Surface Water and Riparian Studies Summary

Surface Water & Riparian

Surface Water & Riparian

TITLE: Baseline Regulatory (100-Year) Hydrology and Average-Annual Runoff RELEASE DATE: March 2010 PREPARED BY: Tetra Tech Brief Summary: Under baseline conditions, stormwater runoff from the Rosemont drainage area flows down four main pathways – McCleary Canyon, Wasp Canyon, and Barrel Canyon and Lower Barrel Canyon – to the general outlet point (Compliance Point) for the watershed to the northeast of the project site. In this report, Tetra Tech provides details on the flow generated in those drainages.

Both the peak flow from the 100-year storm event and average runoff conditions at the Rosemont site were calculated. Tetra Tech’s baseline average-annual runoff analysis for watersheds within the project site indicate annual precipitation of approximately 18 inches with the following average annual runoff (provided in acre-feet): McCleary Canyon-322, Wasp Canyon-310, Barrel Canyon-354, Lower Barrel Canyon-142, and Compliance Point-912.

Surface water and riparian studies looked at vegetative cover and riparian mapping to establish baselines and compare potential impacts from Rosemont project operations.

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TITLE: Davidson Canyon Hydrogeologic Conceptual Model and Assessment of Spring Impacts RELEASE DATE: April 2010 PREPARED BY: Tetra Tech Brief Summary: The Rosemont project site comprises approximately 16 percent of the entire Davidson Canyon watershed; therefore, the project has the potential to impact water resources in that drainage, according to this Tetra Tech report. However, the anticipated downstream effects of pit dewatering and the post-mining pit lake may be indiscernible from the existing natural and man-induced regional conditions.

During operations, dewatering (taking water out of the pit) will create drawdown in the groundwater table in an area immediately surrounding the pit. The water will follow the path of least resistance or in this case, the most permeable or most fractured rocks. The drawdown will be greatest around the pit and will diminish farther away from the pit, such as in Davidson Canyon, a

distance of nine to 14 miles.

Stormwater flow will likely be reduced downstream.

However, flow-through drains and diversion channels will be constructed to help pass stormwater downstream of the facilities. Most of the stormwater entering the drains will likely infiltrate and ultimately recharge, as opposed to passing through as downstream surface flows. Flow modeling suggests that groundwater levels could eventually be one to 10 feet lower in parts of Davidson Canyon, but natural fluctuations in groundwater levels in that complex system already range from four to 25 feet, thus any declines are likely to be indiscernible from current conditions.

Impacts on water resources in Davidson Canyon and the larger Cienega Creek basin should be considered in the context of long-term pit inflows. It is estimated that inflows will be more than 300 gallons per minute (gpm) at the end of mining and decrease to about 120 gpm after 100 years.

Current water users are tapping the regional groundwater system in the Davidson Canyon watershed to supply water to homes, ranches and small businesses. The state groundwater well registry database (ADWR) indicates that there are more than 300 wells (monitoring wells excluded) within the Davidson Canyon watershed. The actual pumping rates for these wells are not reported.

Most springs appear to be fed by shallow water sources that are strongly influenced by seasonal precipitation variations and not connected to groundwater systems.

TITLE: Davidson Canyon Hydrogeologic Conceptual Model and Assessment of Spring Impacts (Updated Report) RELEASE DATE: July 2010 PREPARED BY: Tetra Tech Brief Summary: The Rosemont project site comprises approximately 16 percent of the entire Davidson Canyon watershed, therefore the project has the potential to impact water resources in that drainage. The anticipated downstream effects of pit dewatering and the post-mining pit lake may be indiscernible from the existing natural and man-induced regional conditions.

At-a-glance: • The Tetra Tech report provides detailed data on surface water hydrology, channel morphology, geology, geologic controls on streamflow, groundwater hydrology and the regional bedrock flow system. The discussion of groundwater-surface water interactions documents possible impacts on the Davidson Canyon watershed, with particular attention to the areas like

Lower Davidson that are farthest from the proposed Rosemont project.

• Impacts on riparian trees and other vegetation are likely to be minimal considering their distance from the project site and the long periods over which the potential impacts would materialize (hundreds of years). It is possible that those impacts will fall within the range of natural fluctuations and thus will be within the range of tolerated conditions.

• The Rosemont Waste Rock Storage Area, Heap Leach Facility, and the Dry Stack Tailings Facility will have little or no impact on the quality of water within the regional groundwater system.

