Natural gas bills across Long Island would see a 2.7 percent increase in January 2011 tied to unexpectedly higher costs to clean up toxic coal-tar sites around Long Island, National Grid said, in filing a rate increase request.

In January, the London-based company filed a request with the state Public Service Commission seeking to increase rates based on "significantly" higher spending to investigate and clean up the toxic sites, which supplied manufactured gas for heating and lighting during the past century.

All of the sites, affiliated with the former Long Island Lighting Co., are closed, and some have already been cleaned up.

But National Grid has spent much more money working on the largest sites on Long Island than it expected when it first requested ratepayer funding for the cleanup three years ago.

In the PSC filing, National Grid costs to clean up toxic sites on Long Island are expected to jump $71 million this year alone. That's atop some $199.3 million the company has already spent investigating and cleaning up sites from Sag Harbor to Hempstead since it bought KeySpan in 2007.

Most of the increase, National Grid said, was tied to cleanups at the largest toxic sites in Bay Shore, Hempstead and Rockaway Park. Ratepayers on Long Island already are funding $10 million a year to help defray the costs.

National Grid said it expects the costs to gradually decline on Long Island, but nevertheless will exceed $20 million a year through the end of 2012.

National Grid spokeswoman Karen Young said the 2.7 percent increase will amount to around $60 a year for the average ratepayer who uses 140 decotherms of natural gas. Commercial and other large users will pay more.

The filing also asks for an increase related to toxic plant cleanups in New York City for another National Grid division. That increase amounts to 1.7 percent, or around $38 a year for the average user, Young said.

"We take our obligation to do the remediation work seriously . . . and we're making significant progress," Young said.

If approved, the rate increases would begin in January and would remain in effect for "rolling five-year periods." PSC spokeswoman Anne Dalton said the case is pending and will be ruled on following a public comment period that ends July 31.

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