The cities of Binghamton and Johnson City, N.Y., and their Joint Sewer Board have filed a $20-million suit against 12 companies, charging them with professional negligence and malpractice after a 100-ft wall collapsed in May.

The suit, filed July 22 in Broome County Supreme Court, also cites breach of contract and seeks “repair and replacement of various design and construction errors at the Binghamton-Johnson City Joint Sewage Treatment Plant, including, but not limited to, replacement of collapsed exterior walls, defects in design and construction of the Phase III improvements, methanol and BAF systems, removal of debris, replacement of filtering materials” and other costs.

The May 16 collapse involved four of 20 filtration cells at the plant, which underwent a $67-million Phase III upgrade in 2004-2006.

The plant has been providing secondary treatment since the event, which dumped 580,000 gal of partially treated wastewater into the Susquehanna River. The spill did not cause significant environmental damage, according to state officials.

One of the defendants is C&S Engineers Inc., of Syracuse, N.Y., which served as construction manager for the expansion project.

Bob Duclos, C&S vice president, said the company had not been served so “it would be inappropriate and untimely to make any comment.”

But, he says, C&S has been working with the owners since the collapse to make sure it was safe for operation and use by employees.

Union employees refused in June to enter the damaged area, citing safety concerns and a leaking control system roof, forcing seven non-union workers to handle operations in that area.

After two years of problems reported in the plant, the then-chairman of the sewer board last summer e-mailed board members and city officials photos showing wall separations, chipped concrete and leaks.

That resulted in a construction audit by LMK Engineers LLC of Pottstown, Pa., that found more than 150 construction deficiencies, including “inadequate construction management,” “vague or missing” expansion joint details between treatment cells and “numerous leaks” at intersecting cell walls.