Historic Mountain Dell Dam near Salt Lake City listed as 1 of 5 of Utah’s high-hazard dams

The windowlike arches on the outside of the towering Mountain Dell Dam provide an artistic facade that fits with the natural beauty of the Utah mountain canyon where the century-old structure sits.

The design's historical significance earned it a spot on the National Register of Historic Places and a designation as an American Water Works Association Landmark.

But the concrete structure also sits on a less desirable list: It is one of five dams in Utah and at least 1,688 in the United States that are in poor or unsatisfactory condition and located in places where a breach would likely kill at least one person, according to an investigation by The Associated Press.

The Mountain Dell Dam is 5 miles east of Salt Lake City next to a heavily traveled stretch of Interstate 80 that connects residents and tourists to the mountain resort town of Park City, where many events in the 2002 Winter Olympics were held.

The dam is listed in poor condition because of deteriorating concrete that allows seepage from the reservoir, said David Marble, Utah assistant state engineer. The dam is only allowed to be about half full in the winter because of what is known as a "freeze-thaw problem," which refers to erosion that occurs when concrete cracks get worse over time after freezing and thawing, he said.

Salt Lake City, which owns the dam, is currently installing a liner system on the upstream face of the dam in an attempt to slow the leaks. The $3.1 million project is one of several done in recent years to ensure the dam doesn't reach a critical level, said Bernard Mo, the city's storm water capital improvement program manager who is responsible for dam safety.

"We've been monitoring this for years," Mo said. "It's not like we're leaving alone an unsafe dam."

State officials had been "leaning on" on the city to address the dam, and the repairs are substantial, Marble said. "This is not just a little glue," he said.

A dam failure would close the highway in the canyon and lead to potential flooding downhill in the eastern parts of Salt Lake City, including near a popular park, according to an emergency action plan produced in 1994 and updated in 2010.

But Marble and Mo insist the dam isn't at risk of that, which is why it's not in the "unsatisfactory" category for dams. Utah doesn't have any dams in that category.

Overall, Utah dams are in pretty good shape compared to other states.

Just 2% of Utah's 241 high-hazard dams are in poor condition, one of the lowest rates among 44 states and the U.S. territory of Puerto Rico that provided the AP with full data. High hazard is a category that doesn't refer to the dam's condition, but rather the fact that a failure could lead to loss of life.

Utah's dam safety budget has increased 18 percent since 2010 to $866,000 this year, according to data obtained by the AP. The state has repaired 55 dams over the past two decades at a cost of $198 million in state and federal money. Marble said 84 dams remain on the state's fix-it list.

The program has shored up some of the state's most at-risk dams, including one at Fairview Lake in central Utah that had a leak that was letting out enough water per second to fill a basketball, Marble said.

"We had quite a few that you would call a 'leaker' and a 'saggers' that we were very concerned about," Marble said. "I sleep a lot better at night because of the work we've done over the last period of time."

The other four Utah high-hazard dams listed in poor condition are smaller irrigation dams that are privately owned.

The top of the concrete wall is deteriorating on the aging Red Pine dam deep in the mountains east of Salt Lake City, a few miles downhill from the Snowbird ski resort, Marble said. Some temporary repairs are being done.

A state restriction has been in place for about a decade limiting the owners of Jones dam east of Heber City from filling it more than about halfway due to seepage issues, Marble said. The small dam is near a smattering of homes.

State officials didn't even know about the Alton Reservoir irrigation dam in southern Utah until a few years ago and are working with the owners to make sure it's in satisfactory condition, Marble said.

The Palisades Lake dam in central Utah near a state park that offers hiking, camping and fishing has some seepage, he said. The dam is on a state list to be repaired sometime in the future, Marble said.