Among the myriad breakdowns in infrastructure that can haunt a city, surely one of the worst is a major malfunction in its sewer treatment plant. By any standard, Tuesday's breakdown was staggering.
An electrical outage that knocked eight sewage pumps off-line at the Moccasin Bend treatment plant caused an enormous backup of incoming waste. Resulting pressure on pipelines to the plant from downtown, in turn, caused massive overflows at three major points, and poured 137 million gallons of sewage into the Tennessee River.
Mayor Ron Littlefield called the spill "a tragedy." His statement is on the mark.
One spill site, a manhole under the Market Street bridge, flooded the grounds of Coolidge Park. That prompted the mayor to promise, among other things, that the sod at the popular park would removed and replaced as soon as possible. Warnings went up elsewhere along the Riverwalk cautioning people about the spill and resulting contamination.
While City and state environmental officials made no attempt to downplay the spill, they noted that the massive volume of water that was being released by TVA from upriver dams following last Sunday's heavy rains significantly diluted the sewage and mitigated its organic effect downstream.
TVA officials aid the agency spilled 80 billion gallons of water downstream from its dams around the time the sewage treatment plant was blocked and spilling raw sewage for 18 hours. They calculated that would have diluted the sewage spill to 0.17 percent of the river's flow in that period.
In any case, water companies in Chattanooga and downstream towns reasonably went on alert for e-coli bacteria near fresh water intakes. They said they would monitor water supplies until the health threat passed.
That should assure area residents who on rely on the river for drinking and domestic water, but it should also prompt close attention to ways to ensure that such a massive spill will not happen again.
Mayor Littlefield's first response to such a threat was to promise the installation of a back-up generator to keep the Moccasin Bend plant operational in event of another major power outage. Whatever the expense, that's a sound decision. Indeed, given the sanitation and health issues, it raises the question of why no backup power system has ever been installed.
The plant's pumps were off-line for 18 hours before the city could procure two generators from a Knoxville contractor and get them hooked up and working. In the interim, plant officials searched for the cause of the outage -- it turned out to be worn insulation on an electrical line -- and worked to repair the cascading damage to the electrical system caused by breakdown, the worst in the plant's 49-year history.
City workers must also vacuum and disinfect spill sites and repair related damage. Attention to the ramifications of the spill will not, and should not, stop there.
Plant officials say they intend to review their inspection regimes at the plant, though they admit that would not necessarily identify the possibilities for the sort of random outage that caused Tuesday's breakdown. City officials also have acknowledged for years that the city's old mixed-use sewer lines, carrying both sewage and storm water runoff, need to be separated. That's a costly task, but it would reduce the volume of flow at the sewer plant that requires extensive treatment, and presumably ensure better treatment and expand capacity.
Finding a way to make the plant less vulnerable to another catastrophic failure may be more difficult. But given Tuesday's disaster, that cause requires persistent effort.