ROCK SPRINGS -- Workers successfully completed the "Big Lift" of the Pine Street home of Dennis and Karla McAffee, which was damaged from a controversial subsidence project two years ago known as the "Big Drop."

Wednesday's improvement project came with a heavy toll, however, as more damage appeared in the home while it was being re-leveled by a sophisticated hydraulic lift system.

Several large cracks appeared in the kitchen, living room and other areas of the home as a result of the stabilization effort, which took just a few hours. Some of the exterior brickwork was also damaged.

"It's totally overwhelming," a tearful Karla McAffee said while watching workers with the Utah-based contractor Atlas Piers conduct the lift.

"We've still go so much work ahead of us ... but at least it's safe and secure now," she said.

"That part of the house, as least as far as those piers go, are complete ... now we're going to have to do the rest of the house next year," she added. "I don't know if I want to go through all this again, but we will if we have to. We've got a ways to go, but we're definitely going to get there."

Atlas Piers, which specializes in the installation of foundation support systems, used a hydraulic system to raise the north, front end and the east side of the McAffee home to level the structure.

"It went about as smooth as we expected," Atlas Vice President Scott LeGrande said. "It's a really neat process, and it works really well."

Old coal mines

The repair project comes more than two years after the state's coal mine subsidence project was halted amid homeowners' complaints of damage in the city's downtown "Tree Street" neighborhood.

Many homes in Rock Springs were built around and on top of old coal mines, which were developed in the central Sweetwater County city in the 1860s to supply coal to the Union Pacific Railroad. As a result, many miles of underground mine tunnels traverse underneath many Rock Springs residences.

The Tree Street neighborhood sits over three different coal mines that lie at two different depths. The mines were all closed and abandoned in the 1920s.

Spurred by a long search for affordable housing, city officials selected an undeveloped tract of land in 2007 as the site of a $2.4 million subsidence project. The tract sits adjacent to the Tree Street area.

A key component of the project was the use of a pilot technique known as dynamic compaction. The process involved dropping 25- and 35-ton weights on a portion of the tract to collapse the underground mine voids.

For three unforgettable weeks beginning July 17, 2007, cranes dropped the weights more than 2,200 times before homeowners cried, "Enough!"

Tree Street residents said the shock waves from the ground pounding reverberated through the neighborhood, cracking foundations and driveways, opening sinkholes in yards, and causing cracks in walls and floors, among other damage.

The historic McAffee home -- built in the 1920s and then lovingly refurbished by the couple over the past decade -- received heavy damage. The house sits about three blocks from the dynamic compaction project site.

Shortly after the project was halted, state Abandoned Mine Lands Division officials pledged to pay for repairs to homes damaged by the dynamic compaction portion of the project.

The state assessed the damages under an initial settlement process established by the AML Division in 2008 and then made settlement offers to 19 homeowners.

Most homeowners rejected the state's offer, contending the proposed payments wouldn't adequately compensate them for the needed repair work. Attorneys for the residents and the state have been negotiating for months on a new agreement that would allow state engineers to reinspect the homes and make new settlement offers.

Part of the fix

McAffee said her family is paying for the project until an agreement can be reached with AML officials concerning payments for damages.

She said engineers were concerned about the structural safety of her damaged home and wanted to complete the project before the onset of winter.

The house was slumping on the east side fireplace wall, and a brick column holding up the northwest end had separated from the house.

Wednesday's Big Lift raised the front and side of the house several inches off the ground to make it more level, according to project foreman Sam Perry.

Workers dug out the driveway, front porch walkway and the concrete near the column last week. Holes were then drilled into the underlying rock formations and permanent, L-shaped manifold devices were attached to the bottom of the house.

Perry said 25-ton cylinder jacks were placed in the manifolds, linking them to the steel piers. A complex hydraulic system was then used to raise the structure.

The jacks were then left in place to permanently stabilize the structure. Workers began backfilling the site Wednesday afternoon, and McAffee said the driveway and walkway will be repaved later this year.

McAffee said contractors expect the house to keep settling over the next three weeks or so.

"We're going to see additional cracks and such from the lift," she said.

Contact southwest Wyoming bureau reporter Jeff Gearino at 307-875-5359 or gearino@tribcsp.com