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Dust to blame for March explosion and fire at Back River Wastewater Treatment Facility

The Back River Wastewater Treatment Plant in Baltimore. Egg-shaped structures are digesters in the wastewater treatment plant process.
Baltimore County Government
The Back River Wastewater Treatment Plant in Baltimore. Egg-shaped structures are digesters in the wastewater treatment plant process.

An investigation by the Baltimore City Fire Department found that the March explosion at the Back River Wastewater Treatment Facility, which sits in the unincorporated community of Dundalk, was caused by dust that ignited in a sewer sludge dryer.

The findings, which were first reported by The Baltimore Sun, also ruled that the explosion was “accidental” — which occurred after sparks from the ignited dust then ignited the thermal oil, as well. That part of the facility turns sewage sludge into dry fertilizer pellets and is operated by the private contractor, Synagro. The report also mentioned unspecified “poor housekeeping” in a separate part of the facility but said “No signs or sources of ignition were observed in this area that would have contributed to the ignition of this fire.”

Synagro could not comment on the city’s investigation due to their own internal investigation, wrote Layne Baroldi, the company’s vice president of legislative and regulatory affairs. “Synagro is intimately familiar with the inner workings of our facilities,” wrote Baroldi in an email to WYPR. “Synagro’s investigation will be a thorough root cause analysis which will provide an in-depth look at the event. This step takes more time to complete due to the level of detail.”

The Back River plant falls under the auspices of the Baltimore City Department of Public Works, which told WYPR in an email it regularly inspects the privately operated facility in addition to reviewing maintenance logs and operations. DPW wrote, “The City will utilize its safety inspection team, in conjunction with third-party inspectors, and will continue its due diligence inspections of the facility. In addition, Synagro is installing improved monitoring and control systems.”

Although seven workers were inside of the building at the time of the explosion and subsequent fire, there were no injuries reported.

These findings differ from the “working theory” put out by the Maryland Department of the Environment in late March which theorized the explosion could have been due to a pipe leaking hot oil.

The Back River Wastewater Treatment Facility is normally run by the Baltimore City Department of Public Works. But in March of 2023, the Maryland Department of the Environment ordered the city into a consent order with the Maryland Environmental Service due to problems with pollution and equipment failures.

Currently, the Synagro pelletizing facility is running on reduced operations. The latest of the consent ordered reports from the MDE states, “Synagro is currently operating its three existing centrifuges, two temporary centrifuges, and a belt press while still repairing the on-site dryers. Synagro is also coordinating the hauling of the cake material for land application.”

Baroldi wrote to WYPR that work is “well underway” to get the dryers back into operation but that timeline is dependent on some factors like supply chain and contractor availability.

A spokesperson for the MDE wrote that the consent order for the plant has been extended through at least July; in April, the last full month after the explosion, the plant exceeded the level of discharge limits for phosphorus. For months before, the plant had hit its phosphorus targets. MDE says they are also investigating reports of five sludge discharge overflows in May.

Emily is a general assignment news reporter for WYPR.
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