A toxic-waste site in Summit County that contains high levels of silver, zinc and lead mill tailings has been added to Environmental Protection Agency's Superfund list.

The 160-acre site, known as Richardson Flat, is at the junction of U-248 and U.S. 40, northeast of Park City. It was home to Keetley Mine, a silver, lead and zinc mine that ceased operations in April 1982.The next step in the cleanup, said David Schaller, chief of the EPA's regional office in Denver, is a remedial investigation. Soil, air and water samples are monitored more extensively than original tests.

The tests were conducted nearly two years ago, Schuller said. Richardson Flat, the second Summit County site to make the EPA's list, is one of 229 sites the federal agency studied for potential cleanup.

Utah now has the option to oversee the data collection effort, he said, but thus far the state had not indicated whether it will accept the EPA's offer.

The flat was used for depositing excess tailings while the mine was active, and EPA authorities set up monitoring stations between 1985 and 1988.

The tests showed arsenic levels 50 times higher than background samples, arsenic 60 times higher and lead 100 times higher, officials said.