2011-11-28_HYDROLOGY - M1988112 (2)

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Colorado Division of Water Resources June 23, 2011 Page 2 This letter presents the proposed operations covered by the SW SP, the accounting for depletions and replacements, and how injury to other water rights will be prevented. BACKGROUND BMRI has historically been engaged in a gold mining and beneficiation project known as the "San Luis Gold Project." The mine permit area is shown in Figure 1. Rito Seco, a tributary to Culebra Creek, flows through the mine permit area (Figure 1). The water rights for this project were adjudicated in Case No. 89CW32 and a modified augmentation plan was adjudicated in Case No. 99CW057 to deal with mine post - closure reclamation issues. BMRI is currently operating under the existing augmentation plans. Under these augmentation plans, as part of its post - closure reclamation plan BMRI pumps ground water in, and near, the backfilled West Pit at the mine site. The general location of the West Pit is shown in Figure 1. The series of wells installed in, and near, the West Pit are shown in Figure 2. Some of the West Pit and Rito Seco alluvial wells are pumped to maintain ground water levels in the backfilled West Pit to prevent ground water outflow into the Rito Seco alluvial aquifer and, in the case of alluvial aquifer wells, to control migration of constituents downgradient in the alluvial aquifer. Water pumped from the backfilled West Pit and from the Rito Seco alluvial aquifer wells downgradient of the West Pit to control migration of ground water in the alluvium has been delivered to an on -site treatment plant, treated, and then discharged to Rito Seco. Historically, BMRI has at times evaporated water rather than treating and discharging it, and has also delivered water pumped from the West Pit to the TMF. When water is managed by these means, the water is augmented 100 percent. There is also a brine concentrate from the treatment process that is not released, but pumped to the TMF. Depletions associated with this operation will continue to be augmented, as has been done historically. According to the 99CW057 decree, pumping of West Pit wells and Rito Seco alluvial wells causes instantaneous depletions to Rito Seco; therefore, any depletions from a) water pumped, treated, and released, b) evaporated, or c) delivered to the TMF will be augmented in the month when the depletion occurs. In addition to West Pit and alluvial well pumping, BMRI also has augmentation obligations related to precipitation and storm water runoff capture at the TMF and the ponds in the vicinity of the West Pit. In Case No. 89CW32, BMRI agreed to replace precipitation and storm water runoff capture at the 192 -acre TMF. A set monthly volume is replaced during the period November through March (4.28 ac- ft/mo), and during the period April through October an amount equal to the surface water runoff that would have occurred from the TMF is replaced (based on runoff curve number 82). In Case No. 99CW057, BMRI agreed to augment all of the storm water runoff captured in the two ponds near the West Pit and the retention pond in the vicinity of the pipeline from the West Pit to the tailings facility. These ponds are shown in Figure 1.