2015-10-06_PERMIT FILE - C1981019 (14)

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RULE 2 PERMITS Other Potential Impacts Flooding and stream flow regime do not appear to have been affected by past mining operations or reclamation, nor are they anticipated to be affected by Collom Lite and Little Collom X mining. Groundwater availabilit- in the area may potentially be enhanced with the storage of water in the reclaimed pits. Colowyo owns significant water rights within the affected drainages. Any potential diminishment of flow will be compensated for by reduced use by Colowyo. There is sufficient capacity for Colowyo to reduce their use of adjudicated water to compensate for potential diminishment of flow, allowing downstream users full access to their water rights. With respect to alluvial valley floors (AVFs), lower portions of Collom Gulch have been studied before and since the release of the 1985 OSM Alluvial Valley Floor (AVF) Reconnaissance map. The reconnaissance by OSM was compiled on 1:100,000 -scale maps and was meant to represent a reconnaissance level effort to identify areas which are likely to meet the AVF definition (from Introduction to OSM report accompanying this study). Thus, any area identified on the OSM maps are potential AVFs. It was recognized in this study that future studies may more conclusively prove or disprove the AVF findings in the report. Colowyo and other companies in this area performed AVF studies to more conclusively prove or disprove the existence of AVFs in this potential coal mining area of the Danforth Hills. For the Collom area, there has been significant studies to date examining the Collom Gulch and the otp ential for an AVF in the area possibly affected by mining activities in the Collom light area. As noted in the previously submitted text, alluvial materials are present in the valley bottoms of the Collom Gulch drainages but the materials are intermixed with significant fractions of colluvium and sheetwash from adjacent slopes. This can be seen in the geologic description of the monitoring well (MC- 04 -02) in the lower portion of Collom Gulch in Section 24, T. 3 N., R. 93 W. The cuttings obtained from the drill hole are predominantly silty clays, with minor amounts of sand and gravel ( <25 %). Based on depth to groundwater in this drill hole (10 feet below ground surface), it is doubtful that subirrigation of any plant crop is possible. Further to the north, near the confluence of Collom Gulch and Little Collom Gulch, monitoring well MLC- 04 -01, has a ground water level of between 40 and 50 feet below ground water surface. In addition, active erosion in the Collom Gulch channel is causing further incision, which is lowering the unconfined groundwater table found in the valley. The incision in Collom Gulch is at least two feet and in excess of 20 feet in sections before that flow of Collom Gulch exits through the `hogback' and flows onto the Mancos Shale located in the Axial Basin to the north. The incision is also widening due to the downcutting and erosion of the supporting banks during periods of higher flow (normally occurring during the spring). With the low surface water flow rates and the reduced flood frequency, this has reduced the ability of the valley bottoms to support any agricultural use other than rangeland. Local and regional agricultural economics are prohibitive to developing irrigation projects within these valley bottoms, and such practices are in decline locally, especially on such a small scale as would be required by the narrow and fragmented nature of irrigable bottomlands within the subject drainages. The narrow width and fragmented nature of the minimal flat land, depth to ground water, and impracticality of economically irrigating or mechanically farming the valley bottoms within Collom Gulch indicate that those drainages do not qualify as alluvial valley floors. Collom — Rule 2, Page 142 Revision Date: 9/28/11 Revision No.: PR -03