Our Section completed remediation at the Skyline Mine in Fall of 2011. Skyline is located in Monument Valley Utah and is one of 520 abandoned uranium mines located on the Navajo Reservation, an area the size of West Virginia. From 1944 to 1986, nearly four million tons of uranium ore were extracted from Navajo lands to support Cold War uranium development. Today the mines are closed, but a legacy of abandoned uranium mines remains. Chronic exposure to uranium mine waste, and especially associated radium contamination, poses a risk of lung cancer, bone cancer, and impaired kidney function. In 2008, EPA and 4 other federal agencies put in place the first comprehensive plan to address this problem.
Our OSC, Jason Musante, spent weeks on the reservation, meeting with residents and community leaders, and spending evenings and weekends attending local government meetings in order to develop ideas for the Skyline Mine cleanup. An agreement was reached to dispose the wastes on top of the 800 foot tall Oljato Mesa. The local community passed a resolution in support of the plan, and the Navajo EPA concurred. During its operation, the Skyline Mine used a complex cable and gondola system to move uranium ore from the mesa-top mine to the floor of Monument Valley. The operation resulted in thousands of tons of radium-contaminated soil left on top of the cliff, scattered along a steep slope at the cliff edge, and covering the base of the 800 foot cliff. The mesa top was nearly inaccessible, with nothing but a washed out trail running up the back side. Moving this volume of waste from the valley floor to the mesa top by truck was not possible; the narrow road was barely passable. Instead, we moved 35,000 tons of contaminated soil up the face of the cliff by constructing a reverse version of the gondola system used 40 years prior by the mining company to move the waste from the top of the mesa to the bottom.
EPA excavated these contaminated soils removing radium-226 contamination as high as 200 picoCuries per gram and 1 million counts per minute gamma radiation. We used state of the art risk modeling to establish health-risk based thresholds for radium contamination and conducted significant investigation including background characterization tailored to the Site and its environs. Using advanced monitoring and sampling techniques we were able to achieve concentration reduction from over 200 pCi/g Radium to less than 5 pCi/g, achieving a cancer risk reduction of more than 40 times for those nearest neighbors to some of the contaminated areas.
Set in the scenic Monument Valley of southern Utah, an engineering marvel of this magnitude was spellbinding to residents and the press, and we spent hours providing information and tours to people that thought the mine might never be cleaned up. Our experiences in this regard have since been shared with others across the EPA Regions as a model of how to engage community members in complex, collaborative problem-solving to reach environmentally protective and politically satisfactory conclusions.
In order to get rock and other waste cover materials for use in containing contaminants at remote mountain sites, such as the Klondyke Tailings Site, it may be advisable to create your own quarry using a screen plant. The screen plant is portable contains multiple screens of varying sizes. In the case of Kondyke, it was desirable to screen out 8″ plus size material first, then sort 8″ – 4″, 4″ – 2″ and 2″ minus for various uses at the Site. The screen plant will do an expert job “sorting” those materials for use to various ends. Recently at Klondyke, we set one up in order to generate needed materials on site, saving money in transportation and significantly decreasing the carbon footprint of the work.
In order to fill our gabion baskets, create a suitable waste cover to limit percolation, and to reduce erosive loss of said cover due to wind and rain, different size materials, and sometimes blends are required. For example, gabion basket specifications from the manufacturer call for 8″ – 4″ diameter rock – in rows 2 deep within each basket. These materials were spit out of the screen plant in the first tier and collected via large articulated dumps and staged. Meanwhile, 2″-4″ material was churned out providing useful spoils for waste cover “top dressing” aimed at reducing erosive loss due to wind and rain. Finally, 2″ minus materials, the greatest in quantity, were collected and similarly staged. Two-inch minus makes an excellent backfill material and can, with conditioning, help achieve desirable cover parameters such as thickness, due to the large volume, and water holding capacity if blended properly.
