A design that violated code and multiple construction problems—including structural deficiencies flagged earlier—caused the sudden collapse of a massive wall at a New York sewage plant in May, according to a forensic engineering report.
Worse, the same deficiencies may extend to other areas of the plant, where continuing safety concerns have led to partial shutdowns and work stoppages.
The collapse at the Binghamton-Johnson City Joint Sewage Plant on May 16 released 580,000 gallons of sludge into a nearby creek, a tributary of the Susquehanna River. Local officials said drinking water was not affected.
The wall section—100 feet long and 23 feet high—held back about 154,000 gallons of treatment materials in four concrete treatment cells. The wall had been built in 2005 as part of a $67 million project to improve the plant’s secondary treatment system.
|The wall collapse at the Binghamton-Johnson City Joint Sewage Plant released nearly 600,000 gallons of sludge into a Susquehanna River tributary.|
The plant’s insurance carrier, Glatfelter Claims Management Inc., of York, PA, has refused to cover the loss, citing faulty design and workmanship.
In denying the claim, the insurer cited an engineering evaluation it had requested from EFI Global, a Massachusetts-based engineering firm. The company provided a copy of EFI’s report to the towns of Binghamton and Johnson City, which own the plant.
The engineering report was obtained this week by the Binghamton Press & Sun-Bulletin, which detailed the findings in two articles.
Lap Splices Cited
“Based on observations made during the examination, the cause and origin of the collapse appears to be a combination of a design that did not comply to code and modifications made during construction of the facility that further reduced the strength of the wall,” Edgar Eslinger, a structural engineer with EFI Global, wrote in the report.
The failure originated at improperly arranged “lap splices,” where metal reinforcement bars within the wall’s 18-inch-thick concrete overlap.
“The point of origin of the wall failure appears to be the lack of adequate development length and/or bond at the lap splice of the main reinforcing on the inside face of the wall,” the report said.
Not only that, the report said, but vertical reinforcement bars should have had splices 104 inches long to meet American Concrete Institute building code requirements. Instead, construction documents called for 81-inch splices—and EFI measured the actual splices at only 64 inches the day after the collapse, the newspaper reported.
The report also found:
• Modifications were made during construction—including wall intersection reinforcements and waterstops—that did not conform to the original construction documents.
• The most notable design departure was installing the splices at the base of the wall, rather than the higher elevation called for in construction documents.
• The wall was designed and built without expansion or contraction joints, which may have caused or aggravated cracking of the wall.
• Deflections and cracking should have alerted the plant’s owners and design team to problems with the wall.
Engineers tested 22 core concrete samples and ruled out material problems and weather as factors in the collapse.
The report noted that several diagonal cracks appeared to have been leaking before the wall failed, and steel angles had been attached to the top of the failed wall to seal a joint that had opened between the walls, according to the newspaper.
Those problems “should have alerted the owner and design team that issues existed with the integrity of the wall,” the report said.
In fact, the newspaper said, plant officials did outline problems to both towns’ officials as early as February 2009. Not until October 2010 did the owners hire an engineering firm, LMK Engineers of Pottstown, PA, to conduct a post-construction audit. The audit, released early this year, listed 157 construction deficiencies, the newspaper said.
A spokesman for the mayor “did not directly address questions about responsiveness of the owners to structural issues prior to the collapse,” according to the newspaper.
Delta Engineers, the firm that designed the collapsed wall, has declined so far to comment on EFI’s report.
Current Structure Studied
Meanwhile, other walls at the plant are showing signs of stress similar to those found in the collapsed wall, and a third company, C&S Engineers, is conducting a structural and safety study.
The Press & Sun-Bulletin reports that diagonal cracks are visible on other exterior concrete walls of the secondary treatment system, “darkened by apparent liquid seepage.”
Fourteen of the 20 treatment cells have been emptied and taken out of service since the collapse, reducing capacity from 60 million gallons per day to 45 mgd, a plant spokesman told the newspaper.
Meanwhile, 40 union employees have refused to work in the secondary treatment area until it is declared safe, and seven management employees are running the system.
Lawsuits and More Reports
Longer term, the plant’s owners have again commissioned LMK Engineers to conduct a structural investigation similar to EFI’s.
That report will likely be used in the plant owners’ recently filed lawsuit against 12 defendants, seeking $20 million in compensation for the construction problems.
Officials declined to answer two questions posed by the newspaper:
• Do the owners know if the outer walls of the treatment cells unaffected by the collapse have the same design as the collapsed cells in construction documents?
• Are the owners investigating whether the outer walls of the other cells could have design problems?
“If the question is whether our engineers believe that the remaining walls are in danger of imminent collapse, the answer is no,” a spokesman said.