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REV104555
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Entry Properties
Last modified
8/25/2016 1:15:53 AM
Creation date
11/22/2007 1:18:44 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981019
IBM Index Class Name
Revision
Doc Date
10/9/2007
Doc Name
Preliminary Adequacy Review
From
Colowyo Coal Company L.P.
To
DRMS
Type & Sequence
RN5
Media Type
D
Archive
No
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identify what areas are in the process of being backfilled and rough graded and when it has <br />been completed <br />9. Based on field inspections, it appears that Colowyo has completed construction of the <br />Prospect Ditch. Due to concerns (geotextiele and riprap installed) during this construction <br />season, prior to the azea being covered with snow. Additionally, the Division requests that <br />Colowyo provide a certified as-built drawing for the Prospect Ditch to verify that is was <br />completed according to the current approved designs. <br />Response: Colowyo at this time has not completed the construction of Prospect Ditch. However, <br />Colowyo will provide the Division with a file copy of the as-built drawing after Prospect <br />Ditch construction is complete. <br />10. The hydrology, sedimentology and design of Prospect pond have been the subject of <br />much discussion and revision since 1992. It is Colowyo's practice to design ponds for a <br />worst case condition that assumes that various portions of the watershed area in different <br />stages of reclamation after the pit is reclaimed. The design also assumes that during mining <br />operations, when a large pit is in-place, that much of the storm water runoff is captured by <br />the pit. This presumption was accepted by the Division given that both Streeter and Gulch A <br />watersheds reflected this practice. (see 2006 ARR Map). <br />The Prospect pond, as currently approved, also assumes a worst case condition with four <br />varieties of land condition; reclaimed 3 or more years of vegetation growth, reclaimed 1-2 <br />years vegetation growth, lands topsoiled and seeded with no significant vegetation, and <br />undisturbed lands. The latest pond modeling was revised and approved in 2002 for the <br />Prospect Pond. Calculated peak discharge from the modeling resulted in 2.33 cfs with a total <br />runoff volume of 1.95 ac-ft. The Division approved this pond, and subsequent revisions, <br />primazily because of Colowyo's commitment that the actual reclamation on -the-ground <br />would closely mimic the assumptions used in the modeling. Conversely, if actual condition <br />do not, then the logical conclusion would be that the pond will likely not function as <br />designed. <br />The current problem lies in the fact that approximately 320 acres of land in pit, ungraded <br />spoil, and spoil ridges, and final grade B & G lies directly above the Prospect pond. Again, <br />Colowyo is rapidly completing all backfilling and grading of the East Pit with a dragline and <br />dozers. If all of the approximately 320 acres are regraded to f nal grade, the actual field <br />conditions will massively exceed the hydrologic modeling assumptions In a negative way. <br />This could have catastrophic impacts to the lands below, including State Highway 13. <br />The Division believes that it will be difficult for Colowyo to reclaim the Prospect watershed <br />to a condition reasonably close to the hydrologic design assumptions anytime in the next two <br />years without a significant change in the reclamation pace and practices. <br />For example, last year Colowyo completed 86 acres of backfilling and rough grading, <br />topsoiled zero acres, and reseeded 20 acres. At this rate, the East Pit will be at final grade as <br />eazly as late 2007, leaving hundreds of acres of regraded spoil with no topsoil or vegetation. <br />The Division believes that given the current on-the-ground conditions and near future <br />conditions, a small intense storm event than a 10-year recurrent interval (1.8 inches/24 hours) <br />
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