2018-03-20_PERMIT FILE - C1981019A (2)

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RULE 2 PERMITS are designed to safely pass the runoff from a 10 -year, 24 -hour precipitation event and, where necessary, will be constructed using bank stabilization methods including energy dissipators, sediment traps, and dug outs or a combination of these methods. Drainage culverts will also use energy dissipators at the outlets if necessary so that runoff will not cause additional erosion and subsequently increased total suspended solids (TSS) levels. Detention ponds will be used to detain runoff water from the disturbed areas to allow the TSS to settle out and to attain acceptable concentrations for other parameters consistent with the requirements of the NPDES Permit. Any Small Area Exemptions (SAE'S) employed will be designed to minimize contributions of TSS to the hydrologic balance. Infiltration and percolation of precipitation in the mine area may be enhanced by the reclamation techniques of contour furrowing on hillsides and the continued excellent revegetation success at Colowyo. Infiltration rates for the pre -mined and post -mine condition of the land were presented earlier. Striffler and Rhodes (1981) showed through field measurements, using an intense rainfall simulation, that infiltration capacities of the mulched and revegetated areas were much greater than the pre -mine estimates. Runoff from the revegetated and contour - furrowed areas has been minor to date, as documented by Colowyo Mine personnel. Flows from Streeter Gulch will be moderated with the detention pond. Moderated flows will continue to pass through the historic drainages. Recharge of the limited groundwater systems in the mine will not be inhibited and may be enhanced through the use of the above techniques. Groundwater protection, per se, is not necessary in the permit area as essentially no continuous groundwater system exists. Perched aquifers of limited nature will be impacted only in the mine area property. This water will be evaporated. The quantity of groundwater is minimal as evidenced by the lack of water in test holes and the dry active pit. Protection of water quality will also be maintained at the present variable limits through the use of the reclamation procedures listed above. Groundwater will not be affected as the supplies are minimal. Surface water will not be significantly impacted in the mine area. An ongoing monitoring program is maintained by the Colowyo Coal Company to verify the conclusions in the permit application. Sampling stations are maintained and samples collected in accordance with the water monitoring plan approved by the Division. Refer to the annual reclamation reports for results of the sampling program. Flow volumes in the Goodspring Creek Alluvial Valley Floor may be impacted by the Colowyo Mine through exercise of water rights. However, the impact is expected to be minimal as the water rights used are owned by the Colowyo Coal Company and are not an integral part of any ranching or farming operation. The Colowyo Augmentation Plan will mitigate the effects on any other water rights and will provide for flows downstream of the affected area. Quality of water in Good Spring Creek will not be affected by the exercise of the water rights. As discussed under Hydrologic Balance - Permit Area, changes in flow volumes caused by mining and reclamation operations will be less than the accuracy range of present day flow measuring equipment. In summary, the Colowyo Mine will not significantly affect the hydrologic balance or water quality Rule 2 Permits 2.05 -48 Revision Date: 10/23/12 Revision No.: RN -06