Central Valley regulators have tentatively signed off on the air pollution expected to be generated by the Hydrogen Energy California power and chemical plant proposed near Tupman.

While a full project approval is at least several months away, the preliminary determination of compliance issued last week by the San Joaquin Valley Air Pollution Control District signals that HECA appears to meet its various requirements.

It means that even though the project's emissions would exceed otherwise acceptable levels, HECA has mitigated these negative impacts, and its pollution-control equipment is the best available.

The district's finding opened a public comment period set to end at 5:30 p.m. April 17.

As proposed, HECA would produce nitrogen-rich products including fertilizers. Alternately, during times of peak demand for electricity, the 453-acre project would generate about 300 megawatts of power.

It would also create up to 200 permanent jobs and provide a test of carbon-burying technology. The project has been subsidized by a $408 million grant from the U.S. Department of Energy.

Project neighbors and environmental groups have reacted angrily to the district's preliminary finding.

"This is completely irresponsible," local environmentalist and farmer Tom Franz stated in a news release. "We already breathe some of the dirtiest air in the country. The air district is ready to hand HECA a permit to give the people of Kern County more asthma attacks and health problems."

District staff have determined that the project's emissions would exceed allowable thresholds in five categories: nitrogen oxides (1,587 percent of the district's threshold), sulfur oxides (109 percent), fine particulates (613 percent), carbon monoxide (272 percent) and volatile organic compounds (377 percent).

(The project's byproduct carbon monoxide -- 3 million tons a year of it -- would not be vented to the atmosphere but piped to a neighboring Occidental Petroleum Corp. site to promote oil production. After that the gas would be stored underground indefinitely.)

Air district staff determined that HECA's proposed nitrogen oxide emissions would exceed those of other "modern" power plants in California by 19 percent. To mitigate that difference, HECA's Massachusetts-based owner, SCS Energy LLC, agreed to pay fees that the district intends to award in terms of grants and incentives geared toward reducing emissions around the Central Valley.

SCS has also purchased what are known as clean air credits to offset the project's expected air pollution.

For example, SCS acquired nitrogen oxide and sulfur oxide credits that became available with the shutdown of the former Big West refinery on Rosedale Highway in 2009. The refinery's subsequent owner has since reopened and re-closed the plant several times without affecting HECA's clean air credits, which records show the company bought in November 2009.

A HECA spokeswoman said Tuesday that the company does not need to buy any more air credits for the project.

Ultimate approval of the HECA project will be up to the California Energy Commission, which is scheduled to decide on a final permit later this year.

SCS Energy hopes to start construction this year and begin operations by the end of 2017.