A burst of flames under a bulldozer blade stopped work Wednesday morning at Hanford's large landfill for low-level radioactive and hazardous chemical waste.

The Hanford Fire Department was called, but the fire self-extinguished immediately and firefighters determined no more action was needed.

Such flashes do happen occasionally at the Environmental Restoration Disposal Facility, said Washington Closure Hanford spokesman Todd Nelson.

But this one was accompanied by an unusually loud bang that the bulldozer operator heard over the sound of the equipment in an enclosed cab and workers about 1,500 feet away also heard, said Dave Einan, environmental engineer for the Environmental Protection Agency.

Washington Closure sent out an abnormal event report to state and federal officials on the incident, although it said the apparent chemical reaction did not meet emergency or abnormal event criteria.

The flash occurred when the bulldozer was spreading out a damp pile of soil contaminated with mercury that had been treated by a proprietary process of ADA Technologies of Colorado. The soil, which was excavated near one of the Hanford reactor sites, was mixed with a bonding agent and dropped into one portion of the landfill.

A fixative had been sprayed over it to make sure particles of the soil did not become airborne before the treated dirt was scheduled to be spread out Wednesday.

There was no evidence of a release to the air or exposure to hazardous materials, Washington Closure said. The soil is believed to have little or no radioactive contamination.

Work resumed later in the day at other disposal cells at the landfill, but work will not resume in the area of the flash until an investigation is completed, according to Washington Closure.

EPA also wants to know more about what caused the flash before treatment resumes of the mercury-contaminated soil, Einan said.