2011-05-23_REVISION - C1981019 (2)

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Colowyo Response - PR3 adequacy No. 2 25 May 6, 2011 case scenario for hydrology and sedimentology and has specific questions related to that review later in this letter. CCC states in response to this question, "Later stages in the mine progression will be reviewed in more detail..." That detail is required for all areas within the Collom proposed permit area in the current revision application (PR-03). Please refer to the original question. Colowyo's Response: As described in more detail in response to previous Comment I under Rule 2.05.3(4), Exhibit 7, Item 23 Part A has been substantially revised, and the SEDCAD model has been updated. Please refer to our response to Comment I under Rule 2.05.3(4). 4. Please revise the third paragraph on page 132 to reflect the prediction that there will be limited discharge into the pitwalls. Colowyo's Response: Colowyo believes this statement is accurate as written given the additional evaluation and responses provided with this package. 5. Please use in the calculations of spoil resaturation time a spoil recharge rate, rather than a bedrock recharge rate. A reasonable spoil recharge rate for the Collom area would be 3.1 inches per year, calculated as 18% X 17 inches per year average precipitation. The 18% factor is based on Williams and Clark's (1994) spoil lysimeter study which found that approximately 18% of annual precipitation recharge spoil at a Routt County mine. The annual recharge values used in the submittal (0.2 to 0.35 inches, and 1.1 inches) are less than 7% of annual precipitation in the Collom area and apply to undisturbed bedrock, whose permeability, and consequently annual recharge, would be a fraction of the value for spoil. Colowyo's Response: Please see Colowyo's response to Items I and 2 in Rule 2.05.6(3) (a) Protection of the Hydrologic Balance. 6. To be consistent with the 15% swell factor noted in Table 2.05.6-5, please use in the spoil resaturation calculations a spoil porosity value of 15%, rather than 35%. Colowyo's Response: Swell as used in mining applications is defined as the change in bulk density (moist unit weight, in units such as lbs/cu ft) as a result of excavation from in place material to dumped or stockpiled material. The swell factor itself is strictly a volumetric parameter, and is independent of unit weight or porosity. A uniform value of 15% is used throughout this submittal. Porosity is a junction of unit weight, mineral specific gravity, and moisture content. Unit weight or bulk density is affected by swelling (reduces) as a result of excavation simply because the volume occupied by a given mass of soil has expanded. If in place unit weight is know (called moist unit weight or bulk density) and swell percent is known, the bulked (swelled)- unit weight can be calculated as in place density divided by (I + swell %). For example, if the