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Alluvial Valley Floors - Sudduth Draw - Findings The proposed surface coal mining operation would not interrupt, discontinue, or preclude farming on an alluvial valley floor. None of the proposed mining operations would be .located within the alluvial valley floor. The final mining activities in pit three would be located immediately adjacent to the alluvial valley floor. A buffer would be left along Sudduth Draw, according to Map 15a no mining activities would enroach upon the AVF. 2. The proposed operations would not materially damage the quantity and quality of water in surface and subsurface water systems that supply those alluvial valley floors or portions of alluvial valley floors. Mining in the Sudduth Draw watershed would affect the quantity and quality of surface water supplied to the alluvial valley floor as described in the applicant's statement of probable hydrologic consequences (p. 780-123 to 780-126jjjjj). Mining would reduce surface flow in Sudduth Draw by approximately 3Y, of the annual yield. The ion balance of the surface water could be altered, and salt loading on the stream could be increased by 2.7 kg/yr. These changes do not represent a significant change in surface waters quantity or quality. As discussed in the summary of probable hydrologic consequences, the effects are temporary and would be mitigated by reclamation. 3. Surface coal mining and reclamation operations would be conducted to preserve throughout the mining and reclamation process, the essential hydrologic functions of the alluvial valley floor. Mining operations would not physically disturb the alluvial valley floor. Minor changes in surface water supplied to the alluvial valley floor (as discussed above) would occur during the mining phase of the operation. With successful reclamation and removal of the sediment control system, the quantity and quality of surface flow supplied to the AVF would return to natural conditions. The applicant has suggested that the release of sediment deficient waters from the sediment ponds would cause downstream erosion. Should this occur, the erosion would begin immediately downstream from the sediment pond on Sudduth Draw. Given the infrequent nature of runoff in this area, this erosion, as it occurs, should not be so severe as to affect the essential hydrologic functions of Sudduth Draw. The potential for erosion could be minimized if water from the mine pit is not discharged to Sudduth Draw. 4. Ground Water and Sub-irrigation in Sudduth Draw The alluvium of Sudduth Draw is recharged during snowmelt and precipitation events when this intermittent stream is flowing. The stock ponds located along Sudduth Draw provide sufficient detention time to increase recharge and to sustain sub-irrigation for longer periods of time.