FAIRBANKS — The Alaska Supreme Court says recent owners of a North Pole oil refinery share costs of cleaning up a contamination that has reached about 7 square miles of groundwater.

The Friday ruling keeps onsite cleanup costs attached to Flint Hills while former refinery owner Williams Alaska Petroleum is responsible for the plume that spread offsite, the Fairbanks Daily News-Miner reported.

“The record is pretty clear that neither company did very well in terms of looking for this problem,” Justice Daniel Winfree said, “but that’s not the issue.”

A Williams Alaska Petroleum attorney argued Flint Hills was slow to respond.

“Despite the advice to go out and find the sources, it doesn’t appear that Flint Hills has done much to find the sources,” attorney Randy Jones said in court. “So for four years of being told to look for sources, they didn’t look for sources.”

A nearby resident had sued Flint Hills over the contamination. Flint Hills then filed a claim against former refinery owner Williams Alaska Petroleum. Payments will be decided by the Superior Court. A spill of the chemical sulfolane caused the contamination.

An attorney says Flint Hills has spent “tens of millions of dollars” so far on filtered water for residents and refinery cleanup.

Offsite cleanup has not started.

“We are still studying the opinion, but overall we are pleased with the decision of the Alaska Supreme Court,” said Flint Hills spokesman Jeff Cook in a prepared statement. “We look forward to our day in court when these and other claims can be resolved.”