by Amber Reimondo, Energy Director
In 1986, the U.S. Forest Service approved a plan to operate a private uranium mine on the Kaibab National Forest, near Grand Canyon National Park. Based on the science available at the time, the Forest Service determined Canyon Mine (which would later be renamed Pinyon Plain Mine) did not threaten groundwater in the Grand Canyon region, including the deep Redwall-Muav Aquifer that feeds springs in the Grand Canyon which flow into the Colorado River.
In 2012, the Forest Service reviewed its 1986 findings and determined there was no reason to reevaluate the potential effects of uranium mining at Canyon Mine, reasoning that the science and the facts on the ground had not changed.
But in the intervening decade, things have changed. In 2016, miners developing the mine hit groundwater and the company has been pumping it out of the mine shaft ever since.
The science the mine’s approval was based on nearly four decades ago is outdated and needs review. Arizona’s attorney general has called for a new supplement to the outdated 1986 environmental impact statement that originally evaluated the risks the mine poses to groundwater.
Scientists have learned a lot about groundwater in the Grand Canyon region since 2012. Studies indicate that Canyon Mine, renamed Pinyon Plain Mine in 2020, potentially puts groundwater and associated springs and ecosystems in Grand Canyon National Park at risk. It’s time for the Forest Service to take a hard look at the mine and consider the science.
Since 2016, more than 66 million gallons of water have had to be pumped out of the mine shaft .
We recently caught up with groundwater scientists Dr. Laura Crossey, Dr. Karl Karlstrom, and Dr. David Kreamer, who study groundwater in the Grand Canyon region. We asked them about some of the Forest Service’s scientific conclusions from 1986 and 2012 considering the science available today.
1986 and 2012 claims: The Redwall-Muav Aquifer is at least 2,500 feet below the surface of the mine.
The deep Redwall-Muav Aquifer feeds many springs in the Grand Canyon. AMY S. MARTIN
Crossey, Karlstrom, and Kreamer: Actually the mine is permitted to allow operation just a couple of hundred feet above the deeper Redwall-Muav Aquifer. Faults and fractures are known to connect the upper C Aquifer and the lower R-M Aquifer — although we still don’t know how well connected the aquifers are at a given site, including the Pinyon Plain Mine site, and this is the key question for the new environmental impact statement (EIS).
Additionally, other nearby breccia pipes next to the Pinyon Plain Mine have not been tested for vertical hydraulic conductivity. Such connections are not restricted to be strictly vertical in nature. Many recent studies demonstrate simultaneous downward and lateral (sideways) migration in short (months to years) timeframes across thousands of feet vertically and tens of kilometers laterally.
1986 and 2012 claims: Due to parallel-bedded layer cake stratigraphy, groundwater flow in the local perched aquifers should be to the southwest toward Havasu Drainage and Cataract Creek.
Crossey, Karlstrom, and Kreamer: The term 'perched aquifer' is often used to refer to the C aquifer, but we now know it to be incorrect at worst, and incomplete at best. Stable isotopic values for the C and R-M aquifers overlap in values on both rims of Grand Canyon showing that water moves down across the bedding from the C to R-M aquifers along faults and fractures (gravity).
This was proven for the North Rim by the national park’s dye tracer study, but the rate of downward flow at the Pinyon Plain Mine site is not known and needs to be studied. This site is being massively perturbed by pumping of the C Aquifer, creating a cone of depression and additional water quantity concerns such that now is the time to quantify the rate of downward flow in a new EIS study.
1986 and 2012 claims: The C Aquifer is generally not saturated as far west as the mine and thus should be unaffected.
The mine mists water into the air to speed up evaporation. BLAKE MICCORD
Crossey, Karlstrom, and Kreamer: This assertion has now been proven to be untrue. The mine (and many hydrologists) were surprised when the mine began taking on water in 2013 and more significantly in 2016. The mine continues to have to pump 8-9 million gallons per year to be able to dewater the shaft and continue mine operations. This is drawing down all four of the shallow observation wells around the mine site, creating a cone of depression which proves both lateral connectivity and vertical fluid connectivity across the Hermit Shale, which was thought to be the confining layer below the upper aquifer.
