Study: Up to 144 years for aquifers to recover from methane gas development
The coal-bed methane gas boom that dotted northeast Wyoming with rigs and workers in the 2000s and left a legacy of bankruptcies and orphaned wells will also have lingering impacts on groundwater for up to 144 years, according to a new study by the Wyoming State Geological Survey.
Some sandstone aquifers in the Powder River Basin have declined by more than 100 feet due to the industry’s preferred method of pumping large volumes of water from coal seams to release the microbial-formed coal-bed methane gas, according the study, “Groundwater Level Recovery in the Sandstones of the Lower Tertiary Aquifer System of the Powder River Basin, Wyoming.”
The industry has pumped about 1 million acre-feet of water from coal seams since 2001 and discharged it onto the surface, partially depleting coal aquifers as well as associated sandstone aquifers. That’s enough water to fill Alcova Reservoir to maximum capacity more than five times.
“The calculated times of recovery, which vary from 20-144 years with a mean value of 52 years, probably represent best-case estimates because the calculations assume that environmental and hydrological conditions will largely remain unchanged from those of the last decade,” the study states.
“Furthermore,” the study continues, “slowing recovery rates commonly observed in some coal seam aquifers may impede the return to predevelopment water levels in the proximal sandstones.”
The most severely drawn down aquifers are within 20 miles of the Powder River, both north and south of Interstate 90, study co-author Karl Taboga said. That’s also the area where much of the remaining active coal-bed methane wells are located. While the geographic coverage of the monitoring wells used to measure water tables is limited, it’s believed the industry’s impact to aquifers elsewhere in the Powder River Basin is less severe.
“It appears to be localized,” Taboga said. “In a couple of cases, a little farther east in the Powder River, you may have a site that has a significant groundwater decline, but five or six miles away you have another site where you’re not seeing a significant decline.”
Ongoing groundwater monitoring in the Powder River Basin provides “a unique opportunity to study long-term groundwater changes,” State Geologist and WSGA Director Erin Campbell said in a press statement. “Understanding how subsurface systems relate to groundwater recovery allow us to best plan future development.”
But there are perhaps even more critical lessons to learn, according to longtime critics of the industry’s dewatering practice.
“The big question is: Will we learn the lesson that we live in a high desert and pumping and dumping and wasting water is the height of greed and ignorance?” the Powder River Basin Resource Council’s former Executive Director Jill Morrison said.
The massive dewatering of groundwater resources has been a point of contention since the beginning of the coal-bed methane gas play in the Powder River Basin in the mid-1990s. In some cases, it sapped water from wells used for livestock and drinking water for homes. While the practice of discharging the water on the surface provided new stock watering ponds for ranchers, it also flooded critical grazing areas and loaded the surface with salts, wreaking havoc on native grasses.
The Sheridan-based landowner advocacy group Powder River Basin Resource Council pressured the state to minimize pumping groundwater and discharging it on the surface. Instead, it urged the state to insist on forcing operators to reinject the water “in a staged fashion.”
But the state didn’t take any actions to limit groundwater pumping and surface discharge until 2007 as the development began to decline.
“These aquifers took eons to establish and [coal-bed methane] development has significantly dewatered them in less than two decades,” Morrison said Wednesday, adding that she is “not at all surprised” by the report’s findings. “You can’t pump this gigantic volume of water out of aquifers that took eons to be created, and then expect that it’s going to regenerate.”
The diminished aquifers and long-term recovery rates represent potentially higher costs for rural landowners and agricultural operations to access groundwater, as well as municipalities that might rely on groundwater resources in the future, Morrison said.
Many in the Powder River Basin have already felt those types of impacts, Morrison added.
“The state said industry is responsible and they just have to drill you another water well that’s deeper,” Morrison said. “But that didn’t solve the problem because that [deeper] water isn’t as good, it costs more to pump and they didn’t pay for the extra electricity charges.”
For years, hydrologists have speculated at the potential rate that both coal and sandstone aquifers might replenish. Early estimates included a rate of 1 inch per year, Morrison said. The new WSGS study estimates a faster rate and notes that recovery rates will vary widely depending on geology.
“Typically, groundwater levels in the affected sandstone aquifers briefly rise by several feet for a few months after [coal-bed methane gas] production ceases,” according to the study. “But this rapid recovery frequently decreases to one foot or less annually after a year or two.”
Climate change may also play a significant role in the rate of aquifer recovery in the Powder River Basin.
The WSGS study notes that its estimated recovery rates “represent best-case estimates because the calculations assume that environmental and hydrological conditions will largely remain unchanged from those of the last decade.”
But Wyoming’s precipitation and snowmelt dynamics are quickly changing due to human-caused climate change, according to National Oceanic and Atmospheric Administration data. While much of Wyoming could see more overall precipitation, less of it will come in the form of snow that drives annual springtime melt.
However, since 2000, the Powder and Tongue River Basins have experienced their longest and deepest droughts compared to the last 100 years, based on the Palmer Drought Severity Index, University of Wyoming Department of Geology and Geophysics professor J.J. Shinker said.
“The increase in temperatures coincides with prolonged and deepening regional drought conditions and the trend of increasing temperatures (globally and regionally) is likely to continue well into the projected recovery timeframe,” Shinker told WyoFile via email.
Wyoming’s evolving climate conditions make it extremely difficult to predict aquifer recharge cycles, Shinker said.