2013-10-30_REVISION - M1977310 ‎(3)‎

• Permit No: M1977310
• IBM Index Class Name: REVISION
• Doc Date: 10/30/2013
• Doc Name: DRAINAGE DESIGN PLAN FOR THE JD6 MINE
• From: COTTER
• To: DRMS
• Type & Sequence: AM1
• Email Name: TC1
• Email Name: SJM
• Media Type: D
• Archive: No

JD -6 Mine — Drainage Design Plan 11
Table 5. Runoff Curve Numbers for Arid and Semi -Arid Rangelands
(Table 2 -2d of TR -55 [NRCS, 1986])
Cover Description (')
Curve Numbers for
H drolo is Soil Grou
Cover Type
Hydrologic
Condition
A
B
C
D
Herbaceous - mixture of grass, weeds, and low- growing brush,
with brush the minor element
Poor
80
87
93
Fair
71
81
89
Good
62
74
85
Oak- aspen— mountain brush mixture of oak brush, aspen,
mountain mahogany, bitter brush, maple, and other brush
Poor
66
74
79
Fair
48
57
63
Good
30
41
48
Pinyon-juniper—pinyon, juniper, or both; grass understory
Poor
75
85
89
Fair
58
73
80
Good
41
1 61
71
Sagebrush with grass understory
Poor
67
80
85
Fair
51
63
70
Good
35
47
55
Desert shrub —major plants include saltbush, greasewood,
creosote bush, blackbrush, bursage, palo verde, mesquite, and
cactus
Poor
63
77
85
88
Fair
55
72
81
86
Good
49
68
79
84
Gravel Road
76
1 85
89
1 91
Notes:
(1) Based on average runoff condition, and la, = 0 2S.
(3) Poor. <30% ground cover (litter, grass, and brush overstory).
Fair: 30 to 70% ground cover
Good: > 70% ground cover.
(3) Source for gravel road CN is Table 2 -2a of TR -55 (NRCS 1986)
Table 6. Runoff Curve Numbers for JD -6 Mine
Description CN
Pinyon juniper, grass understory, fair condition, Group C soils 73
Gravel road, Group C soils 89
Disturbed ground, mine facilities area 85
4. STORMWATER ROUTING
Stormwater management at the JD -6 Mine focuses on the area of the mine facilities within Sub -basin 132
(shown on Plate 1). Stormwater from upslope is diverted around the mine facilities, as described in Section
4.1 below. Stormwater within the mine facilities area is collected in ditches and/or routed to the
stormwater and sediment retention pond, as described in Section 4.5.1 below.
4.1 Sub - Basins Reporting to Upper, Middle, and Lower Diversion Structures
Three main diversion structures currently exist to divert upslope, non - contact stormwater away from mine
facilities. The Upper and Middle diversion structures intercept runoff from upslope and convey it eastward
into an adjacent sub -basin. As shown in Figure 1, three sub -basins contribute runoff to the Upper
Diversion Structure (UDS). These sub -basins (N -A through N -C) range from 0.71 to 52.4 acres in size
(Table 7). In addition, the UDS extends approximately 60 feet into the adjacent sub -basin and a small
fraction of the adjacent sub -basin (0.033 acres) reports to the UDS.
4148A.131028 Whetstone Associates