Hydrogeologic Framework Model

Document ID: 012943

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. 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.

Rosemont has contracted Tetra Tech to develop regional groundwater flow models for the Project. These flow models will represent pre-mining steady state conditions, active mining conditions, and post-closure mining conditions. Tetra Tech has undertaken several tasks to support development of these groundwater flow models. These tasks include development of a Davidson Canyon conceptual model, hydrogeologic framework model, recharge distribution, steady-state water levels and potentiometric surface, evaluation of aquifer testing and hydraulic properties, evapotranspiration distribution, and st reamflow conditions. Upon completion of the groundwater flow models, Tetra Tech will document the model construction process, calibration results, flow model predictions, and sensitivity analyses.

This technical memorandum documents the tasks completed to develop a 3-dimensional hydrogeologic framework model from the 2-dimens ional horizontal hydrogeologic data provided by Montgomery & Associates (M&A). This 3-di mensional hydrogeologic framework model will be incorporated into the regional groundwater flow models being developed by Tetra Tech.

O'Brien, G. 2010b. Technical Memorandum: Hydrogeologic Framework Model. Document No. 170/10-320874-5.3. Prepared for Rosemont Copper Company. Tucson, Arizona: Tetra Tech. July 9.