Water collecting under the asphalt on Main Street is to blame for the second sinkhole in three years on the old road, said LaRon Garrett, Payson's public works engineer.
Estimating costs at about $1,000 to $1,500, Garrett listed poor soil compaction as the main cause for the 2 1/2-foot deep hole, discovered earlier in the week in the center of the road just in front of Peggy's Payson Place.
Repair work started Wednesday. Payson public works employees cut an old section of road out, repaired a sewer pipe affected by the sinkhole and put a concrete slurry mix in to fill the hole.
"That will make for less of a chance for this happening there," Garrett said.
The sewer line was put in about 3 1/2 years ago by the Northern Gila County Sanitary District, and while the district provides the town a two-year warranty, Garrett said it is difficult to prevent sinkholes permanently.
"There was an old sewer line in a trench and the dirt settled under the asphalt and finally broke through the surface," Garrett said. "In an old trench like that if you don't get real good compaction, over time it gets wet, the soil settles and it gets those voids," Garrett said.
"A compaction test is only good for that exact point you take it and it can be different five feet away. You always hope the compaction is uniform and every so often you find a spot that wasn't."
It is also more difficult to compact around sewers and utilities.
"You don't have the open trench to compact in. You have to work around all these other lines and it makes it a lot harder," he added.
Sinkholes are similar to potholes in that the ground gets soft and wet and moves away from the asphalt, Garrett said.
"Anytime we have a road failure like that, it is serious," he said. "We had one similar to this further west on Main Street a few years ago, but it is very rare to have something like this show up."
Crews should be out of the roadway by Friday, Garrett said.