DESCRIPCIÓN DE LAS PRINCIPALES CUENTAS COMPONENTES

Water management within the project area is divided into process and non-process water. Process water is water that will be used in the plant or will be conveyed around the site via pipelines. On an annual basis, the process water circuit will be in a surplus condition and to avoid continuous and on- going accruals of water the excess amounts will be released at a controlled rate each year during the wet season. Releases will be from the TMF into the Chilloroya River and will only occur upon the

achievement of adequate quality. The wet season discharges will take place when the Chilloroya River has a large assimilative flow. The water will be treated if necessary before release.

Non-process water is surface drainage and runoff water that will require management at the site. It will be comprised of two streams: contact and non-contact water. Contact water is water that will come into contact with facilities such as the pit, stockpiles, the plant site, PAG WRF, etc. This water will be collected in designated ponds for treatment, if necessary, prior to its release. To the maximum extent possible this water will be used in the process. Non-contact water will be directed around the facilities via diversion channels and discharged into natural drainages upon the achievement of sediment removal to acceptable levels.

Hydrology and hydraulic analyses, including a detailed process water balance, have been completed to determine the types, locations and sizes of the water management structures as well as the times and quantities of discharges. The following sections discuss water management for the project.

1.9.1 Process water

Water for the mill will be supplied from the following sources: groundwater from dewatering wells located behind the pit walls, in pit surface water collected in the pit sumps, drainage from the PAG WRF that will be collected in the containment pond just below the PAG WRF, and reclaimed water from the surface water pond in the TMF. A temporary water reservoir will be available within the TMF in 2011, to collect and impound water to support the start of operations in early 2013.

Raw water for sustaining mill operations will be obtained, in part, from pit dewatering wells installed behind the pit perimeter. Based on the current hydrogeologic model, a total of 18 dewatering wells will be installed in and around the pit. Water from these wells will be pumped to a collection box immediately upstream of the plant and then conveyed by gravity to a dedicated tank in the plant. Water from the PAG WRF and in-pit sumps is expected to be acidic and will be neutralised with lime at the process plant before use in the process.

When the total volume of water available to the mill from the pit, TMF and PAG WRF exceeds the volume required, the excess amount will be removed from the pit groundwater component and a gravity flow pipeline will convey this from the pit dewatering wells system to the environment upon confirmation of adequate water quality. The priority will be to recycle as much water as possible from the PAG WRF, in pit sumps and TMF.

During periods of excess water discharges from the TMF surface water pond, the water will be pumped to a TMF buffer pond located immediately north of, and below, the eastern side of the TMF embankment and then from this pond by gravity flow to the Chilloroya River. Such discharges, when required, will only take place during the wet season, which is between December and April. Results of the current water quality analyses and water balance modeling indicate that during these periods, when runoff flows into the TMF are higher, no water treatment will be necessary. The excess water removal system will be provided with instrumentation to monitor water levels and water quality and releases will only occur upon confirmation of adequate quality.

1.9.2 Water balance

A site-wide process water balance model was developed for the project. This model evaluates the amount of stored water in the various components of the mine, as well as water inflows and outflows between the mine facilities on a monthly basis throughout the life of mine. The main objectives of the process water balance are to provide operating guidelines, design flows, and information inputs for the design of various water management facilities. The results also provided input to the environmental management plans for the project.

Specific key objectives of the site wide water balance together with results are:

 Evaluate the range of normal operating volumes for the TMF surface water pond; this information is used to determine the pond configurations throughout the life of the facility. The predicted normal operating volumes for the TMF surface water pond vary between 1.8 and 3.3 Mm3.

 Evaluate the maximum potential volume for the TMF pond above its normal operating volume to reflect conditions of extreme precipitation; this information is used to establish the minimum required freeboard heights for the TMF embankment at any time. The maximum operational volume for the TMF surface water pond may reach approximately 3.7 Mm3 after a 100 year/24 hr precipitation event.

 Evaluate the amount of water to be discharged from the TMF surface water pond to the Chilloroya River via the TMF buffer pond; this information provides the design criteria for the discharge facilities as well as for the analysis of any downstream environmental impacts and mitigation plans. Under extreme precipitation conditions the amounts of water discharged via the TMF buffer pond may reach up to 3000 m3/hr. These discharges will occur only during the wet season and after adequate water quality has been confirmed.

 Evaluate flows reporting to the PAG WRF containment pond to determine the required capacity of the containment pond and the pumping recirculation rates under conditions of extreme precipitation. The capacity of the containment pond is 600 000 m3 below a freeboard of 4 m, or 800 000 m3 at the pond crest. Pumping requirements for recirculation under extreme conditions may reach 1100 m3/hr.

 Evaluate approximate flows from the in pit sumps and PAG WRF containment pond to determine the needs for treatment at the process plant, as well as the pumping requirements. Normal operating flows from the in pit sumps are expected to be 0 to 400 m3/hr and from the PAG WRF containment pond are expected to be 100 to 800 m3/hr, due to seasonal fluctuations. Maximum operating flows are expected to be between 1200 m3/hr and 1800 m3/hr respectively.

 Evaluate the amounts of fresh water from the pit dewatering wells to the operating system. Operating flows expected from the dewatering wells are expected to be at least 330 m3/hr.

1.9.3 Non-process water

Contact water

Non-process contact water includes water that has been in contact with areas that generate sediment loads and/or requires treatment before it is released. Diversion channels will be constructed to convey contact water to designated ponds or treatment areas. Contact water with sediment loads will be directed to sediment ponds before being released to natural drainages; these ponds include the pit

sediment pond, the main sediment pond, the plant construction sediment pond:, and the crusher sediment pond.

Contact water that will require additional treatment will be managed as follows:

 Plant contact water: during operations, water in contact with the plant area will be directed to a dedicated plant contact pond. From this pond, water will be directed for treatment before it is released to a natural drainage, or alternatively it will be directed to the mill process pond. Contact and non-contact water channels will be constructed around the plant to reduce the amount of water directed to the plant contact pond.

 PAG WRF contact water: water in contact with the PAG WRF will be directed to the PAG WRF containment pond and will not be released to the environment. Excess water such as water from extreme precipitation events, will be recirculated onto the WRF. To reduce erosion and sediment loads, temporary diversion channels will be constructed as the PAG WRF is expanded.

Non-contact water

Non-contact water will be directed around the mining facilities via non-contact water channels from and to natural drainages. Two non-contact water channels are currently contemplated, one upstream of the PAG WRF and the other upstream of the pit.

All water channels will be lined for erosion protection with HDPE geomembrane (temporary channels) or rip-rap (permanent channels). The channels have been sized based on average surface runoff volumes and flows, as well as the 100 year storm event. Sufficient freeboard will be included in the permanent channels to contain flows associated with a 500 year storm event.

1.10 ENVIRONMENTAL AND SOCIAL CONSIDERATIONS