Groundwater Remediation from Uranium Mining in New Mexico Jerry Schoeppner – New Mexico Environment Department he Grants uranium district in partially dewatered in order New Mexico northwestern New Mexico was to remove ore. Prior to the Ta prolific producer of uranium mid-1970s, water generated from the 1950s to the early 1980s. Most of during dewatering activities the uranium mining and milling activities was discharged to the surface occurred prior to the development of and allowed to flow into environmental laws and regulations natural water courses without Chaco Canyon aimed at protecting human health and the any treatment. These mine Nose Rock Churchrock— environment. As a result, conventional water flows were a significant Crownpoint Ambrosia Lake industry practices employed during this source of contamination of Marquez period caused extensive groundwater sediments, alluvial aquifers, Smith Lake Barnabe contamination throughout the area. and even deeper aquifers Montaño Grants Adequately addressing groundwater in areas of faulting. contamination has been complicated Laguna Albuquerque Groundwater in the Grants by the extensive mining operations in Morrison Formation (Jurassic) Limestone uranium the area and the large-scale dewatering district was also contaminated sandstone uranium deposits deposits Other sandstone uranium Other sedimentary that was required to remove the ore. by other mine-related deposits rocks with uranium activities, including seepage from evaporation ponds and Grants uranium district, San Juan Basin, New Mexico. History Polygons outline approximate areas of uranium mine The Grants district (see map) is a large mill-tailing ponds, mine- subdistricts (from McLemore, 2007). stope leaching, leaching of area within the San Juan Basin, extending accompanying regulations in 1977. These waste materials stored on the surface, and from east of Laguna to west of Gallup. It regulations addressed, among other things, underground-mine disturbance related to comprises eight subdistricts that contained discharges from uranium mines and removal of ore, which introduced oxygen hundreds of mines, including 112 that mills. However, by this time the uranium into the system, causing geochemical produced at least 200,000 pounds of market was already deteriorating and reactions that dissolved contaminants uranium oxide, U3O8. From 1948-1980, the most mines and mills ceased operations into the groundwater. Contaminants Grants district yielded more uranium than shortly thereafter. Therefore, the present in the groundwater system include any other in the United States. More than majority of uranium mining and milling molybdenum, selenium, 226+228radium, 340 million pounds of U3O8 were produced operations in New Mexico predated sulfate, total dissolved solids, and uranium. there from 1948-2002, accounting for 97 environmental laws and regulations. percent of the total production in New Mexico and more than 40 percent of the Regulatory Framework When New Mexico’s regulations were total U.S. production (McLemore, 2002). All conventional underground and promulgated in 1977, a groundwater- open-pit uranium mines in New Mexico protection standard for uranium of Most uranium production in New Mexico closed by 1989, due mainly to economic 5 milligrams per liter (mg/l) was has come from the Morrison Formation, factors. The Federal Clean Water Act established; at that time, neither the World mainly from the Westwater Canyon was passed in 1972 and New Mexico Health Organization (WHO) nor the U.S. Member, a significant aquifer in the followed suit by enacting the New Environmental Protection Agency (EPA) area. Therefore, the formation had to be Mexico Water Quality Act in 1974 and had established a standard. In 1993,

St. Anthony’s Pit, New Mexico. See water quality analysis of pit lake water in table, opposite page.

