2010-10-01_REVISION - C1981010 ‎(5)‎

• Permit No: C1981010
• IBM Index Class Name: REVISION
• Doc Date: 10/1/2010
• Doc Name: Bond Release Application
• From: Trapper Mining Inc.
• To: DRMS
• Type & Sequence: SL12
• Email Name: RDZ
• Media Type: D
• Archive: No

For post-mining blocks, the USLE is calculated as:
Acpost) = (R)(K)(LSXC)(P)
= (30X.25)(6.2)(.010X1.0)
= 0.47 tons per acre per year
R 30 SCS Map of R factors for Colorado
K 0.25 Trapper Permit C-81-010 Appendix Q
LS 6.2 SCS LS table; 510 feet, 15.7%
C 0.010 SCS C factor for Permanent Pasture, Rangeland, Idle Land,
and Grazed Woodland - no canopy, 85% herbaceous cover,
grass type (Table 1.2-1 of Bond Release submittal)
P 1.0 SCS P factor
The USLE demonstrates that the existing condition of the reclaimed blocks results in equal or lesser
sediment contributions to surface runoff as compared to pre-mining conditions on an annual basis.
1.4.2 SEDCAD 4
Trapper has developed a site drainage and sedimentology model to estimate the total quantity of
sediment produced from a storm event for the runoff from each block under pre-mining and post-mining
conditions. The block drainage and sedimentology models were developed utilizing SEDCAD 4 for
Windows, a computer software program developed to assist in the evaluation of stormwater runoff,
erosion, and sediment control management techniques.
To develop representative models of the pre-mining conditions in each block, baseline information from
the permit was utilized as input data in the SEDCAD 4 program. To develop comparative models
representing existing conditions for each block, the vegetation survey information outlined in Section 1.2
was utilized as input into the SEDCAD 4 program with input parameters modified as appropriate in
accordance with this information. Given the irregular shapes of the blocks in relation to the topography
and recognizing that portions of individual blocks may fall within adjacent sub-watersheds, it is difficult to
develop specific pre and post-mining runoff models for each entire block. In order to develop
representative and comparable runoff models, typical twenty acre sections of each block were modeled
using the average slope and slope length for the entire block. A summary of the SEDCAD 4 program
inputs and results for both the pre-mining and post-mining land conditions are shown on Tables 1.4-1 and
1.4-2 respectively. The SEDCAD 4 computer printouts and input calculation sheets can be found in
Appendix 3. Input parameter references are also provided in Appendix 3.
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