For the third straight day, municipal wastewater passed through Hagerstown's sewage treatment plant and into Antietam Creek, a Potomac tributary, without being subjected to microbial action that normally kills the dangerous germs in raw sewage. The plant processes as much as 5.7 million gallons of wastewater daily. The biological process was stopped Saturday by an unidentified chemical substance that was poured, dumped or accidentally released into the sewer system, officials said.
The substance, which contained the common solvent toluene, killed the microbes. It might have come from an industrial user or, in a less likely scenario, been poured down a manhole, said Donald Barton, the plant superintendent.
He said more testing is needed to identify the chemical substance, but "it isn't something we would normally see in domestic waste."
The plant is growing new microbes. In the meantime, it may start treating the wastewater today with chlorine, a substitute disinfectant, until the microbial action resumes, Barton said. The wastewater will be dechlorinated before it is released, he said.
The plant has continued treating the wastewater with a primary step that removes solids. The effluent being discharged into the stream yesterday was clear but foamy and did not have a noticeable odor.
Officials said it could be tomorrow before the contamination plume reaches Brunswick, the first sizable downstream community currently relying on the Potomac for drinking water. The river also supplies water to the District and many of its suburbs.
State environmental regulators said the wastewater will be highly diluted and pose no threat by the time it reaches the intake pipe for Brunswick's 6,200 water users.
Maryland Department of the Environment spokesman Richard McIntire said the contamination did not appear to be bothering or harming waterfowl.
There were no signs of any fish kills, either, state Department of Natural Resources spokesman John Surrick said.