TITLE: Dry Stack Tailings Storage Facility Stormwater Management Design Report RELEASE DATE: April 2009; updated in 2010 PREPARED BY: AMEC Earth & Environmental, Inc. Brief Summary: AMEC Earth & Environment, Inc. describes the stormwater management design process for the Dry Stack Tailings Storage Facility (TSF) in McCleary Canyon and in the Lower Barrel Canyon drainage areas east of the plant site. The first phase of the TSF will have a capacity of 343 million tons and will operate for 12 years. The second phase will extend into McCleary Canyon with a capacity of 253 million tons and will operate for slightly less than nine years.

In addition, AMEC defined stormwater parameters, operations requirements, reclamation suggestions, and outlined a closure/post-closure plan aimed at eliminating any reasonable probability of discharge.

No impact on aquifer water quality is anticipated during the operational, closure, and post-closure periods of the facility. Therefore, the focus of the closure/post-closure strategy is to minimize erosion and promote landform stability.

TITLE: Flow Through Drain (Sizing) RELEASE DATE: April 2010 PREPARED BY: Tetra Tech TITLE: Flow Through Drain Design RELEASE DATE: April 2010 PREPARED BY: Tetra Tech TITLE: Flow Through Drain Design Summary RELEASE DATE: August 2010 PREPARED BY: Tetra Tech

TITLE: Hydrology Method Justification RELEASE DATE: January 2010 PREPARED BY: Tetra Tech TITLE: Infiltration Analysis RELEASE DATE: April 2010 PREPARED BY: Tetra Tech TITLE: Onsite Riparian Habitat Assessment and Impact Analysis RELEASE DATE: April 2010 PREPARED BY: WestLand Resources, Inc. Brief Summary: WestLand Resources was asked to describe and map riparian habitat within portions of the Rosemont claim holdings located in the Santa Rita Mountains. The study area consists of approximately 10,493 acres and encompassed all of the project alternatives being considered by the Forest Service for the site at the time of the study. Of this total, riparian habitat makes up 316.7 acres, or three percent of the study area. This work supports the development and comparison of alternatives that seek to reduce the impacts of the project on riparian habitat.

The study area contains two vegetative cover types – Madrean evergreen woodlands in the high elevations, and semi-desert grassland in the lower elevations. Historical information suggests that the vegetation communities within the area have changed significantly since the arrival of Euro-Americans and the introduction of mining and grazing, including an increase in woody species and a reduced density of grasses.

In addition to riparian mapping and vegetative cover analysis, Westland Resources inspected Rosemont holdings for waters of the area including wetlands, springs, seeps and other water resources such as stock tanks.

TITLE: Pit Diversion Channel Design RELEASE DATE: April 2010 PREPARED BY: Tetra Tech Brief Summary: The Rosemont pit diversion channel and related structures are designed to carry stormwater runoff caused by a probable maximum precipitation (PMP) storm event. At peak flow, the channel will safely divert the water from west and south of the pit at peak flow into the upper portion of Barrel Canyon.

The channel will be a permanent structure located to the west of the open pit, and will be constructed early in the life of the Rosemont project. Over time, the rosemont copper

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Waste Rock Storage Area will confine the flows within perimeter containment basins. These basins are located between the toe of the Waste Rock Storage Area and a natural ridgeline.

The Tetra Tech report estimates precipitation during the PMP storm event and provides details on hydrologic soil groups and their infiltration rates in a storm and the flow rates through the channel at various points.

TITLE: Post-Mining Regulatory (100-Year) Hydrology and Average Annual Runoff RELEASE DATE: March 2010 PREPARED BY: Tetra Tech TITLE: Rainfall Run Off Volumes – Rosemont Heap Leach Facility RELEASE DATE: April 2009 PREPARED BY: Tetra Tech TITLE: Design Storm and Precipitation Data/Design Criteria RELEASE DATE: April 2009 PREPARED BY: Tetra Tech TITLE: Modified Infiltration Rate RELEASE DATE: May 2009 PREPARED BY: Tetra Tech TITLE: Sediment Delivery RELEASE DATE: April 2010 PREPARED BY: Tetra Tech TITLE: Baseline and Post-Mining Conditions – Sediment Delivery Alternatives RELEASE DATE: April 2010 PREPARED BY: Tetra Tech TITLE: Site Water Management Update Volumes 1 - 5 RELEASE DATE: April 2010 PREPARED BY: Tetra Tech TITLE: Site Soil Erosion Estimates RELEASE DATE: March 2010 PREPARED BY: Tetra Tech TITLE: Surface Water Quality Baseline Analysis RELEASE DATE: April 2010 PREPARED BY: Tetra Tech 36

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TITLE: Waste Rock Storage Area Stormwater Management RELEASE DATE: April 2010 PREPARED BY: Tetra Tech