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2013-04-25_REVISION - C1981019
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2013-04-25_REVISION - C1981019
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Entry Properties
Last modified
8/24/2016 5:19:50 PM
Creation date
4/26/2013 8:16:22 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981019
IBM Index Class Name
Revision
Doc Date
4/25/2013
Doc Name
Adequacy Letter
From
DRMS
To
Colowyo Coal Company
Type & Sequence
TR95
Email Name
RDZ
DIH
Media Type
D
Archive
No
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DIVISION OF RECLAMATION, MINING AND SAFETY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866 -3567 <br />FAX: (303) 832 -8106 <br />STATE OF COLORADO <br />COLORADO <br />ID IV I S I O N O F <br />RECLAMATION <br />MINING <br />SAFETY <br />John W. Hickenlooper <br />Governor <br />April 25, 2013 <br />Mike King <br />Executive Director <br />Mr. Tony Tennyson <br />Loretta E. Pineda <br />Colowyo Coal Company Director <br />5731 State Highway 13 <br />Meeker, CO 81641 <br />Re: Colowyo Mine, Permit No. C- 1981 -019, TR -95 Adequacy Review <br />Dear Mr. Tennyson: <br />Regarding your fourth adequacy letter response (dated April 23, 2013), I have the following <br />comments. The Division's decision on TR -95 is no longer pending answers to any of the <br />questions or comments from previous adequacy letters, and no further response is required of <br />Colowyo Coal Company on the revision. The headings correspond to the comment numbers in <br />previous adequacy letters. <br />COMMENT #1 <br />Previous response was adequate. <br />COMMENT #2 <br />Colowyo is correct in the assumption about the Division's error. In our July 2, 2012 letter, we <br />did mean to state `B soils" rather than "C soils." Thank you for pointing out this error. <br />Colowyo states that in the past "SEDCAD modeling overestimated actual flows witnessed at <br />Colowyo Mine." What is this assertion based on? Does Colowyo have flow data or other <br />information to confirm this? It has been the Division's belief in the past that the models have <br />underestimated flows. This was part of the impetus for TR -73. <br />Colowyo's Response: <br />Colowyo's experience has been that under storm event conditions that are not short <br />duration /high intensity events, the model predicts a much greater volume of runoff generation <br />than is witnessed as inflow into the ponds. This suggests that Colowyo's reclaimed areas are <br />intercepting and holding a much greater volume of precipitation than the modeling parameters <br />assume. This phenomenon held to be true utilizing the curve numbers in place prior to the <br />approval of TR -73. Colowyo is required by regulation to design sediment control /stormwater <br />control structures to treat and process the resulting runoff for various defined storm events for <br />10 year, 25 year, and 100 year 24 -hour events, depending on their purpose and intended use. <br />There are many instances when a set of storm conditions can generate stormwater volumes that <br />exceed the design capacities of these structures, and the modeling itself bears this out. This was <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines <br />
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