Twenty power plants, from the Humboldt Bay plant to the South Bay plant, would have to spend almost $31 million altogether to comply with Environmental Protection Agency rules posted this month to control the killing of fish in plant intake cooling water. However, generators say it might cost more than the EPA predicts and they do not know what technology the agency will find acceptable. ?I think that in some cases the cost may be higher than what EPA thinks,? said Jesus Arredondo, NRG Energy director of regulatory affairs. He said that NRG operates ?to ensure that we are using the best practices,? but the company doesn?t know the details of the new regulations. In general, the agency calls for using the best available technology to avoid fish destruction. Power plant operators have three years to comply. According to Arredondo, owners have to draw up plans for conformance, and then the agency can accept or deny those plans. California power plants? combined total intake for cooling is almost 18 billion gallons a day, according to the federal government. Two hundred forty-eight species are ?impinged and entrained,? i.e., dispatched to fish heaven, by power plants in the state. Nationwide, power plants suck up an average of more than 214 billion gallons a day for cooling. The San Onofre Nuclear Generating Station, for instance, is estimated to kill 57 tons of fish a year, and densities of local fish decreased by up to 70 percent within three kilometers of the plant. However, bottom-dwelling fish numbers were higher because of the plant?s warm output. Not just coastal plants are on the agency?s radar; the EPA noted that intakes at the Pittsburg and Contra Costa power plants may be affecting Delta smelt and green sturgeon. Diablo Canyon owner PG&E expects environmental groups to challenge the rule, ?which would mean it could be changed,? according to PG&E spokesperson Jeff Lewis. ?So it is premature for us to take any action until these challenges are settled.? He added that water-quality agencies are waiting to see what happens so they can determine how they will apply the rule. ?When the rule is finalized, we will do what?s necessary to be in compliance with it.?