Rain triggers 7.8M gallon sewer tunnel overflow into the Genesee River

Prolonged rainfall Sunday and Monday triggered the year's first sewer-tunnel discharge, a 7.8 million gallon discharge into the Genesee River.

The deep tunnel system, operated by Monroe County, was designed to collect stormwater and sewage that otherwise would be dumped into local waterways. The 30-mile-long tunnel system can hold 175 million gallons.

But when heavy rain fills the tunnels, the excess is discharged into the river or Irondequoit Bay. About 1 ⅔ inches of rain fell in Rochester Sunday and Monday.

In 2017 there were eight overflow events, the highest annual total in recent years.

The discharge Monday, from an overflow tunnel on the east side of the Genesee below Seneca Park, lasted 4.7 hours, according to a report filed by the county with New York state officials.

Most of the liquid in these discharges consists of rainwater and melted snow, though untreated sewage is mixed in as well.

County officials have said the overflows should have no lasting impact on water quality in the river or nearby Lake Ontario. The volume of wastewater being discharged is typically dwarfed by the flow in the river.

Like many older cities, Rochester has a combined sewer system — one that conveys sanitary waste from homes and businesses plus stormwater collected by gutters and curbside drains. Newer cities and suburbs keep stormwater flow separate from sanitary sewage.

Historically, many of Rochester's sewer mains would fill to brimming after sustained rainfall, and they overflowed constantly into the river and bay.

The deep tunnel system, built over a 16-year period beginning in 1977, captures that excess flow from the city sewers and stores it until the wastewater can be processed at the county treatment plant near Durand-Eastman Park.

Rochester is one of the few large cities on the Great Lakes with a large system to store and treat combined sewer flow.

SORR@Gannett.com