Last night's power outage shut down ultraviolet disinfection units at the City's Wahiawa and Sand Island Wastewater Treatment Plants before backup diesel generators engaged.

The UV units were inoperable at Wahiawa WWTP for 16 minutes (6:46 – 7:02 p.m.), while at Sand Island WWTP the units were down 20 minutes (6:30 – 6:50 p.m.).

The Wahiawa plant discharged 30,880 gallons of tertiary treated effluent without disinfection into the Wahiawa Reservoir through its outfall, according to a City news release. An estimated one million gallons of primary treated effluent without disinfection was released through Sand Island WWTP's deep ocean outfall, according to the City.

The City notified the state Department of Health.

Warning signs are being posted in the effected areas.