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 3
Section 3.03.1
For slopes < 9%
LS = (L 172.6)' x (10.8 x sin(S) +0.03)
For slopes > 9%
LS=(L/72.6)' x (16.8 x sin(S) — 0.5)
Where: L = Slope length
S = Slope angle
m = 0.3 for slopes< 3%
0.4 for slopes = 4%
0.5 for slopes > 5% and < 10%
0.6 for slopes> 10%
The slope length and slope angles for the non -mined, adjacent land condition and the reclaimed
condition were determined from the Map 33. The LS factor for each slope length and angle were
determined and then averaged.
LS Factor Table
Length (ft)
Slope (%)
LS Factor
300
10.4%
2.9
400
25%
9.95
700
6%
2.10
580
8%
2.52
Surround mine site ave
4.37
Pre -mine portal ave
3.14
RDA/mine site non -mined ave
(4.37+3.14)/2
3.755
200
28%
7.4
400
10%
3.26
400
2.5%
.50
200
7.5%
1.39
Reclaimed mine site
3.14
The average LS is 3.755 for un -mined, adjacent land and 3.14 for the reclaimed lands.
Cover Management Factor (C)
The cover management factor represents the effects of cover above the ground, ground cover (litter),
root mass, incorporated residue, surface roughness, and soil moisture on soil erosion. No
adjustments were made for root mass, incorporated residue, surface roughness, or soil moisture. The
C factors for the non -mined and reclaimed conditions were determined using information from the
vegetation study done by IME in 2013 and 2014 for Phase II/III bond release. The non -mined area
is represented by averaging the sum of the values for plant cover and litter cover in 2013 and 2014
taken from the RDA reference area, the Portal reference area, and the Old Portal reference area. The
post mine, or reclaimed condition, was determined using the same method but by using the data as
collected from the RDA reclamation, the Corley reclamation, and the Vento reclamation in 2013 and
2014. The cover values were again averaged for the three reclaimed areas. The C factor for the
different vegetation types and cover were determined from Table 8B.2, C factors for Permanent
Pasture, Rangeland, Idle land, and Grazed Woodlands, found in Design Hydrology and Sedimentology for
Small Catebments, Ba>feld Varner and Hayes, 1994. The values utilized are shown on Table 1.