2016-01-22_REVISION - C1981014 ‎(4)‎

• Permit No: C1981014
• IBM Index Class Name: Revision
• Doc Date: 1/22/2016
• Doc Name: Adequacy Response #3
• From: Gorham Energy Consultants, LLC
• To: DRMS
• Type & Sequence: SL3
• Email Name: RDZ
• Email Name: JRS
• Media Type: D
• Archive: No

Sediment Demonstration — Mine Site - revised 1/22/2016 w/ 1/8/2016 addendum Page 6
Section 3.03.1
Length (ft)
Slope (%)
LS Factor
700
6%
2.10
Demo #1 Post weight RDA
Length (ft)
Slope (%)
LS Factors ave.
500/240
3.4/24.4
4.56
Demo #2 Adjacent areas
Length (ft)
Slope (%)
LS Factors ave.
700/500/200/300
6/6/25/8.3
3.34
Demo #2 Post weight RDA
Length (ft)
Slope (%)
LS Factors ave.
500/240
3.4/24.4
4.56
C factor values specific to the RDA were used. The C factor for the RDA reference area is 0.02136.
The C factor for the RDA reclaimed area is 0.011. Factors for R, K, and P remain unchanged for
reasons previously discussed.
Demo #1 Pre -mine RDA footprint
A=RKLSCP
A = (24.7) (.32) (2.10) (.02136) (1.0)
A =.355
Demo #1 Reclaimed RDA condition
A=RKLSCP
A = (24.7)(.32)(4.56)(.011)(1.0)
A = .396
In this scenario, the results show that the reclaimed RDA individually produces more sediment than
the exact same area in the pre -mine condition. To overcome the influence of the increased LS factor
that result from construction of the approved RDA, the cover values on the reclaimed RDA would
need to be close to 85% cover for the output values to equalize. A summary of the results is shown
in Table 3 below.
Table 3
RDA Annual Sediment Yield
tons/acre/year
Pre -mine RDA footprint .355
Reclaimed RDA Condition .396
However, when calculating the LS factor using the pre mine RDA footprint area and the actual
slopes from the immediate adjacent area that surrounds the RDA, the modeling output changes
significantly. Demonstration #2 uses information from the interpolated pre -mine topography of the
RDA footprint as well as from adjacent, non -mined lands surrounding the RDA area.