Contamination Risks Associated with In situ-Recovery Mining for Uranium

Authors:

Falina Foroughirad, Geoscience

Ruth Russell, Natural Resource Conservation

Thomas Meyers, Building Construction Technology

 

During the Cold War, uranium mining in the United States took off as an industry to keep up with the Soviet Union in the nuclear arms race. One of the richest uranium deposits in the US lies beneath the Navajo Nation. The Environmental Protection Agency (2015) estimates that from 1944 to 1986, nearly 30 million tons of uranium ore was extracted from Navajo lands under leases with the Navajo Nation.  Many of the Navajo tribe members secured positions as miners, working in close proximity to radioactive material that was later discovered to be the cause of high rates of lung and bone cancer. Despite the fact that radon gas inhalation was proven to be statistically correlated with lung cancer, legislation failed to protect the Navajo tribe from the lasting effects of mining. Mine tailings of ore residue were scattered throughout the land and repurposed for local infrastructure, and the groundwater was contaminated without any effort towards complete remediation until 2007. At current, the EPA estimates that 30% of all Navajo people still lack access to uncontaminated drinking water and more than 500 abandoned uranium mines shafts are now estimated to lie on Navajo land (EPA, 2015).  Problems regarding uranium contamination include complications during mining that can result in leaks or improper waste disposal, and the uncertainty of the uranium mine stability after they have been closed. Stopping contamination is important to protect people like the Navajo tribe members who have been exposed to uranium mining’s negative impacts. Increasing monitoring of mines after closing is a critical step in maintaining access to clean drinking water.

Navajo tribe members were provided with jobs at the uranium mines that were on their land, but ended up unknowingly working with radioactive material known to cause cancer. #MoreMonitoringMining

The purpose of mining for uranium is almost exclusively to run nuclear power plants, which is considered a cleaner alternative to coal plants, as it eliminates greenhouse gas emissions.  The uranium mining industry has declined since 1980, and prices have slumped in competition with the foreign market. The mining industry and its supporters argue that opening up more land to mining activity will help the US reintegrate into the uranium market, thus making the US more energy independent. The decision to open more land to mining activity has resurrected a long-standing debate on whether or not uranium mining is worth the environmental impacts that accompany it. Parties that oppose the decision to open up more land argue that doing so will have a negative effect on drinking water quality (World Nuclear Association, 2016).  

Significant improvements in the uranium mining process has negated many of the risks associated with conventional mining, such as lung cancer caused by gamma ray exposure from uranium decay products, like Radon gas. However, this is not to say that modern uranium mining, or in-situ recovery (ISR), does not come without risks. The most relevant environmental risk associated with ISR is the contamination of groundwater. During ISR, a solution is injected into an aquifer (closed area that holds water) to extract uranium from the underlying rock, which is then brought to the surface to be processed. This technique intentionally contaminates the aquifer, but is immediately remediated by either flushing out the system with clean water or treating it via reverse osmosis, a pressurized filtering process (World Nuclear Association, 2017). After remediation, the mine is monitored until considered stable. It is important to monitor the groundwater because if it becomes contaminated, there is then a risk of polluted drinking water, which can negatively impact an entire community, such as the Navajo tribe.

In October 2015, the EPA proposed that uranium mines be monitored for 30 years and include the observation of other constituents that mobilize during mining, including arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver, nitrate (as nitrogen), molybdenum, and radium. After two years of negotiations with stakeholders and the appointment of Scott Pruitt to head the EPA, the original recommendation was retracted and shortened to 6 years, cutting the amount of constituents to be monitored by 50% (EPA, 2015). The EPA originally proposed a 30 year plan because according to geological monitoring of the conditions of the groundwater near ISR mines, it takes this long to determine if the conditions around the mining site are stable and then to regulate the problems if there are any. After 30 years of monitoring groundwater stability, the mine is considered to be permanently stable and monitoring no longer needs to occur (EPA, 2015). The EPA also argued that ISL is still a relatively new practice at less than 30 years old and because of this the contamination risks are understudied and research is underfunded (Fonseca, 2018). Research projects with the objective of efficiently stabilizing uranium mines have showed some promising results, but without funding, excessive monitoring remains the only other alternative in keeping contamination risks minimal (United States Geological Survey, 2014).

Longer periods of monitoring are also necessary because groundwater chemistry can change after a mining site is closed. Jemison, Johnson, Shiel, and Lundstrom (2016) state that natural environmental processes, such as the chemical evolution of groundwater, can produce a nuclear field shift effect, where previous fractionation ratios, or the measured, expire. Remaining uranium in the ground can remobilize, resulting in a “rebound effect”, which temporarily increases the amount of uranium released in a short burst, risking further contamination of the groundwater. The chemical profile of the aquifer, or the amount of uranium and other trace elements, can be changed naturally by fluctuations in pH or temperature within the aquifer. Excess acidity or alkalinity can catalyze the rate at which uranium is removed from the rock surrounding the aquifer (Jemison, Johnson, Shiel, & Lundstrom, 2016). In other words, residual metals are most stable under normal pH of water, and are released abruptly due to disturbances in system caused by the mining solution or natural fluctuations.  This occurred at the Smith-Highland Ranch in Wyoming, where post mining uranium levels were 5.61 times the amount measured before mining (Ruedig & Johnson, 2015).

