Mayor Denis Law signed an emergency declaration Tuesday that will allow repairs to begin Wednesday of about 200 feet of failing sewerline near the Royal Hills Apartments.

The city has chosen the repair option in which it will dig a trench about 5 to 10 feet deep and replace the concrete pipeline with a plastic one.

The cost is estimated in the $100,000 to $125,000 range, which is less than other repair options, said Gregg Zimmerman, the City of Renton public works administrator.

However, the unbudgeted cost will mean the city will have to delay a project in its wastewater division and use that project’s funding for the repairs. The city is considering which project to delay.

The idea is to start the repairs Wednesday morning and hopefully finish on Friday, Zimmerman said.

The city is feeling a sense of urgency to get the repairs done because of several risks, he said.

Already, two 16-foot sinkholes have formed in Royal Hills Drive, including one that was repaired. The second one is covered by steel plates, covering the width of the road. The city doesn’t want a third hole in the street.

A sinkhole could open in the easement through the apartment complex.

“We don’t want that to happen,” he said. However, given the pipe’s condition, “it’s only a matter of time before we have a failure there.”

The pipeline, buried about 16 to 20 feet, doesn’t run directly under any of the apartment buildings.

It’s also possible that debris could continue to enter the pipeline in the broken spots, collecting in the pipeline where it narrows. That scenario is what occurred when debris clogged the pipeline, forcing sewage from a manhole and down an access road to the Cedar River earlier this month.

The monitoring city crews are doing and temporary repairs are costly, too, he said.

Apartment residents would see equipment, materials and work crews mobilizing in a large yard area and on Royal Hills Drive Wednesday morning.

The city is talking with apartment management about maintaining access to the complex, which is only served by Royal Hills Drive.

The complex is regularly served by Metro buses and by school buses, using Royal Hills Drive. The city has talked with managers about routing buses through the complex, but they expressed concern about the safety of residents, including children, Zimmerman said.

He doesn’t expect any work will occur overnight, but it could go into the evening. Such decisions are made in the field, given the quick timeframe for the work, he said.

The city is pressing to get the work done as soon as possible, Zimmerman said.

“We don’t want this to persist another week,” he said. “We have seen what can happen. We aren’t eager for more incidents.”

An emergency declaration doesn’t require City Council approval, Zimmerman said, but the council is being kept informed. Under the declaration, the city won’t go through a bidding process. However, city officials have “ballbark” estimates and would “ask questions” if a contractor estimate varies greatly from that, he said.

Shoreline Construction, involved in the repair of the initial sinkhole, has given an estimate and another contractor was planning to do so, too, Zimmerman said.

The repair cost is based on time and material, he said.

About 200 feet of sewerline where two sinkholes opened up on Royal Hills Drive “is about shot,” Zimmerman said, after it was inspected by a camera on a wheeled carrier last Friday. The camera inspected the line from the edge of the Tiffany Park neighborhood through roughly the middle of the Royal Hills Apartments.

Last Friday, the city hooked together hoses to carry sewage around the stretch of sewage line it wanted to inspect. The bypass starts in a manhole on Index Avenue in Tiffany Park, goes down a steep hill and then crosses Royal Hills Drive to another manhole in the apartment complex.

The entire bypass is about 250 feet, including the hill section. The pipeline is in better condition on the hill slope and on the downflow side of the manhole in the apartment complex.

The line and pump were left in place in case they need to be pressed into service again. City crews inspected the lines over the weekend and this week.

The camera was carried through the pipeline using a wheeled carrier belonging to a city contractor. The city has its own on back order.

The camera revealed the cause of the second sinkhole: yet another hole in the pipeline.

Aggregate or small rock is exposed in the concrete pipeline, a sign of corrosion, and gaskets are dangling into the line, which slows the sewage flow, according to Zimmerman.