The screen plant was established in a ephemeral river valley or “arroyo” where the main watercourse is a dry wash most of the year. Summer monsoons create very high flows, sometimes leaving still waters with suspended fine grained materials stranded above the creek’s bankfull stage. Based on the stream dynamics, i.e., high flow/high sediment load mid-summer gully-washers, it is not anticipated that the “quarry site” will last or have any long-term effect on the channel morphology. Further, just beyond the 100-year flood plain, we discovered a silty clay source some 3′ thick and approximately 1 acre in size. This material can also be mined to blend with the 2″ minus to improve conditioning. Better conditioning will increase compact ability to achieve conductivity goals but also it provide needed organic matter content for revegetation in the cover blend. This blend, coupled with a 4″ – 2″ top dress should do a great job slowing erosive forces while making suitable soil for local plants to flourish – a great antidote to erosive loss in and of itself.
Basically the cleanup plan entails rounding up tailings material that has escaped and corralling it in a second waste repository. An earlier repository was completed in 2007. Remaining tailings wastes, and contaminated soils scattered on adjacent residential lands, will be removed and deposited at the new repository.
Repository “gabion”(or basket) rock walls will be installed like so:
Gabion walls are designed to be high enough to sustain 100-year flooding conditions and substantial enough to withstand expected water flow velocities during those worst case flood conditions.
Additionally, the soil cap on the repository must resist erosion but since only a small amount of water shed is expected, i.e., only the area of the cap itself heavy erosion due to storm water runoff is not expected. Rather, wind erosion may be the primary erosive loss concern on the cap itself. To resist both water and wind erosion techniques must be used to ensure the proper grade, material mix and other armoring. The armoring, or rip-rap rock in most cases, should be substantial enough to resist the wind and water velocities associated with storm events. Both wind or rain storms would generate high velocity erosion, testing the mettle of the cap. Also, the material itself should be compacted and of appropriate particle size to resist erosion.
A final word on this idea. Our engineers have modeled a particle size mix that should in fact be largely resistant to erosive forces and also be amenable to plant growth which will further mitigate erosion threats. The idea here is to create a “water balance cover” where potential plant transpiration (PET) is in a nearly 1:1 ratio with precipitation (P). Significant plant growth will, with time, remove most of the water from the cap, preventing percolation of course, but also potential liquefaction and concomitant mass wasting.
The Klondyke Tailings Site is located in the unincorporated town of Klondye, Graham County, AZ (about 3 hours southeast of Phoenix). It is situated slightly upstream of the Aravaipa wilderness area along the Aravaipa Creek. The Site processed copper ore from the 1940s through the 60s. US EPA and the AZ Department of Environmental Quality will begin cleanup of the Site in May 2012.
The plan includes consolidation of tailings and contaminated soils from the bottom of the Aravaipa wash and it’s “shorelines” including an uncontrolled pile and contaminated soils on residential properties. We plan to grab this material and push it into a pile that can be contained using a gabion basket system and a cap system. The basket system and as-built height was designed to withstand a 100-year storm event. Basket wall height and rock size distribution were modeled using hydrologic data. The cap was designed for thickness first to reduce percolation rates into the contaminated material. After further study however, the team determined that the primary objective was to discourage wind erosion that would lead to cap compromise.
Environmental cleanup is my passion. Growing up amidst the pollution recognition movement, and with a Father who was active in domestic and international cleanups of contaminated sites, I developed this passion and had the opportunity to take my awareness and experience and use it as a building block for an exciting career in environmental remediation. As an On-Scene Coordinator at USEPA since 2002, I’ve had the chance to clean up numerous sites and oversee cleanups at many more. These sites have ranged from urban industrial sites like metal plating sites, to rural sites like pesticide crop duster sites and abandoned mine sites. I have had the chance to implement numerous alternative treatment technologies.
The purpose of this site is to share and gather perspectives on environmental cleanup, response, remediation and restoration of contaminated sites. I hope you’ll read and share this blog going forward. Hope you enjoy it!