MAGNA - Kennecott Utah Copper Corp. insists its massive mine-waste pile is safe. And, based on the company's data, state regulators agree.
    The company says it has invested two decades of engineering and state-of-the-art construction to stabilize an archaic mud pool and build a new impoundment. The new $536 million facility underwent a years-long design review and technical analysis by some of the nation's leading experts.
    The old impoundment near Magna, once unstable and now unused, has been upgraded to the point that Kennecott is confident it does not pose the danger it once did - even in the worst earthquake predicted along the northeastern edge of the Oquirrh Mountains.
    The company has spent more than $13 million on the project, and all but a small portion of its southeast corner now meets the state's minimum safety standard, according to Kennecott.
    "Our goal is for it to be stable, and we continue to work on that," said Paula Doughty, Kennecott's manager of tailings and water services. "We have been working on that for the last 20 years, and we have seen the improvements."
    David K. Marble, who oversees Utah's Dam Safety Office, called it "basically safe."
    Yet, state records say little about the southeast corner, the section that looms over a MagÂna subdivision. By comparison, Kennecott's highly publicized work on the new north impoundment is detailed in more than 21 volumes of studies done over 15 years.
    With responsibility for more than 900 high-, medium- and low-risk dams statewide, Marble noted that the company is obligated to turn over copies of any reports he requests. And he says Kennecott has been "100 percent upfront" with necessary information.
    Doughty says engineering studies on the old impoundment - and there appear to be over a dozen - are available to the state upon request. But the state has not asked for any - nor is there any record of a state or third-party analysis.
    But company studies presented to The Tribune appear to show dramatic improvement at the southeast corner. Engineers used to think the old impoundment, also called a tailings dam, was too vulnerable during a large quake. Ground shaking might have turned the impoundment's saturated insides into a muddy avalanche, which could flow a mile north, three-quarters of a mile east or a half mile south toward MagÂna. Hundreds of nearby families could have been buried in mud.
    That discovery prompted Kennecott officials to stabilize the old Magna impoundment and shift operations to a new, state-of-the-art pond for tailings along the reinforced northern edge of the old one.
    The company has strengthend the old impoundment with:
    * Stepback dikes on the problematic southeast corner and small berms near two residential areas.
    * Wicks and a drain system to extract water from the old impoundment's interior.
    * Ground-shaking monitors that trigger warning signs to keep drivers off State Roads 201 and 202 in the event of a quake.
    Now the top of the old impoundment, at 220 feet, looks more like a patch of dry Kansas plain than the watery waste pool it was for nearly a century.
    "We're not saying we're to the point that we are satisfied," said Doughty. "We continue to improve."
    Dam-safety supervisor Marble says the state's authority to regulate the old impoundment has been limited because it was historically designated only as a "moderate hazard" dam. But he is confident, based upon Kennecott's data, that it poses little risk now.
    "The state did what they could," he said. "And time has shown that what transpired on [Kennecott's] part and the part of the state has worked."
    Zip Zavodni, a Kennecott geotechnical engineer who has been part of the tailings impoundment improvements from the start, called the company's work the biggest seismic upgrade in Utah history and a world-class project of which he is extremely proud.
    He said you would have to be in exactly the wrong spot at exactly the wrong time to be hurt by it now.
    "If you add all that up," Zavodni said, "you have to be one hell of an unlucky person to get caught in this thing."
    fahys@sltrib.com
   
   How the new impoundments are rated
   
    The state Engineer's Office has two basic standards for the required strength of both the old and new impoundments. They are set out in a 1992 letter between Kennecott and the state Engineer's Office.
    One standard is for an Operating Basis Earthquake (OBE), or the kind of groundshaking that might be expected during the impoundment's working lifetime. After an earthquake, the required factor of safety must be at least 1.3, which means it must maintain its working strength after slightly more than the predicted shaking.
    Another key standard is the Maximum Credible Earthquake (MCE), or a worst-case temblor. After an earthquake of that magnitude, the impoundment must meet a safety factor of 1, but it can show signs of weakness though not enough damage to allow "a major release of tailings resulting in a threat to public health, property and/or present a public safety risk."
    Kennecott says it has designed the impoundments for an OBE of 6.5 and an MCE of 7.25. The new impoundments meet both standards, the company says.
    (In measuring the strength of earthquakes, the higher the number, the more severe the quake. For instance, the Loma Prieta quake that rocked California in 1989 measured a magnitude of 6.9. The strongest earthquake predicted for the Salt Lake Valley is a 7.5.)
    But a small area of the southeast corner meets a safety factor of only 0.7 under MCE conditions - which means it falls short of the state's minimum standard for the worst-case quake. Kennecott needs to lower saturation in the old impoundment an additional 20 feet to meet the safety factor of 1.
    Even if there was a strong earthquake, a small area might glop over State Road 201. But the tailings would not stream out beyond, Kennecott says.
    -The Salt Lake Tribune