Water study finds naturally occurring methane south of Silt
New study results help demonstrate the role that naturally occurring methane appears to be playing in the substance’s presence in domestic groundwater south of Silt.
That’s according to Geoffrey Thyne, a geologist who previously has voiced concern about the degree to which natural gas development also may be contributing to the problem.
The consulting firm Tetra Tech has completed the third phase of a study the county has been conducting south of Silt to better understand the hydrology of the area and possible impacts of oil and gas development. It was undertaken after gas from a faulty Encana well surfaced in 2004 in West Divide Creek, amid concerns that heavy geological faulting in the area could lead to shallow groundwater being contaminated by drilling and hydraulic fracturing in deeper formations.
Methane has been detected in many domestic water wells south of Silt, and Thyne, who long has served as a consultant to the county, previously has argued that drilling in the area appears to be contributing to the problem.
The latest Garfield study made use of three pairs of monitoring wells, each pair drilled at roughly 400- and 600-foot depths into the Wasatch geological formation. The Wasatch surfaces south of Silt and lies above the Mesaverde formation, which energy companies have been targeting for drilling in the area.
Methane was found in all of the wells in the latest study. However, it determined that the gas in the shallower wells appeared to be of a biogenic source, meaning it’s a result of microbial activity. Methane in the deeper wells appears to be thermogenic, meaning it was created through geologic processes involving heat and pressure.
Thermogenic gas is the kind being targeted by energy companies. But Thyne, who provided the county with a technical review of the latest study results, said the monitoring well test locations are believed to have little or no connection to surrounding aquifers. That means they should be isolated from possible impacts of oil and gas development.
As a result, the study provides valuable information about what natural background levels of gas in the Wasatch formation look like, including thermogenic gas.
“This is kind of what the natural background is. We do have some naturally occurring methane in the background,” Thyne said.
Thyne also previously had theorized that some biogenic gas showing up in domestic groundwater had a thermogenic origin. But given the study results, “it looks like it’s not (thermogenic). It looks like it’s naturally occurring.
“… It’s now not a surprise to me that we occasionally see some biogenic methane, and we know it’s biogenic,” he said.
Thyne still is concerned that some domestic water wells may be impacted by gas development. But he said he’ll be able to use the new information, including the chemical fingerprint of natural, background gas, to go back and re-evaluate his past analysis, and possibly remove some wells from the list about which he has concerns.
He said the latest results should provide “big relief” to people concerned about methane in water.
“Hopefully people will be able to go ‘ahh, good,’” in learning about the natural explanation for at least some of the Wasatch-level methane, he said.
The monitoring wells were drilled near the area of the West Divide seep.
Thyne said they also help indicate the limits of the extent of that contamination by clarifying what levels of naturally occurring methane exist in the area.
“We now know that West Divide is a very well-contained, very distinct or small leak. We really know that now — that’s what we got out of this study,” he said.
He said it indicates the methane impact at the nearby property of Lisa Bracken “was relatively minor.”
Bracken long has been concerned about the extent of the West Divide seep and other possible drilling-related contamination in the area, including on her property. She said even 600-foot-deep monitoring wells are shallow compared to the formations companies are drilling in, and she believes faulting and high pressures are resulting in contamination from those formations.
She’s looking forward to seeing the latest study results.
“As long as the raw data has not been manipulated and excised in any way, then there’s an opportunity for independent review,” she said.
She said she also believes the entire issue needs a continued, more thorough investigation.
No drinking water standards exist for methane, although it can pose a risk in domestic water because of its ability to accumulate in enclosed areas and explode.
The study also found benzene, a carcinogen, in several wells. Just one sample exceeded the drinking water standard of 5 parts per billion, being measured at 5.3 ppb. The study theorized that the presence of low benzene levels in several wells suggests benzene may be present naturally in the Wasatch formation.
The study results will be presented Tuesday to Garfield County commissioners.
“At the county we look forward to people taking the time to dive into the study results and the data and to see what they can learn about the area that they didn’t know before,” said the county’s oil and gas liaison, Kirby Wynn.
“… There’s going to be a variety of opinions that will come out from the data set,” he said.