A valve malfunction led to a spill of about 17,500 gallons of untreated sewage in the Pearl City area yesterday, the city said.

The Pacific Palisades Pump Station's 10-inch steel force main became obstructed when an isolation valve in a manhole on Komo Mai Drive failed. That blocked the flow of wastewater, causing the station's backup well to overflow.

The city said 16,389 gallons of untreated wastewater reached Waimano Stream, which empties into Pearl Harbor. In addition, another 1,154 gallons came out of the manhole during repairs and went into a storm drain that led to Waimano Stream.

City crews repaired the valve and were able to collect 105,000 gallons of sewage and transfer it back into the treatment system.

The city notified the state Department of Health. City crews posted warning signs and disinfected the area.