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Technical Revision (TR-28) Climax Molybdenum Company Environmental Protection Plan Permit No. M-1977-493 ■ A portion of the Robinson TSF (1 Dam). The Oxide Pond (Eagle Park Reservoir) was first constructed in the early 1960s to impound tailing material from the oxide ore processing facility at Climax. Oxide ore processing was discontinued in 1968. The tailing material and sediments in this TSF were acidic and contained elevated levels of metals. Seepwater emanating from the toe of the dam (4 Dam) likewise was acidic (Appendix G, original 1995 EPP) In 1993, a project was initiated to convert Eagle Park Reservoir to a fresh water impoundment to allow Climax to sell the storage facility. Such a conversion of this impoundment required draining of impacted water, removal of tailing material and contaminated sediments, and prevention of Robinson Lake seepage from entering the impoundment. This project was completed in 1997. Impacted media (water, tailing, sediment, and soils) were removed to the Tenmile TSF and 2 Dam during the course of this project. Eagle Park Reservoir was released from DRMS financial warranty and was sold to a private consortium of downstream users in 1998. Eagle Park Reservoir is no longer within the affected lands boundary of the Climax site. It is not considered an EPF nor is it ever to be used as an EPF or for secondary containment by Climax. The Climax EPFs in place in the upper Eagle River watershed are in fact designed and operated to preclude discharge of impacted water from mine facilities to Eagle Park Reservoir. Robinson Lake is an EPF and functions as the primary process water storage facility in the system. The reservoir stores process water that is collected from the Tenmile and Mayflower TSFs and delivered through the Tenmile Tunnel. Water collected from the Tenmile TSF is decanted through the Tenmile Decant to the Tenmile Tunnel and water collected from the Mayflower TSF is pumped by the Mayflower barge system to the Tenmile Tunnel. Robinson Lake also collects seepwater and toe drain discharge from 1 Dam as well as seepwater pumped from the Robinson Dam and 4 Dam seepage collection systems The reservoir primarily contains industrial process water, TSF seepwater and 4 Dam seepwater, along with unintercepted storm water from the surrounding area and overflow from Chalk Mountain Reservoir. The Robinson TSF is an EPF and was originally constructed in 1936 straddling the uppermost watersheds of Tenmile Creek to the north-northeast and the Eagle River to the west-southwest (Figure AM-06-T-01). The largest dam, the 240 foot high 1 Dam, contains the TSF upstream of Robinson Lake in the Eagle River drainage. 2 Dam is partially inundated by the upstream portion of the Tenmile TSF in the Tenmile Creek drainage. While the tailing material contained within the Robinson TSF consists primarily of quartz silica and orthoclase feldspar, it also contains enough sulfur to be acknowledged by Climax as acid producing. In addition to tailing material, seepage from the Robinson TSF and water discharging from the toe drain system beneath 1 Dam are potential sources of contamination. Tim's Pond and Warren's Pump Station serves as the primary collection system for seepwater from 1 Dam and the Tenmile Tunnel and returns collected water to the SDP via the 2 Dam Pipeline. Robinson Lake acts as a secondary collection system for these co-mingled waters, and the Robinson Lake Pump Station will serve to return this water to the industrial process water circuit for reuse as needed. There are no designated chemicals stored or utilized in the Eagle River watershed. T-5.2.2 Environmental Protection Facilities The following controls are designated EPFs to prevent potential impacts to Eagle Park Reservoir and the East Fork of Eagle Creek from Climax operations: ■ Robinson TSF and 1 Dam; ■ Robinson Lake and Dam; ■ Warren's Pump System; ■ Robinson Lake Seepage Pump System; EPP: Version R4 T-20 August 2018