ST. GEORGE — After a 12-by-9-foot boulder crashed into a home and injured a woman, the city is looking at their development approval process.

About 3 a.m. on Jan. 19, Wanda Denhalter, 63, was sleeping alone in her home at 1681 E. 50 North Circle in St. George when she was awoken by a boulder crashing into her home. The woman was injured badly by the boulder, which crashed into the side of her king-sized bed.

The house, the Denhalters later found out, was built in a determined rockfall hazard zone. The couple, who was renting the house at the time of the incident, has since moved while the homeowner, Doug Alger, works to remodel it and mitigate the rockfall hazard.

Bill Lund, Senior Scientist for the Geological Hazards Program for the Utah Geological Survey, said that in the last month, several boulders have fallen into homes or outbuildings. The one that injured Denhalter, however, has brought the issue closer to home.

About two weeks ago, Lund looked at a proposed subdivision in St. George with a developer and city representative.

"We looked at everything and the developer said, ‘you know what, we've got 11 lots here that are in a hazard zone, if we put houses in there they would be at risk, people in them would be at risk,' " Lund said.

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The developer pulled the 11 lots from the original plan and readjusted the subdivision plans so that no occupancies would be at-risk. Both he and Marc Mortensen, Assistant to the City Manager, said that was a good example of being responsible and mitigating hazards.

"Our first recommendation, is if you can do it and it's not too costly, you should avoid the hazard," Lund said. "Just don't put your structure there and then you don't have to worry about it."

Mortensen said the city has no plans to change their "fairly restrictive hillside ordinance" but they do intend to change the development approval process to include a staff review of the hazard with the applicant.

Currently, the approval process gives the St. George City Hillslope Review Committee responsibility for approving all development plans in possible hazard areas according to the city ordinance.

According to Lund, the development in which Alger's house sits was developed after that committee was formed, but after Lund and the UGS created and distributed to cities throughout the state a series of hazard maps. Those maps will play a greater role in the future development process, Mortensen said.

"Our advice is that our hazard maps exist now, that a city should compare the location of the proposed subdivision with our maps to see whether or not it's in a hazard zone … and see if there's a hazard," Lund said. "And if there is, we think that should spark a site-specific study."

By the city ordinance, a portion of Alger's third-of-an-acre lot is unsafe for building construction due to the hill's steep slope. According to Mortensen, information about these hazards are included in the subdivision plat. Developers and homeowners assume legal responsibilities for these hazards.

"I never thought I would have had this situation," Alger said. "Looking up with the naked eye you think ‘there's no way a rock would fall that far.' "

The cause for the boulder breaking off has been pinned on a severe water leak coming from a vacant house sitting atop Foremaster Ridge above Alger's house. About 40,000 gallons of water were leaked into the porous sandstone above Alger's house.

"You could see the formation was wet," Alger said. "One of the neighbors could hear dripping from the hill. That leak happened over the course of one week and the week was really cold."

Alger said there are still significant cracks in the formation above his house and he is working to mitigate the hazard. He is working with Rosenberg Engineering to mitigate the problem using a trench and berm on the un-buildable portion of his property.

"I want to be part of the solution, not part of the problem," Alger said. "I think a lot of people who are involved with this … would like for this to quietly go away. But I think if people want to work together and come up with a good solution, that's possible, But unfortunately I think a lot of people just want it to go away."

Alger said that 25 houses are in hazard zones along the bottom of Foremaster Ridge.

"The question arises: the original developer who put in the lots, did they do their due diligence?" Alger said.

Mortensen advised developers and homeowners to get all the facts before making their purchases. He urged potential home-buyers to obtain the subdivision's plat and look over it for any hazard warnings, whether it is rockfall, soil or water related.

Lund also advises home buyers and developers to be do their research and take the hazard warnings seriously.

"(The important thing to know) about rockfall hazard is it's not random. It doesn't just happen any place," Lund said. "We can identify where it happens. We can map it. ...It's not a random act of God. We can tell where it's going to happen. We just can't tell you when it's going to happen."

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