2011-05-23_REVISION - C1981019 ‎(2)‎

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 5/23/2011
• Doc Name: 2nd Adequacy Response Review
• From: Colowyo Coal Company
• To: DRMS
• Type & Sequence: PR3
• Email Name: JHB
• Media Type: D
• Archive: No

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Colowyo Response - PR3 adequacy No. 2 24
May 6, 2011
the Collom area, there has been significant studies to date examining the Collom Gulch and the
potential 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 ofsand and gravel (<2501o).
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.
Colowyo has amended the text in Section 2.05.6(3) (b) (iii) under the subheading of "Potential
for Spoil Spring Water Discharge Impacting Downstream Areas" to reflect this response.
3. As mentioned previously, the plan for control of surface water drainage through the disturbed
area is deficient at this time due to uncertainty of the proposed mine plan and the long-term
presence of the temporary spoil pile in the center of the disturbed area. The application does
not adequately present how surface water will be handled over the life of the operation (Rule
2.05.6(3)(b)(i)).
The response is inadequate. The application does not adequately present how surface water
will be handled over the life of the operation (Rule 2.05.6(3)(b)(i)). The Division cannot defer
sediment control issues to a later date unless CCC is requesting only limited mine plan
approval for the Collom Lite and Little Collom X areas. The Division understands the worst