Groundwater Flow Model Construction and Calibration

Document ID: 013230
2010

Rosemont Copper Company (Rosemont) is planning the development of an open pit mining and mineral processing operation known as the Rosemont Copper Project (Project) on the east side of the Santa Rita Mountains, approximately 30 miles southeast of Tucson Arizona in Pima, County (Figure 1). As part of the mining operation, dewatering of the Open Pit will continue throughout the 20-25 years of operation and cease at closure. When mining ceases and dewatering is discontinued, the pit will naturally refill with water from groundwater, surface- water, and precipitation contributions and a pit lake will form. It is expected that the pit will remain a perpetual hydraulic sink at a stabilized, equilibrium condition due to the high evaporation rate of the Rosemont area. This implies that groundwater will perpetually flow into the Open Pit, although at a much lower rate than during the active dewatering process.

Tetra Tech has constructed regional groundwater flow models for the Project. These flow models represent pre-mining steady state conditi ons, active mining conditions, and post-closure mining conditions. In support of the groundwater flow model development, the following supporting tasks were performed such as development of a Davidson Canyon conceptual model, hydrogeologic framework model, recharge di stribution, steady-state water levels and potentiometric surface, evaluation of aquifer testing and hydraulic properties, evapotranspiration distribution, and stream-flow conditions.

This Technical Memorandum documents the tasks completed to construct 1) the steady-state groundwater flow model and calibration results, 2) the mining-phase groundwater flow model, and 3) the post-mining phase groundwater flow model. The background information provided in this Technical Memorandum supports the groun dwater impact analysis and sensitivity analysis tasks being developed by Tetra Tech. These analyses will be presented in subsequent technical memoranda.

O'Brien, G. 2010a. Technical Memorandum: Groundwater Flow Model Construction and Calibration. Document No. 198/10-320874-5.3. Prepared for Rosemont Copper Company. Tucson, Arizona: Tetra Tech. July 26.