Coal measures: PSNH emissions system challenged.

Three businesses and a competitor of Public Service of New Hampshire are calling on state regulators to take another look at the utility's plan to upgrade its coal-burning plant in Bow.

They say the new review is warranted because the cost of the emission reduction project has risen dramatically, from $250 million to $457 million.

The Legislature passed a law in 2006 requiring PSNH to build a scrubber to reduce mercury emissions. Ratepayers will pay for the project.

The Public Utilities Commission ruled in September that it had no authority to review the project. But on Oct. 17 the commission received two motions for another review, one from TransCanada Hydro Northeast, a hydroelectric generator, as well as from three businesses: the Common Man restaurants; yogurt maker Stonyfield Farm; and H&L Instruments of North Hampton, which makes electro-optical equipment. They argue that the state should take a longer look at how the Bow plant fits into the state's long-term energy plan.

Public Service said it's disappointed the challenge comes as work is about to begin on the project.