Heavy rains cause sewage overflow into Mattawoman Creek

Backup pumps engaged at treatment plant to cope with stormwater surge

On Friday, the remnants of Hurricane Michael dumped 4 inches of rain around the Mattawoman Wastewater Treatment Plant south of Indian Head in less than 24 hours, causing an overflow of around a million gallons of untreated raw wastewater into Mattawoman Creek.

Gregory Boykin, the deputy director for utilities said that public works staff discovered the overflow at 7:45 a.m. at the back of the plant, just outside the back gate. Boykin said that a single manhole located at a junction point, adjacent to the plant’s main interceptor, was affected.

Crews had successfully contained the overflow by 1:30 p.m.

Boykin stressed that the spill was “heavily diluted sewage, atypical from what we process daily.”

The plant normally handles

about 14 million gallons a day. The stormwater pushed the total amount of wastewater in the system to more than 25 million gallons a day.

Following heavy rains, “inflow and infiltration” — stormwater runoff that leaks into the sewage lines through cracks and gaps in manhole covers — can continue draining

into the sewer system for several days, Boykin said.

“Keep in mind, citizens do not change their flushing habits in a single day by 11 million gallons,” Boykin said.

Boykin said that all of the plant’s pumps were working and available throughout the storm. The plant also brought its two diesel-powered emergency backup pumps online to help cope with the excess influx of water.

Boykin noted that the overflow did not occur at any of the recently reinforced manholes close to the treatment plant, as had occurred in previous overflows.

The utilities division is in the process of rehabilitating the insides of manholes and bolting down their covers along the entire length of the main sewage line that leads into the treatment plant.

Manholes closest to the treatment plant were upgraded first, and crews are slowly radiating out to work on manholes further from the plant. These upgrades will allow the line to hold almost twice the pressure of wastewater than before.

The utilities division posted notices along Mattawoman Creek alerting people to the spill. The county government cautioned residents to avoid contact with the creek and encouraged them to contact them with questions or concerns at 301609-7400.

In June, heavy rains combined with the failure of two of the plant’s four pumps resulted in an overflow of approximately 5.8 million gallons of raw wastewater into the Mattawoman Creek watershed. It took over seven hours for DPW staff and contractors at the plant to bring that particular incident under control.