2017-03-23_PERMIT FILE - C1981019A

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RULE 2 PERMITS • 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, Little Collom Gulch, and West Fork of Jubb Creek of the Collom Mine Expansion area indicate that those drainages do not qualify as alluvial valley floors. Specific discussion of the Collom Gulch Valley As noted in the previous 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 `Iles formation 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 these drainages do not qualify as alluvial valley floors. AVF Studies- Gossard Loadout and surrounding areas All the streams/creeks that exit the Collom syncline/Iles formation hogback still exhibit the deep downcutting that originates in the Collom Syncline lands. This downcutting is easily visible in all streams/creeks exiting the hogback and continues for several miles downstream. This downcutting was due to the 1983/1984 mass -wasting event discussed above. The two streams that will be affected by the Collom Mine Expansion are Jubb Creek and Wilson Creek, near the Gossard Loadout. The possibility of any AVF in Jubb Creek was discussed above. As noted, there is no AVF in the Jubb Creek valley north of the hogback. With respect to Wilson Creek, after the creek exits the hogback, a broad valley filled with valley fill materials is encountered. In the area where the Collom haul road Collom — Rule 2, Page 130 Revision Date: 1/6/17 Revision No.: TR -109