A power outage at the Harford County wastewater treatment plant in Perryman this week caused nearly 100,000 gallons of raw sewage to spill into nearby wetlands.
The untreated water drained into the Sod Run wetlands Tuesday and might have reached Sod Run, which feeds into the Bush River, according to the Maryland Department of the Environment, which investigated the spill.
"It is a fairly large marshlands area, and wetlands are good natural filters, but with the tides, it is possible that the spill mixed into Sod Run," said Chuck Gates, MDE spokesman.
The spillage will decompose naturally in the swampy area, county officials said. Though plant workers will monitor the site, they will not be taking samples. The marsh area, which has been posted with details of the spill, is not open to anglers, boaters or the public.
"The wastewater is in a swamp, basically mixing with mud, so it is difficult to pull samples," said Wayne Ludwig, county operations chief for water and sewer. "We will monitor visually and clean up any materials in the spilled wastewater. The swamp will naturally break down the organic matter, nutrients and germs."
Raw sewage is mostly water with .03 percent pollutants. According to the amount of spill, Ludwig estimated it would have about 30 pounds of nitrogen and six pounds of phosphorus.
Germs will be neutralized within five days, he said. Nutrients and organic material will decompose in about two weeks.
The plant, which processes 13 million gallons of sewage daily, was conducting a planned power outage that allowed workers to work on the power system.
Crews inadvertently disabled the computer that runs the pumps, officials said. Without the computer, the pumps sat idle and allowed incoming wastewater to overflow. The spill was discovered within about 20 minutes, officials said.
A similar maintenance check on the power system was completed three years ago without incident, Ludwig said. Plant engineers will review the entire maintenance process in hopes of averting any future problems, he said.
"We are fairly confident they are taking the right steps to prevent a recurrence," Gates said.
In addition to MDE, plant officials have notified the county health department.