2011-06-20_PERMIT FILE - C1981041

• Permit No: C1981041
• IBM Index Class Name: Permit File
• Doc Date: 6/20/2011
• Doc Name: Soils Loss Comparison Roadside South Portal and North Decline
• Section_Exhibit Name: Tab 14 Appendix 14-12
• Media Type: D
• Archive: No

The Universal Soil Loss Equation will be used to calculate the soil loss from the reclaimed mine site and
the adjacent baseline area to determine if untreated drainage from the reclaimed mine site is contributing
suspended solids in excess of premining levels. The following sediment volume calculation is prepared in
accordance with U. S. Department of Agriculture, Technical Notes, Agronomy Note #50, dated January,
1977. The maps and figures utilized in the USLE calculations are obtained from the referenced Agronomy
Note #50.
USING THE UNIVERSAL SOIL LOSS EQUATION
R (rainfall) factors are assigned by geographical regions based on weather data furnished by the U.S.
Weather Service. R values are based on rainfall amount, time, and intensity. In the mountains, R values
were computed primarily for valley areas and have been increased to account for run -off from snow melt.
The R factor of 20 used for this calculation is derived from an iso- erodent map, presented in the referenced
Agronomy Note #50, and is the same for both the reclaimed slopes and the adjacent natural slope.
K (soil erodibility) factors are assigned to each soil series and they are used to predict the erodibility of a
soil and its tolerance to erosion in relation to specific kinds of land use and treatment. Soils having the
highest K value are the most erodible. The K value used for this calculation is picked from the U.S.
Department of Agriculture Soil Survey, Douglas Plateau Area, and is based on the soils classification;
Torriorthents. The K factor of 0.37 is the same for all three south portal areas.
LS (length and percent slope) factors account for the length and percent slope. These factors are taken from
Figure 4. Length of slope begins at the top of the micro watershed. This is usually at the top of a hill, ridge,
terrace or diversion. The length of slope is considered to end for a given field at one of the following
places: (1) the point where the slope decreases to the extent that deposition occurs, (2) the point where
runoff enters a well- defined channel, gully, terrace or diversion , or (3) where water leaves the field. The
LS for the Roadside Refuse Disposal Area is defined by the length and slope gradient of the lowest bench.
The two upper benches are excluded because the run -off encounters a bench where the slope decreases to
the extent that deposition occurs.
Shadscale Reference Area - LS Factor
The LS factor for the Shadscale Reference area is based on an average 2.1 H:1 V Slope and an average
vertical height of 166 feet and average length of slope is 347 feet based on five flow lines located in the
reference area. The length of slope of run-off from the reference area was reduced to a length of 91.2 feet
to make it comparable to the roadside refuse disposal area.
Average Length 91.2 Feet
Average Slope 47.6%
Percent Slope (S)
40.0% 47.6% 50.0%
80 11.000 14.800 16.000
91.2 "LS" Factor 15.920
100 13.000 16.800 18.000
Roadside Refuse Disposal Area - LS Factor
The LS factor for the Roadside Refuse Disposal Area is based on an average 2.22HAV slope at an average
vertical height of 40.3 feet based on seven flow lines cut along the lowermost bench.
Average Length 91.2 Feet
Average Slope 44.2%
Percent Slope (S)
40.0% 44.2% 50.0%
80 11.000 13.100 16.000
91.2 "LS" Factor 14.222JI
100 13.000 15.100 18.000
Roadside Refuse Disposal Borrow Area - LS Factor
The LS factor for the Roadside Refuse Disposal Borrow Area is based on an average 16.1 H:1 V slope at an
average vertical height of 21 feet based on three flow lines cut through the borrow area.
Average Length 343.0 Feet
Average Slope 6.1%
Percent Slope (S)
6.0% 6.1% 8.0%
300 1.200 1.230 1.800
343.0 "LS" Factor 1.316JI
400 1.400 1.430 2.000
TR-61 A14 -12 -2
03/11