22 • November/December 2008 • Southwest Hydrology WHO recommended that the limits for deal of assessment work, coordination, and radiological characteristics for uranium One of the few funding that is currently lacking. It also be used until adequate short- and long- will inevitably take a long time, which term studies on the chemical toxicity of encouraging aspects raises the issue of how to protect the public uranium could be completed. Based on is that recovery of from potential health impacts of drinking these limits, the equivalent for natural groundwater levels contaminated water. Very few residents live uranium is approximately 0.14 mg/l. In in the most contaminated portions of the an addendum to the WHO Guidelines, will take upwards of district, but those that do rely on domestic published in 1998, a health-based guideline several hundred years. wells for their primary drinking water value of 0.002 mg/l was established supply. A combination of public education (WHO, 2004). In 2000, EPA issued its and individual water treatment systems may solution would require participation from first uranium drinking water standard of be the only short- and long-term solutions. many different parties, which would likely 0.03 mg/l; this standard is higher than the slow down the process with litigation. WHO standard because it was derived One of the few encouraging aspects is that, based on groundwater modeling, recovery using both health data and economic Obviously, addressing groundwater of groundwater levels will take upwards of considerations. Finally, in 2005 New contamination in the Grants uranium district Mexico revised its uranium standard to is very complicated. It will take a great see Remediation, page 34 0.03 mg/l to be consistent with EPA. Range* of samples collected Surface-water Groundwater Pit lake contaminants Challenges of Groundwater (2004-2005) standard* standard* Remediation molybdenum <0.0055 – 0.020 none 1.0 Addressing groundwater contamination in selenium <0.015 – 0.035 0.05 0.05 the Grants uranium district is complicated uranium 4.2 – 5.3 none 0.03 by several factors: 1) extensive mining and total dissolved solids 23,000 – 32,000 none 1,000 related dewatering activities have created sulfate 16,000 – 25,000 none 600 regional, rather than localized groundwater contamination; 2) underground workings gross alpha 3,050 – 4,590 pCi/l 15 pCi/l none are so extensive that they connect one 226+228radium 11.59 – 24.83 pCi/l 30 pCi/l 30 pCi/l mining operation to another, making it * All measures in mg/l unless otherwise noted. pCi/l = picoCuries per liter difficult to determine responsibilities; Water quality in the St. Anthony’s uranium mine pit lake compared to standards. Comparison for 3) many different companies operated mines compliance is against surface-water standards for the designated use of livestock watering, wildlife habitat, and aquatic life. Concentrations of some contaminants are high, but lacking surface-water throughout the Grants uranium district, standards, are not out of compliance. If pit lake water were to flow into the groundwater system, it and many no longer exist; 4) much of the would have to meet groundwater standards outside the lake. groundwater quality data are dated and large data gaps exist; 5) premining groundwater data are insufficient to establish cleanup criteria; 6) the uranium standard has only recently been established and has been revised over time; and 7) proposed new operations could further cloud the issue of background and cleanup criteria.

Because groundwater is contaminated throughout the district, a regional solution is required. This may take the form of allowing the groundwater system to recover to premining levels to restore geochemical conditions (which could take hundreds to thousands of years), implementing an engineering solution that may involve extraction and treatment to drinking water standards (and possible sale of the resource to offset reclamation costs), or some other solution that lies between these two extremes. Any engineered

