EIS & Water Supply Support for the Rosemont Project

M&A hydrogeologists, groundwater modelers, and water policy experts worked closely with a team of engineers, geochemists, and regulatory and legal experts on this project. The final Record of Decision from the U.S. Forest Service is pending.

Overview

The Rosemont Project is a proposed open-pit mining operation (copper, molybdenum, and silver) in the northern part of the Santa Rita Mountains, about 30 miles southeast of Tucson in the Cienega Creek basin. The mine setting is geologically complex, with groundwater movement controlled largely by fracture heterogeneities and fault features. The bulk of the water supply for the mine will be obtained from a wellfield located in the Santa Cruz Valley basin-fill aquifer, 12 to 14 miles away. Plans call for a state-of-the-art operation with respect to water conservation and recycling, environmental controls, land reclamation, and air emissions.

Services

M&A’s services ranged from initial site investigations to the development of multiple groundwater flow models in the mine and wellfield areas for this proposed mine.

Environmental Impact Studies

  • Analyzed geologic, hydrologic, and environmental information for the mine and surrounding region
  • Installed 36 characterization and monitoring wells and conducted extensive aquifer testing
  • Prepared the hydrogeology portions of the EIS report and presented findings to regulatory review committees
  • Designed and implemented a program for monitoring water levels in wells and springs
  • Developed a database of several hundred residential wells in the vicinity of the proposed mine and wellfield areas and designed a long-term monitoring program for these wells

Water Policy & Planning

  • Evaluated all options for mine water supply and identified the most reliable, institutionally viable, and environmentally sound alternative
  • Managed the water supply team, which includes hydrogeologists, water resource planners, engineers, and attorneys
  • Investigated the feasibility of using artificial recharge to replace water withdrawn for mining supplies
  • Developed and implemented a strategy for replenishing 105 percent of the mine’s projected use by purchasing CAP water for recharge within the Tucson AMA
  • Addressed regulatory and legal issues related to water rights, permitting, well development, and recharge

Mine Dewatering / Groundwater Modeling

  • Developed a groundwater flow model to predict pit dewatering requirements and post-mining pit-lake development
  • Projected groundwater-related impacts associated with mining operations
  • Updated the model in response to draft EIS comments
  • Conducted initial investigations of pit dewatering and depressurization to support the geotechnical design
  • Developed a second groundwater flow model to evaluate impacts associated with the proposed production wellfield in the Santa Cruz basin