The important long-term question that needs answering now is the extent to which this vertical flow is following natural faults and fractures versus following the 'Swiss cheese' of exploratory drill holes (more than 17.5 linear miles) that perforate the mine area, with some extending from the surface to the lower Redwall-Muav Aquifer. In either case, for a future remediation strategy, a new EIS that recognizes well-established science is needed to figure out the direction of flow and the fast-versus-slow water pathways in the C Aquifer and between the C Aquifer and the lower R-M Aquifer.
Our figures of the mine show that saturated zones likely exist in the upper Supai Group as well as the Coconino Sandstone, and the present configuration of four wells drilled only to the top of the Hermit Formation, and one deep well into the R-M Aquifer are inadequate to establish the direction of horizonal flow in either aquifer, the extent of saturated zones between the aquifers, and the vertical pathways (faults, fractures, the breccia pipe itself) that likely convey water between them. Bills et al. (2007) showed that the C Aquifer includes the upper five formations, that all can be variably saturated, not just the Coconino Sandstone.
1986 and 2012 claims: Perched zones are generally small and unsuitable as long-term water supplies.
Crossey, Karlstrom, and Kreamer: This has been disproven by the mine itself as they have had to pump millions of gallons of water from the main shaft for the past eight years.
Additional water is pumped from interception rings in the upper aquifer and used in part for surface dust control. If the groundwater the mine struck was truly insignificant, the flow would have stopped after a short period of pumping. The mine is presently dewatering an important regional aquifer with no sign of stopping. It is not a question of if, it is a question of when and in which directions this dewatering may affect Grand Canyon springs and nearby wells.
Similarly, we do not know the level of contamination this is causing in the shallow or deep groundwater and this needs monitoring. The timescale of water transport is now known to involve both fast and slow pathways, so the question of long-term versus short-term effects needs reevaluation.
1986 and 2012 claims: The single monitoring well at the mine site should be adequate for evaluating any potential perched aquifer impacts.
Crossey, Karlstrom, and Kreamer: This is incorrect. It has been long known that a minimum of three wells, strategically placed in even the simplest groundwater system, are needed to determine the flow direction in each aquifer. The deeper R-M aquifer is in a very complex (Karst) system and more than the minimum may be needed.
In his book, Notable Springs of the United States (2024), Dr. Neven Kresic of the Karst Waters Institute said of similar claims by the Arizona Department of Environmental Quality (ADEQ) seeking to justify only a single deep well, 'Based on my professional judgment, this statement by ADEQ is nonsensical from a hydrogeologic standpoint and contrary to the entire professional and academic practice of groundwater science and engineering in any porous media and type of aquifer, not just in karst.'
The four existing wells in the shallow aquifer are too shallow to evaluate at the level of the upper ore body. There are no data available to evaluate the flow direction and degree of contamination in the units of the lower Supai Group, above which the C-Aquifer is asserted to be perched. To say it another way, the mine has no data or comprehensive fracture analysis to show any barrier to vertical fluid movement between the C and R-M aquifers. The one well in the R-M Aquifer is not adequate to determine flow direction and degree of any contamination in the R-M Aquifer.
The very complex passages and compartmentalization known to occur in the R-M karst aquifer is such that more frequent sampling of water level and changes in contamination of this one hole is needed now (currently only annual sample analysis is occurring), as well as a new plan to drill at least three to four more deep wells to establish a valid monitoring program for future remediation.
In short, the science is clear. Things have changed since 2012. It’s time to supplement the 1986 environmental review and take a hard look at what scientists have learned in the nearly 40 years since the Canyon Mine was first approved.
Groundwater pumping at a uranium mine near the Grand Canyon will affect the canyon's springs, scientists says.
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Arizona Governor Katie Hobbs is the latest elected official to call for an environmental review of Pinyon Plain uranium mine.
Read MoreSign the petition to oppose Canyon uranium mine (aka Pinyon Plain Mine) Sign now