Because open-pit mining has contaminated aquifers in the past, there is the possibility that ISR mining will as well, especially since it is interacting with the aquifer directly. If pressure is not stabilized during mining, the soluble uranium in the confined aquifer can travel up the borehole into the overlaying unconfined aquifer, contaminating the groundwater (Way, 2008). This process is best explained by the fluid dynamic properties of water, where water will always seek the lowest pressure, rather than the lowest elevation, causing it to travel in a vertical direction, perpendicular to the ground. This type of risk is especially alarming to communities such as the Navajo tribe, because contaminants are released in large amounts into the overlying unconfined aquifer. The aquifer interacts with the surface water immediately due to the lack of an impermeable layer. It is inevitable that the host aquifer will never be 100% restored to pre-mining conditions, as mobile residual uranium is often left underground after mining has ceased (EPA, 2015). In another study done at the Smith-Highland Ranch in Wyoming, one well had uranium present in a concentration of 1920 mg/L, where the average for post mining conditions is approximately 8 mg/L (Gallegos et. al 2015). This means that the amount of uranium found was 240 times the amount it should have been following remediation. The risk of contaminating surface water exacerbates the issue of having clean drinking water, as not all drinking water supplies come from artesian wells with confined aquifers.

In addition, by-products from ISR uranium mining such as lead, thorium, polonium, and arsenic are trace metals that pose risks equivalent to that of uranium. At the Maluu Suu uranium mine in Kyrgyzstan, arsenic was detected at 1600 μg/L, which is 160 times greater than the WHO guideline of 10 ug/L (Corcho Alvarado, Balsiger, Rollin, Jakob, & Burger, 2014). However, in a processing and tailings management facility India, the uranium levels in the groundwater sources in the vicinity of the tailings pond are very similar to the regional average of 3.6 μg/L, respectively, indicating that there is no groundwater migration of radioactive material (Tripathi, Sahoo, Jha, Khan, & Puranik, 2008). This proves that depending on the mine, groundwater can be impacted at different severities. Lengthy monitoring can be used to discover contamination before it is too late, so the groundwater can be recovered to prevent polluted drinking water.

In the EPA’s 2015 proposal, they decided that in order to negate the contamination and stop it from recurring, ISR facilities would have to have 9.5 years of monitoring if the conditions were stable, and 32.5 more years of monitoring if there was previos long term monitoring for 30 years. The average cost of 30 years of monitoring for groundwater stability is $13.5 million, or approximately $300,000 for each mine (EPA, 2015). Compared to the cost of remediation, this is very low, at almost a one thousandth of the cost depending on the size of the breach. A report published by the US Energy Association estimates that the cost to remediate an open-pit mine ranges from 150 to 250 million, and they state they are unable to assess the actual cost of remediating groundwater, but warn that it is “much higher” than that of the conventional mining sites. The Midnite mine in eastern Washington, for example, has required $195 million in clean up costs over a 140 year long period (US Department of Energy, 2014). Although this proposal did not go through and the required monitoring time was significantly decreased, it shows what the amount of monitoring time for ISR mines should be in order to stop contamination. According to a report from the Radiation Protection Division of the EPA, if ISR wells were monitored more often, contamination would be detected quicker and the groundwater would be cleaner. It is necessary to have a restored groundwater baseline that is at a steady state and does deteriorate over time. Monitoring the groundwater near ISR sites helps recover the ecosystem without posing a threat. Monitoring groundwater can help detect changes in the composition of the groundwater during ISR mining. Data collected from the wells is also used to ensure the decontamination of the aquifers. Without this data, it is unknown as to whether the aquifers need to be further restored (Radiation Protection Division, 2014).  

A reason why we are trying to make such a change in the moderating of the uranium mining fields is because of the positive impact it will have on the the ecosystem and drinking water.  In order to help make progress and changes the author Carvalho, talks about how programs are changing the way they get the data. He talks about how there are field surveys taken regularly now and have to be given to the government.  The results are also given out to the public and people can see what the field surveys are made off and can have an input. This is all too hopefully improve the the safety to the population and have a better impact on the ecosystem (Carvalho, 2013).  With more data and better evidence to what the uranium mining is doing it will help stop the pollution to getting to the nearby ecosystems and drinking water. In addition, monitoring programs are able to find out if the site has leakage and can give baseline data for the site.  These monitoring programs also place monitoring wells up to 500 feet outside of the ISL mining site zone, to test for contamination and protect the surrounding ecosystems (Way, 2008). In another study by the National Resource Council talks how the long term of uranium mining is foggy because of the short amount of data that the scientist have.  The council says that data is limited data on the long term effects. They do mention though that their has been improvements in the recent years and that has helped them figure out what the problem is (National Resource Council, 2012).  The national resource council explains with the increase of data on the short term of mining it has allowed them to improve the decrease of pollution caused by uranium mining and how it’s hard to do to look at long term effects due to the lack of data.  With the change of moderately monitoring of 6 years now the scientist will be able to have more reliable data.

Although ISR uranium mines are now being moderately monitored, the monitoring period is only 6 years, instead of the originally suggested 30 years by the EPA (EPA, 2015). ISR uranium mines need to be further monitored for a number of reasons. Uranium mining contaminated the surrounding groundwater which negatively impacts the ecosystem and drinking water.  Trace metals are leached into the groundwater from the mining and this contaminated groundwater is connected to the aquifers that connect to nearby ponds and lakes. If contamination ensues, it can take up to 30 plus years for groundwater to regenerate, due to the relatively slow velocities of water beneath the surface. If there is further monitoring for longer periods of time these negative environmental impacts can be lessened and reversed more quickly. If the wells are monitored more frequently, contamination will be discovered quicker and is able to then be taken care of (Radiation Protection Division, 2014). It is also important to monitor for longer periods of time because groundwater chemistry changes even after a mine is closed and this can only be detected if it is being continuously monitored (Ruedig & Johnson, 2015).

 

References:

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Environmental, Human Health and Safety, and Regulatory Aspects of Uranium Mining and Processing in Virginia. Washington, DC: The National Academies Press. https://doi.org/10.17226/13266.

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Evan

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