The state Department of Health has imposed a $542,000 penalty against the city for clean-air permit violations at the Sand Island Wastewater Treatment Plant.

The plant's hydrogen sulfide emissions exceeded allowable limits from February 2003 to December 2004, state officials said.

Bill Brennan, spokesman for Mayor Mufi Hannemann, said city officials have taken action to correct the problem this year and the city is no longer violating the standards.

Brennan said the city built a new headworks building at the sewage treatment plant that includes new air-pollution control equipment. He said that project was completed and began operating in August. Initial air-monitoring results show a marked improvement in air quality, he said.

State officials said the city was violating the air permit limit of 0.023 part per million at the property line of the Sand Island plant. City officials had reported the violations to the state as part of a city self-monitoring policy.

Hydrogen sulfide is formed by the decomposition of organic matter, smells like rotten eggs and is often present in septic tanks, cesspools, wastewater pumping stations and treatment plants.

State officials said that at higher concentration levels — 10 to 20 parts per million — the gas can cause temporary health problems such as headaches, dizziness, nausea and irritation to the eyes and respiratory tract.

Brennan said the city has filed a formal request for a hearing and requested a meeting to talk about progress made.

Health Department spokeswoman Janice Okubo said the state's stricter air-permit limit is meant to minimize the nuisance associated with the gas and provide a bigger margin of safety for the public.

State officials also ordered the city Department of Environmental Services to take action to comply with the permit.

Okubo said sometimes penalties can be negotiated, based on corrective action taken.

Brennan said the city also is including other air-pollution control equipment in other improvements being made to the Sand Island facility.

Reach Robbie Dingeman at rdingeman@honoluluadvertiser.com.