A City of Renton crew will inspect a roughly quarter-mile section of a 20-inch sewerline with a camera early Friday morning starting in Tiffany Park to determine whether it is damaged.
The inspection comes after a second sinkhole opened up in Royal Hills Drive next to one city crews finished filling last Friday.
That first sinkhole revealed a corroded section of the pipeline that was the entry spot for debris that clogged the sewerline near where it narrows to 14 inches, forcing sewage to gush out of a manhole. Some of that sewage made it to the Cedar River down an access road.
Regular inspections by the city have found no plugs in the pipeline or overflows from that manhole.
The city has had a sense of urgency to inspect the pipeline’s interior for damage or breaks.
The city was waiting for the delivery of a heavy-duty, wheeled carrier it purchased for the camera before it began the inspection. Now, with the emergence of the second sinkhole, the city is using a carrier from a contractor.
Before it can inspect the sewerline, the city will divert the sewage it carries in linked hoses using pumps for roughly 1,000 feet from Tiffany Park, down the hill and finally to the far side of the Royal Hills Apartments on Royal Hills Drive, said Gregg Zimmerman, the city’s public-works director.
The pipeline carries about 800 gallons of sewage a minute.
“I think we can do this without any interruption of sewer service,” said Zimmerman, of the inspection and any repairs that are required.
The camera inspection should take most of the morning. The pumps are quiet, Zimmerman said.
The city has closed and barricaded the north side of Royal Hills Drive at the sinkhole, limiting traffic to just one lane. Shoreline Construction, which assisted in the repairs to the first sinkhole, brought in 20-foot-wide steel plates to place along the entire width of the street.
The second sinkhole is right next to the one that appeared on in the roadway on June 3. The corroded pipeline was repaired and the hole filled by early morning on June 4.
The second sinkhole opened up late Wednesday. It was filled with a granular material before it was covered with the plates, Zimmerman said.
Zimmerman wants to gather information from the interior inspection of the pipeline first so that the city doesn’t end up doing a series of repairs that are thrown out when a final solution is reached.
“Once we have the information, we will try to do a repair that makes the most sense,” he said. “We want to fix the stretches that have collapsed and are in a failing condition.”
The camera inspection will include the stretch of pipeline that runs in an easement through the Royal Hills Apartments. The pipeline is about 16 feet under the surface, based on the depth of the sinkhole.
“We don’t want to see any sinkholes in the easement that are close to the apartments,” Zimmerman said. What’s encouraging, he said, is that the sinkholes have appeared in the street, rather than on the apartment grounds.
The city has held brief talks with the apartment management about routing Metro or school buses through the complex if necessary to avoid repairs, he said.
