An in situ leaching mine in Goliad County, Texas.
Metal ore mining is generally considered to have a heavy environmental footprint. Visions of landscapes scarred by huge open pits of concentric spiraling roads carrying truckloads of ore, acres of mine tailings and towering waste piles come to mind. Or one thinks of men in deep underground shafts and tunnels, working in less than ideal conditions, living in houses covered with black dust and suffering an inevitably untimely death.
A third mining technique, known as “in situ leaching,” has been heralded as environmentally friendly, because it is less obvious while in progress and leaves an area almost the same as before mining operations began.
In situ leaching mining may not despoil the landscape, but it is not necessarily benign. If a body of ore is physically linked or associated with an aquifer containing groundwater necessary for human and/or animal usage, there is a risk of contamination. The uranium deposits along the Texas gulf coast are a case in point.
In situ leaching recovery mines consist of a series of injection wells and recovery wells. A chemical solvent is pumped down the injection well, dissolving the ore in situ, and then the ore solution is pumped out through the recovery wells for processing. This type of mining is cheap, efficient in recovery of metals from low-grade ores, and is completely underground, hidden from public view. After the mine is exhausted, the wells are capped and its former presence can be made nearly invisible.
The uranium found under the Texas coastal plain originated through intense volcanic activity in the Trans-Pecos region 48 million years ago. Uranium, dissolved in oxygen-rich groundwater, precipitated in chemically reducing zones along natural faults in sandy coastal aquifers. As long as the ore zone remains in an oxygen-free condition, the uranium and its decomposition product, radium, remain insoluble and do not travel with the flowing associated groundwater, which is suitable for drinking.
The injection of oxygenated water for in situ mining dissolves the ore, releasing uranium and radium into the groundwater. Because of the mobility from the associated aquifer, the recovery wells may not trap all of the liberated uranium and radium, allowing them to migrate through the aquifer and into adjacent farmhouse and livestock wells.
It is my conclusion that allowing in situ uranium mining using existing standard protocol for obtaining drilling permits is not in the public’s interest. Before any mining can begin, the proposed areas to be mined must be exempted from being an underground source of drinking water. However, because the water needed to drill test wells liberates these two radioactive elements, it is impossible to even establish a before-mining concentration level for groundwater uranium and radium. Thus, a mining company can never know what uranium and radium concentrations must be restored after mining to re-establish original groundwater conditions.
As a result, the water within the proposed production zone may very well be of drinking water quality prior to exploration activities, even though it erroneously tests high in uranium or radium. Issuing a mining permit on the basis of falsely elevated baseline concentrations of uranium and radium would exempt a source of drinking water and would lose any use of this water indefinitely.
I believe that better and less-invasive methods can be developed that will ensure accurate baseline values of uranium and radium concentrations in the groundwater of the ore-body containing aquifer and that will assure that the mining area aquifer is restored to its correct original condition.
Read more about issues of regulating in situ leaching uranium mining in “Uranium Mining in Texas: Why Is It Done That Way?” (PDF) by Ronald Sass.
Ronald L. Sass, Ph.D., is the fellow in global climate change at the Baker Institute and the Harry C. and Olga K. Wiess Professor of Natural Sciences emeritus at Rice University. He has consulted for the Environmental Protection Agency and advised the United Nations Development Programme Interregional Research Program on methane emission from rice fields in Asia. Sass has also received the Rice University Award of Highest Merit, the Rice University Alumni Association Meritorious Service Award and the Rice University Alumni Association Gold Medal of Honor.