ROCK SPRINGS - State Abandoned Mine Lands officials began a more comprehensive sampling effort of Becky Kelley's beleaguered home on Wednesday in an effort to determine the source of leaking deadly mine gas that forced evacuation last week.

The agency is now testing for concentrations of carbon monoxide, carbon dioxide, methane and hydrogen sulfide, AML officials said in a release Wednesday.

Officials said engineers and consultants continue to investigate the presence of gases in other nearby homes on Ash Street that have been damaged by a nearby mine subsidence project that began in mid-July.

State and city officials said they expect to continue with the subsidence project, which aims to free up much-needed land within the city for housing development. They're evaluating how to move forward without using a ground-pounding technique thought by some to have caused the damage.

The deadly hydrogen sulfide gas that has been leaking from old, underground coal mines in Rock Springs for about a week caused AML officials to arrange for alternative housing for some Ash Street residents last week.

Kelley, whose home seems to have the highest concentrations of what is known as black mine gas, has been living in a local motel for a week. She has been experiencing symptoms of exposure to hydrogen sulfide gas, according to her doctors.

Technical consultants placed three gas monitors in Kelley's home and several other monitors in nearby residents' houses. On Tuesday, engineers were back to place the five additional monitors in Kelley's home.

Officials said results of the more intensive testing should be available Friday.

"These results are expected to accurately identify the presence and concentration of any sulfur compounds in both the crawl space under (Kelley's) home and the main floor, and will provide the department with information that will influence how it should proceed," DEQ spokesman Keith Guille said.

"We're going to find out for certain (about gas levels) because (the monitors) we've had in there now prior to this were measuring parts per million and the numbers have fluctuated at times … and so are kind of inconclusive," Guille said.

He said most of the samples have produced negative results, but there were a few that indicated low levels of hydrogen sulfide in three Ash Street homes that were evacuated.

"We want to find out what the issues are and get a sense of what kind of gas is there," Guille said. "And we're double-checking to make sure there are no other issues as well."

Kelley, the project's most vocal critic, said her house has suffered more than 80 cracks and other damage to her foundation, roof and driveway since the project began.

The ground pounding, or dynamic compaction, process has been used since the 1960s in areas such as Ohio, West Virginia, Virginia and other urban sites, mostly as a tool for compacting earth for the construction of building foundations, bridges and highways.

The process involves pounding the ground repeatedly by dropping 25-ton weights to collapse the old, underground coal mine voids.

For several weeks beginning July 17, Wyoming's AML division used the technique to collapse underground mine voids on a 61-acre tract of land near downtown Rock Springs. The site sits over the nearly 100-year-old Excelsior/John Park coal mine originally leased by the Union Pacific Coal Mine.

AML engineers dropped the weight more than 2,700 times before residents' complaints about structural damage to their homes halted work Aug. 6. A contentious town meeting Aug. 14 led AML directors to cancel the dynamic compaction portion of the project.

AML officials said the technique had never been used on this large a scale for mine reclamation. They touted the technique as a way to allow the agency to reduce subsidence risks more quickly and more economically than the state's traditional approach of injecting grout into underground mine voids in Rock Springs.

What's the cause?

Fred Coleman - owner of Coleman Construction Co., the Dillon, Mont.-based lead contractor on the project - said Wednesday he's not sure if the gas release was a result of the dynamic compaction.

"I can't say one way or another about what happened, because I don't really know … but there's some pretty good data saying nothing happened," Coleman said in a phone interview from the project site.

"But maybe there is a volcano under there and this (project) was like the straw that broke the camel's back," he said.

He said seismic data readings taken during the project's duration showed the vibrations were well within industry safety limits. Before the project began, workers placed numerous seismographs around the project site and within residential areas in the vicinity.

The monitors recorded "acceptable" vibrations (any number 2 or below) or damage-causing vibrations (over 2) that occurred while dropping the weights. Coleman said vibrations above 2 are considered strong enough to break sheetrock.

"The first drop we got a 2.6 (recording) in a location 100 feet from the pounder, then we dug a trench all the way around it, and that dropped (readings) to about a .6 from then on," he said.

The 61-acre dynamic compaction project was the first of several other planned mitigation projects in the area that had been slated for dynamic compaction, grouting and backfilling work.

Guille said the overall, 190-acre project to make lands available for housing development was "re-evaluated." He said at the request of Rock Springs officials, work will resume on the project in about a month.

"The city … has a strong desire to make these undesirable tracts available for development of affordable housing, and is therefore very supportive of this project moving forward now that more acceptable mitigation methods will be used," Rock Springs Mayor Tim Kaumo said in the release.

The agency plans to use only mass excavation and backfill techniques, which Guille said has proven successful in the Canyon View Estates area of Rock Springs.

AML officials said the agency intends to honor its commitment to pay for repairs to all houses suffering damage from mine subsidence, whether caused by the dynamic mine compaction or not.

Guille said the AML division is developing a process by which project-related damage claims can be filed by residents and processed by the agency.

Southwest Wyoming bureau reporter Jeff Gearino can be reached at 307-875-5359 or at gearino@tribcsp.com.