The treated sewage discharged into the ocean from city's Sand Island Wastewater Treatment Plant does not meet water quality standards set to protect marine life or human consumption of fish, the EPA said.

Today's decision is tentative, and follows a similar EPA finding in March regarding the Honouliuli treatment plant, the city's second largest. Both facilities have long held federal waivers that allow them to operate without performing a process called full secondary treatment, which is required at nearly all other U.S. sewage plants.

The two facilities handle the bulk of O'ahu's wastewater, but the city contends that upgrading them would be unnecessary and could cost $1.2 billion. The money would be better spent on other projects, including repairs to the island's crumbling network of sewage pipes, officials argue.

But the EPA recently found that bacteria levels around the Honouliuli plant's discharge outfall were higher than national standards adopted in 2004 to protect swimmers, surfers and others from gastrointestinal diseases.

The agency also found that the plant's effluent often proves toxic to sea urchins, and produces excess ammonia that can harm other aquatic organisms.

The city has appealed the tentative denial of the waiver for Honouliuli, and had indicated it would do the same if the Sand Island waiver were denied, as was expected. A city spokesman was not immediately available today.

The EPA has scheduled a hearing for the public to comment on the Sand Island finding, to be held on Feb. 5 at 6:30 p.m. at Washington Intermediate School.

In a voluminous response to the Honouliuli finding, the city contended that the federal agency's "tentative conclusions are not supported by ... monitoring data, and are often arbitrary, conclusory, speculative, or not rationally related to the waiver criteria."

The quality of effluent from the plant has improved since the waiver was first granted in 1988, according to the document. The EPA is reviewing responses from the city, scientists and the public, but has not set a date for a final decision.

The agency said today that improvements are needed at both plants.

"These upgrades will ensure that Hawai'i's residents, visitors and marine life benefit from the full protections provided by the Clean Water Act," said Wayne Nastri, the EPA's administrator for the Pacific Southwest region.