2011-11-28_HYDROLOGY - M1988112 (2)

Home Browse Search

Colorado Division of Water Resources June 23, 2011 Page 4 The following sections describe the historic conditions in each of these areas and the proposed operations as part of this SWSP request. Depletions from West Pit and Alluvial Pumping Ground water wells in the West Pit (Figure 2) extract ground water at a rate sufficient to maintain the ground water elevation at a steady -state water elevation in the West Pit. BMRI also continues to operate two Rito Seco alluvial ground water capture wells (M -32 and M -33, Figure 2) to prevent further downgradient migration of affected ground water. To continue to control the hydraulic gradients and water level elevation in the backfilled West Pit, BMRI will need to pump these wells on a year -round basis. Based on historical operations, BMRI expects that approximately 27 to 31 acre -feet per month (ac -ft/mo) will be pumped on a relatively continuous basis from the West Pit. Appendix A, Table A -1 contains a summary of the monthly volumes historically pumped from either the West Pit or the alluvial aquifer that occurred under the decree in Case No. 99CW057. Under the SWSP, BMRI proposes to continue to pump, treat, and discharge as necessary, using the same methodology that has been used historically. Similarly, as currently allowed under the existing augmentation plans, at times during the growing season, BMRI proposes to pump West Pit and alluvial water to the TMF, where all of the water delivered to the TMF will be fully consumed and will be augmented 100 percent. Because there will be more water management activities in the TMF than there have been historically, there will be some increase in depletive effect that will need to be augmented under this SWSP. BMRI has the necessary augmentation supplies to meet these depletions under the SWSP. Using the values in Table A -1 and the proposed additional water to be delivered to the TMF under this SWSP, Table A -2 shows the average monthly volumes pumped from the West Pit and alluvial wells and the expected deliveries of West Pit and alluvial water to the TMF. In general, water will only be delivered to the TMF during the growing season months, where it will be fully consumed. As Table A -2 shows, BMRI expects to pump approximately 90 ac -ft of water to the TMF in addition to the 38 ac -ft of brine that is routinely pumped to the TMF. The remaining approximately 217 ac -ft of water pumped from the West Pit will continue to be discharged to Rito Seco after treatment. Precipitation and storm water runoff capture at the TMF and at the three ponds located in the vicinity of the West Pit will continue to be augmented according to the procedures in 99CW057. Table A -2 shows the monthly volume historically captured due to precipitation and storm water runoff. Such capture typically results in an augmentation requirement of approximately 25 ac -ft/yr. Therefore, the augmentation requirements for ongoing operations in the mine permit area are approximately 155 ac -ft/yr, as shown in Table A -2. This volume of depletions will need to be augmented.