ROCK SPRINGS -- State officials will unveil the initial findings from their investigative drilling in a neighborhood beset by damage during an ill-fated ground-pounding subsidence project in 2007 at a meeting Tuesday night in Rock Springs.

Wyoming Abandoned Mine Land Division officials said the most recent investigative drilling at various locations in the neighborhood aims to provide more information about what's actually happening in the abandoned underground mine shafts and voids.

Officials said the information will then be used to plot the course and method for future mitigation and reclamation efforts in the neighborhood.

State engineers have been conducting investigative drilling in the "Tree Street" area of downtown Rock Springs to try and determine exactly what's happening within the numerous mine voids that lay scattered beneath the neighborhood.

Rock Springs was built around the coal mines, which were first developed in the 1860s to supply coal to the Union Pacific Railroad.

More than 100 million tons of coal was mined over the next century from the Rock Springs field. One result is that many, many miles of underground mine tunnels traverse underneath many homes in the city.

More than a dozen homes were damaged in the neighborhood during the controversial ground-pounding project conducted two years ago that aimed to free up vacant lands within Rock Springs for much-needed housing development.

State officials have been negotiating with residents for more than a year over the settlement offers to repair damage from the project.

In the meantime, the AML has been conducting subsurface investigative drilling -- which began in the fall of 2008 -- in the neighborhood to determine if any mitigation measures are required, said AML program manager Bill Locke.

Drilling resumed Sept. 21 to gather additional data to supplement the data previously collected, he said.

Two drilling rigs are being employed along with geophysical evaluations of underground mine workings as part of the process.

The drilling will continue through December, weather permitting, and is tentatively scheduled to resume in March or April, according to plans.

"We got the results from the first drilling in that area that was done a little over a year ago ... we looked at what we had and we decided there was some more information we needed in certain places," Locke said. "So we went back in last month to fill in some holes in the data and to better define the conditions (underground).

"We're getting a complicated picture [of what's happening underground] and that's why we're back there doing this additional work," he added. "We're not finding exactly what we think we should be finding and that should be pretty evident with the information we're putting out Tuesday night."

New inspections

In mid-July 2007, contractors for the AML began work on a subsidence project known locally as the "Big Drop."

City officials had selected a 61-acre site called Tract H, which is located along Blair Avenue and the city's Belt Loop, for the planned $2.4 million project.

A key component of the project was the use of a pilot technique known as dynamic compaction.

The process involved dropping 25-ton and 35-ton weights to collapse underground mine voids within the tract, which sits over the old Excelsior/John Park coal mine first leased by the Union Pacific Coal Co. in 1911.

For three weeks, beginning July 17, 2007, cranes pounded the ground using dynamic compaction, dropping the weights more than 2,200 times before homeowner complaints halted the project.

Residents said the shock waves from the ground pounding shook houses, accelerated ongoing subsidence and severely damaged most homes in the area from the foundation up.

The state sent in engineers to asses 19 damage claims filed by homeowners under an initial settlement process established by the AML Division in 2008.

The state followed that up with settlement offers in December based on the engineer's reports. Four homeowners accepted the state's offers, but those that didn't contended the offers won't adequately compensate them for the needed repair work.

At the behest of state lawmakers, the agency agreed to redo the engineering inspections of the damaged homes, with an eye toward making new compensation offers to homeowners at a later date.

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