November/December 2008 • Southwest Hydrology • 23 Geology, continued from page 21Remediation, continued from page 23 In Situ, continued from page 29 Solution-collapse breccia pipe uranium several hundred years. This isn’t good news Aquifer Impacts? deposits occur in the CPUP, particularly as far as restoring geochemical conditions Before ISR even begins, the uranium in the Grand Canyon region. to premining conditions, but it provides ore-bearing aquifer contains naturally assurance that contaminated groundwater occurring 226radium, 222radon, and other The surface disturbance that results will not migrate and contaminate new areas. uranium-decay products at concentrations from mining this type of deposit exceeding EPA drinking water standards historically has been remarkably small Future Operations (see table below). Nonpotable water because of the high-grade, compact The Grants uranium district still contains such as this can be exempted as an nature of the mineralization and use several hundred million pounds of underground source of drinking water of underground waste rock backfill uranium, now worth $60 per pound of under EPA’s Safe Drinking Water Act, techniques during mine development. A U3O8. This elevated price will only raise and the field of injection and extraction 1,000- to 1,600-foot-deep shaft is usually interest in renewed mining and milling wells can be permitted for Class III required to access the deposits unless in the area. Conventional, open pit, and underground injection control (UIC) the pipe occurs near a deep canyon. stope leach mining have historically been activity. UIC regulations require ISR conducted in the Grants uranium district; operations to be designed to produce Breccia pipe ore grades are at least as all these methods, along with in-situ only from the exempted area, and high as any other global uranium-deposit leaching, may be proposed in the future. monitoring must demonstrate that type, at 0.4 to 1 percent, because the the leach solution is contained within limited size of the pipe concentrates the Environmental regulations that were the ore zone. Monitoring parameters uranium. Average ore reserves for an absent during most of the past mining are typically chosen that are high in individual mineralized pipe are about 3.5 activities are now in place, along with concentration compared to surrounding million pounds U 0 , with an average 3 8 more stringent mining regulations ambient groundwater, are robust, and may grade of about 0.6 percent uranium. that will protect human health and the be rapidly analyzed at site laboratories. environment to a much greater degree. If Parameters such as conductivity, Volcanic uranium deposits are found water produced during new dewatering in volcanic and volcaniclastic rocks. chloride, bicarbonate, sulfate, and activities will be discharged to the surface, uranium are common. Restoration must Volcanic deposits and hydrothermal it will have to be treated to groundwater veins occur in rhyolitic flows and be completed before monitoring ceases, and possibly drinking-water standards to prevent regional contamination. tuffaceous ash flows, formed by prior to discharge. This will help prevent hydrothermal, hot springs, or meteoric additional contamination, but water Construction, operation, monitoring, and waters. Tabular lacustrine sandstone discharged to the surface could remobilize reporting at ISR sites in the United States deposits occur in carbonaceous any contamination still present in the soil have been highly successful in ensuring tuffaceous sandstone and mudstones, from the previous operational period if not that leach solution remains confined to deposited by cooler groundwaters. addressed before new operations begin. the exempted ore zone, as required by This and continued exposure and oxidation Several major uranium deposits in the UIC regulations. As a result of these of the ore body above the water table will RMIBUP occur as veins in metamorphic practices and the fact that the ore bodies continue to present challenges in managing and sedimentary rocks, primarily are not in drinking-water-quality aquifers, potential contamination. However, the within the Front Range and central ISR uranium operations have caused no current regulations include flexibility to Rocky Mountains of Colorado. Here, adverse impact to underground sources require protective engineering controls hydrothermal fluids directly deposited of drinking water in the United States. during operations and adequate financial the uranium in fracture systems. Most assurance to address closure requirements. Contact Mark Pelizza at of the BRUP deposits are volcanic, [email protected]. occurring as vein deposits and tabular Contact Jerry Schoeppner at ore bodies in paleolake sediments [email protected]. Parameter Average EPA MCL associated with volcanic activity. uranium (ppb) 488 30 Volcanic deposits generally are developed References 226 by conventional mining methods. McLemore, V.T., 2002. Database of Uranium Mines, radium (pCi/l) 215 5.0 Prospects, Occurrences, and Mills in New 222radon (pCi/l) 207,133 300 Contact Clyde Yancey at [email protected]. Mexico, New Mexico Bur. Geology and Mineral Resources, Open-file Report 461, 11 pp. gross alpha (pCi/l) 865 15 McLemore, V.T., 2007. Uranium resources in New Mexico, Society for Mining, Metallurgy, and Water quality data from 89 baseline wells, Reference Exploration 2007 Annual Meeting, SME collected prior to initiation of ISR operations, in Finch, W.I., 1996. Uranium Provinces of North preprint 07-111. the mineralized portion of the Oakville aquifer America, Their Definition, Distribution, and World Health Organization, 2004. Guidelines for at the URI Inc. Vasquez ISR project in Duval Models, U.S. Geological Survey Bulletin 2141, County, Texas. EPA’s maximum contaminant U.S. Department of the Interior. Drinking-water Quality: Summary Statement, 3rd ed., Geneva, WHO. levels (MCLs) are shown for comparison.

34 • November/December 2008 • Southwest Hydrology