The Atlantic Richfield Co. has agreed to pay $21 million to the state of Utah and the Environmental Protection Agency to clean up mill tailings at the Sharon Steel Superfund site in Midvale, the EPA announced Thrusday.

In addition to the $21 million, ARCO has agreed to dismiss its counterclaim against the federal government.The agreement, contained in a draft consent decree, is expected to be filed soon in district court, according to the EPA. The public now has 30 days to comment on the agreement.

ARCO is the last defendant to settle in a 1986 suit brought by the government to force companies to pay for the cleanup of 14 million tons of toxic tailings.

Sharon Steel agreed in August to pay $22 million in cash or $82 million in cash and bankruptcy claims. A trust representing the now-defunct UV Industries agreed to turn over assets worth about $18 million to defray the cleanup costs.

If settlements with all three defendants are approved by the court, the lawsuit will not proceed, EPA officials said.

ARCO first announced a tentative agreement - but not the monetary amount - in mid-October. The federal government maintains that mill tailings containing toxic levels of lead, arsenic and cadmium are hazardous to residents and are polluting groundwater. The tailings are piled 40 feet high at the 260-acre site near downtown Midvale.

ARCO lawyers have argued the poison levels are too low to pose a public health danger.

The EPA has recommended capping the tailings pile and treating the groundwater at a cost of about $35 million. City officials have said they oppose that cleanup method, preferring instead that the tailings be taken off site either for disposal or reclamation.