State health officials are investigating potential contaminated storm water runoff into the ocean from the city’s Waimanalo Gulch landfill in Leeward Oahu.

State health spokeswoman Janice Okubo said yesterday the discharge began Sunday after heavy rainfall and continued through Thursday between Ko Olina and the Kahe Power Plant.

Okubo said the city is required to report discharges into the ocean. "We are still investigating it," she said.

A state Health Department solid waste inspector discovered the water runoff on Thursday, she said.

The inspector notified state Clean Water Branch officials, who are conducting an investigation.

City spokeswoman Louise Kim McCoy said landfill operator Waste Management of Hawaii followed protocol and notified the state Solid Waste Branch on Monday of the discharge.

She said state Clean Water Branch inspectors visited the landfill Tuesday.

"The Health Department did not raise any issues or concerns at that time," she said.

Waste Management pumped storm water from the top of a landfill cell that had last received solid waste last Saturday and had been closed with a 10- to 12-inch layer of soil, the city said in an e-mailed response to Star-Advertiser questions.

"At no time was the storm water mixed with any solid waste," the statement said.

Pumping excessive storm water from the top of a cell is a permitting activity and is common practice, the statement said.

Okubo said the landfill will test water samples.

Okubo said warning signs were not posted because state health officials were not sure about the concentration of potential pollutants and felt the discharge had dissipated in the ocean.

Okubo said officials did not know how much potentially contaminated water entered the ocean.