Ron Henline remembers that about 10 years ago some signs went up along a few roads in Magna that said to take alternate routes when some strategically placed lights were flashing.

A blinking light then, and now, would mean a section of an earthen embankment used by Kennecott Utah Copper Inc. to keep mining waste contained in its old south "impoundment" had, perhaps because of an earthquake, ruptured and that a release was on the move.

"I didn't think much about it," said Henline, currently a member of the Magna Planning Commission and resident of the same Magna home for 44 years. "We've all been aware for a lot of years that the dike, in its original form, was subject to liquefaction in a strong earthquake."

But on Monday morning Henline had not seen a collection of articles published in the Salt Lake Tribune Sunday about old documents that point to past concerns over "seismic instability" at a corner of the 100-year-old, 5,700-acre tailings impoundment.

Paula Doughty, who manages tailings and water services for Kennecott, said a major earthquake today of about 7.25 magnitude could potentially disrupt about a 20-foot section of the impoundment on its southeast corner, known as the Magna Corner. It's possible, she said, that there would be a muddy "release" of mining waste that could move over 2100 South. How much or how fast, she wasn't able to say.

"I do not believe there is a level of concern for residents in Magna today," Doughty said over the phone Monday. She cited efforts over the years to shore up the Magna Corner.

One neighborhood in particular, the Meadow Green Estates subdivision, was once a major concern of Kennecott officials who were worried that a breach in the tailings pond might flow into homes.

"We don't have any concerns with that neighborhood today," Doughty said.

The reason being that the south impoundment has been retired.

"It no longer holds water," said David Marble, an assistant state engineer over dam safety throughout Utah. "It's no longer a dam — it's inactive. I think that's kind of a central question to this whole thing."

The state still eyeballs the Magna Corner annually, but Marble's focus is on the north impoundment, which does hold water. He said there are state documents that highlight past concerns about the Magna Corner. But Marble wasn't aware of any state records that suggested a possible cover-up by Kennecott.

But a 1997 document the Tribune found shows what appears to be evidence of Kennecott's efforts to hide the seismic risk from Magna residents. That document states that Kennecott's land development arm went so far as to purchase 39 homes in Meadow Green Estates and then rent them and eventually sell them, all allegedly without disclosing the risk to tenants or buyers as Kennecott worked to fix the problems at the tailings pond.