Sewage from a broken 16-inch sewer pipe began pouring into the Reddy Branch Creek in woods near the 19600 block of Olney Mill Road in Olney late Tuesday morning, Washington Suburban Sanitary Commission officials said.

The sewage spill -- at a rate of 100 gallons per minute -- began at 11:30 a.m. and was still occurring as of 5 p.m. Tuesday, WSSC said. Unlike most sewer lines that use gravity to move the contents, this broken line is pressurized, officials said.

Some sewage also is overflowing at the Reddy Branch wastewater pumping station, officials said.

The cause of the break is still being determined. State environmental officials have been notified, and a contractor is on the scene, WSSC said.