C&S personnel have been at the plant since the  collapse, checking safety and performance while assessing the site, he  said, but it is too early to speculate about a cause.

The plant, with a 26-mgd capacity and maximum flow of 60 mgd, serves Binghamton, Johnson City and seven other area cities.

The failed wall houses part of the biological  aerated filtration system, built as a result of an agreed order to meet  state requirements for water quality released into Fuller Hollow Creek,  the Susquehanna River and eventually Chesapeake Bay.

It is the Susquehannas second-largest public wastewater treatment plant, after Harrisburg, Pa.

The owner selected a biofilm aerated filter (BAF)  system, a three-stage process for carbon removal, nitrification and  de-nitrification, because of the plants limited space for expansion.