Mining

Client: Compañía Pangea Minera /McEwen Mining
Location: Mina El Gallo, Sierra Madre Occidental, Sinaloa, Mexico

Challenge: To store tailings produced by reprocessing gold leaching piles in a cost-effective manner that is protective of the environment. 

Solution: We determined that the safest and most economical solution for storing the tailings was to place them in one of the inactive mine pits. To accomplish this, INTERA characterized the hydrogeology of the pit and the geochemistry of the tailings and potentially reactive surfaces of the pit. These efforts supported the preparation and submittal of a successful permit application to the SEMARNAT for the in-pit disposal of tailings from reprocessed ore . A hydraulic testing program was conducted to characterize the andesite aquifer adjacent to the candidate pit. The program consisted of drilling five deep core holes (approximately 200 meters each) to identify fractures that could conduct groundwater, performing packer tests, and installing vibrating wire piezometers. To achieve a better understanding of groundwater flow, we also collected hydraulic field data, performed a water balance for the pit, and oversaw the development of a hydrogeological conceptual model of regional and local groundwater flow systems. The geochemistry program included static geochemical analyses of tailings and pit surfaces, and a hydrochemical assessment of seeps in the pit. 

Results: Our hydrogeological and geochemical evaluations showed that most of the groundwater flow is through fractures under the pit, the tailings have no potential for acid generation, and that the contrast between the hydrogeological characteristics of the tailings and the fractured rock will minimize the inflow of groundwater and the outflow of tailings solutions during their consolidation. The permit for in-pit tailings storage obtained from the SERMANAT was the first of its kind issued in Mexico. 

Client: Rio Algom Mining LLC
Location: McKinley County, New Mexico, USA

Challenge. Perform characterization and analyses needed to obtain regulatory approval of alternate concentration limits (ACLs) and alternative abatement standards (AASs) for closure of a uranium mill site

Solution. The Rio Algom Mine and Mill Site is located in the Ambrosia Lake Valley Sub-district of the Grants Uranium Mining District. Approximately 22 miles long, it is estimated that this mining district consists of hundreds of interconnected shafts and vents. INTERA staff conducted a hydrogeologic assessment of Rio Algom’s mine sites in the Ambrosia Lake area that included an evaluation of: an alluvial aquifer created as a result of mine dewatering activities, the manner in which alluvial waters may be connected to deeper aquifers, the water quality of deeper aquifers, and the nature and extent of constituents in excess of New Mexico Water Quality Control Commission standards. As a result of the hydrogeologic assessment and to support closure of the Quivera Mill, INTERA staff prepared an ACL application to the United States Nuclear Regulatory Commission (USNRC) for molybdenum, nickel, selenium, gross alpha, radium-226+228, thorium-230, natural uranium, and lead-210. The purpose of the ACL application was to replace the licensed maximum contaminant levels in groundwater with alternate levels that are still protective of human health and the environment while also being as low as reasonably achievable (ALARA). The ACL addressed source and contaminant characterization, contaminant transport, exposure assessment (both human health and ecological), assessment of the corrective action efforts, and an ALARA demonstration. Both groundwater and geochemical modeling were used in this effort. The ACL application was subsequently approved by the USNRC, thereby allowing discontinuation of the corrective action plan for groundwater. Additional activities include compiling regional hydrogeologic data, developing a conceptual hydrogeologic model, and developing and applying a 3-dimensional groundwater flow model. Results of our analyses have confirmed that a regional cone of depression that developed during the period of mine dewatering is still present in the area and will likely take hundreds of years to recover. Groundwater flow directions in response to this cone of depression are towards the center of the valley and away from existing receptors. Since some constituents of concern in groundwater naturally exceed standards, particularly in the alluvial and ore-bearing aquifers, natural attenuation mechanisms are active, and negative impacts to water resources being used in the area are unlikely, the closure strategy includes receiving approval for AASs from the New Mexico Water Quality Control Commission to close the site with the State of New Mexico.

Client: Uranium Energy Corporation
Location: Karnes County, Texas, USA

Challenge. Evaluate and incorporate geologic and hydrogeologic information as part of the application to obtain a radioactive material license for the refurbishment and re-start of an in-situ recovery (ISR) uranium processing facility that sat idle for more than a decade

Solution. INTERA compiled and organized data on site physiography, climate, geology, hydrostratigraphy, subsurface hydraulic properties, structure, water levels, regional groundwater flow, recharge, discharge, and water quality, as well as interaction of the groundwater system with streams, lakes, and springs. A significant portion of our efforts focused on conducting a detailed assessment of the Gulf Coast, Carrizo-Wilcox, and Yegua-Jackson aquifers in south-central Texas near the project area. All of this information was integrated with the other license application components to assess the potential environmental impacts of operating the facility. After receiving the license, the Hobson Facility was completely refurbished and is a fully operational processing plant for uranium resins and yellowcake.

Client: General Electric/United Nuclear Corporation (UNC)
Location: Cibola County, New Mexico, USA

Challenge. Develop and implement remedial action strategy and plan for closing an inactive uranium mine site

Solution. INTERA has developed technical and regulatory strategies for site characterization and closure of this inactive uranium mine site that includes a pit lake, a dry pit area, non-economic ore piles, and overburden piles associated with past mining activities. The site is being closed under the New Mexico Environment Department’s (NMED) abatement regulations. Our tasks have included surface water and groundwater impact investigations and modeling; aquifer testing; recharge analysis; pit lake characterization; development of an overburden characterization approach; and a remedial alternative feasibility analysis. The overburden characterization approach was patterned after a compositing methodology developed by the United States Geological Survey that focuses on the potential for erosion processes to cause impacts to surface water and groundwater. INTERA demonstrated the effects of a distributed ore zone on the variability in groundwater quality at the site and how natural attenuation is preventing the spread of contamination. We used a multiple accounts analysis process to evaluate remedial alternatives for tracking numerous inputs from multiple stakeholders and developed a GIS-based tool to allow users from various locations to perform alternatives analysis. INTERA has led the stakeholder involvement process which has resulted in agreement and acceptance of the final remedial action strategies. We also developed an innovative approach for development of an alternative abatement standard (AAS) petition that relies on integration of detailed vadose zone, groundwater, and geochemical sampling, instrumentation and modeling to demonstrate no migration. The Stage 2 Abatement Plan, which includes the AASs that are being proposed to the Water Quality Control Commission was approved by the NMED. Implementing this abatement strategy will result in a more cost-effective remedial action at the site that is still protective of human health and the environment.