Few answers in sewage plant inquiry

The cause of a fatal Spokane sewer plant accident on May 10 may be traced to a series of problems rather than one single factor, a top city official said Thursday.

Preliminary findings from an independent investigation are not expected until September. Results of a separate state Department of Labor and Industries probe may not be known until November, officials said.

“I think we will find in the end it was a variety of things that led up to the incident happening,” said Roger Flint, Spokane’s city director of Public Works and Utilities.

Flint confirmed reports, backed up by public records, that show the plant was having problems processing sewage sludge in the weeks leading up to the accident. However, he said, staff members believed they had solved those problems before the accident.

City officials held a press briefing on Thursday and released additional records showing that methane gas pressures and sludge levels inside the plant’s three “digester” tanks fluctuated markedly in the five hours preceding the accident.

Maintenance mechanic Mike Cmos Jr. was killed when a buildup of pressure in digester tank No. 3 led to an explosion that ripped the lid, or roof, from its walls. The roof fell down into more than 2 million gallons of sludge, a small portion of which drained into the Spokane River. Two workers were seriously injured.

Cmos and the others were at the digester trying to prevent sludge coming out of roof vents from going into the Spokane River.

Flint and the plant’s lead operator cautioned that fluctuations shown by metering data do not necessarily point to a cause of the accident. Workers had attempted to prevent tank No. 3 from overflowing by reversing inflow about 2 p.m., about an hour before the roof broke free.

Earlier in the day, the early morning operator had started transferring sludge from digester No. 2 to digester No. 3 in an effort to get digesters operating at optimum levels. The sludge transfers were considered routine.

For some reason, sludge levels in tank No. 3 continued to increase even after inflow was stopped, officials said. Investigators have been asked to come up with answers about how that happened.

Flint said the investigation was slowed by safety concerns and efforts to coordinate information-gathering among the several parties involved in the probe.

Nadine Grady, industrial hygiene compliance supervisor for the Washington Department of Labor and Industries, said her agency has six months to complete its investigation and may well need the full six months to issue its findings.

Experts from a nationally recognized forensic engineering firm have gathered documents, photographs, measurements, witness statements, tank samples and other evidence in their effort to piece together what happened. Exponent Failure Analysis Associates of Menlo Park, Calif., was hired by the city in early June on a no-bid contract worth at least $200,000.

In addition, a Mayor’s Oversight Committee of community members is reviewing the investigation, and an in-house committee at City Hall is also looking at the accident.

Robert Goebel General Contractors of Spokane was hired by the city in June on a $225,000 contract to clean the damaged tank and remove debris.

On Thursday, the Goebel crew and a crane subcontractor were nearly finished removing the damaged domelike roof at the bottom of the tank. Over the past two weeks, they used a crane and jackhammers to break the roof into pieces so it could be hoisted out of the mammoth tank. Nearly 150 tons were removed, Flint said.

Some crew members were using shovels and a hose to clean up smaller pieces of sludge-coated debris left at the center of the cone-shaped tank bottom. Shovelfuls were being dumped into a large skip box to be hoisted out of the tank.

A city-owned vacuum truck was also being used to remove pebble-sized pieces of debris.

Deputy Mayor Jack Lynch commended workers and contractor employees at the plant for performing well under difficult conditions in the past 11 weeks. “Thank you. You are doing a great job,” he said.

Lynch promised an open and thorough investigation of the accident to ensure nothing like it ever happens again.

Dating back at least two years, the plant has been undergoing extensive upgrades, including the planned addition of a fourth digester tank at the west end of the complex adjacent to Riverside State Park in northwest Spokane.

Flint said the city plans to speed up construction of the additional digester to have it completed as soon as possible, in about two years. It had been planned for completion in about 10 years, he said.

In the meantime, the city is awaiting Exponent’s structural analysis on the damaged tank to determine whether it can be salvaged and reused, Flint said. This winter, the city hopes to use the damaged vessel to store processed sludge during the months it is not possible to dispose of sludge “biosolids” by spreading them on farm fields.

“We’re limping through operations on two digesters now,” Flint said.