The state's risk rating system has a problem. It relies on engineering studies that dam owners were ordered to complete about work needed to bring dams up to current standards. But such studies have never been completed on 35 "high hazard" dams.

So, they have been left off priority lists, and their true risk is unknown.

"We don't really know whether they are safe, or exactly where they would fit on priority lists," said Marble, who became head of the state's dam safety program last year. "At this point, we can't document that they are safe, so we're going to assume they are unsafe."

He said the state has begun a push again for completion of those studies by owners. With that, he said, 20 of those dams are at the point that they have started exploratory drilling or are well under way with preparations for studies. Most of the other 14 have started some preliminary work or expressed willingness to do so, he said.

He said the state has the power to restrict operations at a dam if an owner will not do the work in a reasonable period, "but we try to work with them in a positive proactive way." That includes reminding them of the "carrot" of state funding for upgrades.

Repair priority

For the 143 state-inspected, high-hazard dams where detailed engineering studies have been completed, the state created a risk score to prioritize them for repairs.

Risk scores could range from zero to a possible 775, based on numerous factors about dam conditions and how many people they could endanger. A score of zero meant the dam met all current minimum safety standards — and 45 dams initially received that score (or were constructed after standards were raised).

All others had problems and had an average score of 111.

Among the worst initial scores were: 635 by the Piute Dam on the Sevier River near Marysvale; 588 by the Holmes Dam on Holmes Creek above Layton; 480 by the Porcupine Dam above Avon, Cache County; 380 by Logan First Dam above Logan; and 363 by Rocky Ford Dam above Minersville.

All of them have since been repaired or replaced, although a second phase of construction at Piute is still under way. After construction, the dams' scores essentially become zero as they then meet all minimum safety standards.

"Holmes Creek Dam was a big concern," Marble said, talking about the highest risk dams. It is just two miles above Layton and the rest of the heavily populated Davis County.