. This is not a compliant system. Sewer is sewer. Storm water is storm water," said Clement Padeken of the city's Environmental Services Department.
When too much rainwater gets into the sewers the city is forced to release untreated water into the ocean and close surrounding beaches, officials said.
"It taxes the system. It overwhelms it. The system is not designed for heavy rain water," Padeken said.
Officials have noticed a spike in the Kaneohe and Wahiawa areas' sewer systems during heavy rains.
The blower pipes the smoke in and everyone watches to see where it ends up.
If it climbs out of vent out a home's roof, it is working properly, city officials said.
"If it comes out of your rain gutter, or if you have a floor drain exposed to the weather, then we have concerns about that," Padeken said.
At one home, smoke seeped out of the ground in a yard.
The sewer line cleanout cap, that every home has, was cracked. The city crew went ahead and replaced it.
There was a home with smoke coming up along a wall. Padeken said it could be a broken pipe or done intentionally.
On top of connecting rain gutters straight to the sewer lines, he said some residents actually remove or drill holes into the cleanout caps to drain water.
"We know it's happening. It's just a matter of time before we find it," Padeken said. "We don't like seeing a spill entering our oceans."