Trustees on Monday awarded a contract to a joint venture of Casey Industrial Inc. and Wheelabrator Air Pollution Control Inc. to install baghouses on the J.T. Deely power plant at Calaveras Lake by spring 2007.

The cost of the contract totals $87 million, or $21 million more than what staff projected.

Baghouses are multi-story warehouse-size structures filled with fabric filters that experts say act like vacuum cleaners to trap fly ash produced at coal plants and to keep the particles out of the air.

The Deely plant, one of CPS' two coal-fired plants, was listed by the U.S. Public Interest Research Group as one of the 548 worst- polluting coal-fired plants in the nation last year. It is called "Dirty Deely" by critics.

Purchase of the baghouses is part of a $316 million investment in environmental controls planned at the utility's current coal operations in order to fulfill a pollution reduction pledge.

CPS is seeking a permit to operate a third coal-fired plant but has said emissions from all three will be less than what the two current plants now produce thanks to the new controls.