Smoky Canyon Phosphate Mine (Idaho)
The Smoky Canyon Mine is an operating phosphate mine and mill operation in southeastern Idaho. Phosphate mining began in 1983 and will continue for the next 10 to 20 years. The primary environmental concern at this site is the potential for mobilization and transport of selenium from overburden waste rock to groundwater and surface water downgradient of the mine. Environmental conditions in the historical mining areas are being evaluated and addressed by the mine operator, with regulatory oversight by the U.S. Forest Service, in accordance with the Superfund/CERCLA process for remedy development and implementation.
Remedial Investigation (RI)
Formation worked on behalf of the mine operator to design, plan, and implement a multi-media environmental investigation. Numerous environmental data sets were available from previous site characterization investigations and the mine’s long-term environmental monitoring programs, and these existing data were utilized to the extent possible to characterize the site conditions and develop a focused scope of work for the RI. Additional environmental data were collected to characterize terrestrial and aquatic ecosystems, including chemical data for biotic and abiotic media. Formation is now conducting the baseline human-health and ecological risk assessments using these additional data.
Hydrogeology and Groundwater
Formation Environmental personnel have been providing technical support and analyses for evaluating and addressing groundwater quality issues associated with historical and active mining operations across the site. Formation has utilized a wide range of field and analytical tools to understand a complex history of mining, selenium mobilization and transport, and related effects on groundwater quality over time. Related field studies completed by Formation include:
- Monitoring well design and installation to access groundwater at depths of over 1,100 feet
- Geophysical and hydrophysical logging and discrete-depth sampling
- Surface geophysical survey for groundwater flow characterization
- Aquifer testing
- Long-term, continuous water-level monitoring at multiple deep-aquifer locations
- Routine surface water and groundwater quality monitoring and reporting
- Permitting, design, and installation for a water-supply well.
Formation Environmental is performing modeling analyses to characterize the fate and transport of chemical constituents in groundwater. Formation facilitated a collaborative, model-development process, which included our client and Federal and State regulatory agencies and their consultants. The collaborative process provided a forum for technical discussions of the modeling objectives and approach. The process benefited the project by progressively building a common understanding and agreement.
Our modeling team integrated more than 25 years of mining, overburden disposal, reclamation, and removal actions to account for the observed changes in site conditions over time, including selenium transport to groundwater and surface water. The infiltration models HELP3 and VADOSE/W were used to estimate infiltration rates through overburden cover materials and designs that have been used to cover overburden waste rock over the history of mine operations. GIS served as an automated interface with a groundwater-flow and contaminant-transport model.
The model supports ongoing site characterization efforts and also works as a valuable tool for evaluating remedial alternatives and reclamation strategies addressed in the Feasibility Study.
Formation Environmental designed pilot-scale treatability studies of four distinct technologies that remove selenium from water.
- Zero-valent iron
- Semi-passive bioreactor
- Microbial selenium reduction
- Biological selenium reduction coupled with reverse-osmosis
Formation evaluated numerous treatment technologies for potential implementation issues under challenging site conditions (e.g., limited access to remote locations, high altitude, and extreme cold throughout the winter season). Three passive treatment technologies and one active treatment method were ultimately selected for on-site field testing. Formation prepared the treatability study design documents, in consultation with technology vendors, and coordinated implementation, data collection, and reporting associated with each study.
These studies provide the “real-world” data needed to perform reliable comparative analyses of the implementability, effectiveness, and costs of remedial alternatives that include water-treatment components.
Formation Environmental personnel designed two removal actions selected to reduce the transport of chemicals of concern, including selenium, from the Pole Canyon overburden disposal area at the Smoky Canyon Mine.
The first removal action re-routed Pole Canyon Creek around 26 million cubic yards of overburden waste rock disposed in Pole Canyon. The upstream creek flow was directed into a 10,000-foot long, 30-inch diameter pipeline and then routed back to the original creek channel below the overburden area. Re-routing the creek eliminated the primary source of water to the overburden. Other components of the removal action included an infiltration basin constructed upstream of overburden materials to capture and direct clean run-on water to the bedrock aquifer and a run-on control channel designed to divert estimated flow from a 100-year, 24-hour storm event away from Pole Canyon. These components were included to further reduce water entry into and contact with overburden materials in the canyon.
The second removal action is currently being designed by Formation and will involve construction of a composite cover on 120 acres of overburden in Pole Canyon.
The cover will consist of approximately 2 feet of granular chert material overlain by approximately 3 feet of growth medium (Dinwoody Formation shale) to support new vegetation. The composite cover is designed to reduce infiltration into overburden from incident precipitation and further limit mobilization and transport of selenium to the environment.