APPCOR11636

• Permit No: C1981041
• IBM Index Class Name: Application Correspondence
• Doc Date: 4/27/1981
• Doc Name: PRELIMINARY ADEQUACY REVIEW FN C-041-81
• From: MLR
• To: GEX COLORADO INC
• Media Type: D
• Archive: No

Page Thirteen
Preliminary Adequacy Review
GEX - Roadside 5 Cameo Mines
April 27, 1981
4.03.2(4)(3) Culverts and Bridges
Culvert Designs: The use of Mannings equation of Conveyance Factor methodology
is inappropriate for drainage culverts. These methods do not account for
the headloss inherent in the design. GEX must use closed conduit hydraulics
to design the culvert system.
4.05.6 Sedimentation Ponds
LISLE: GEX has used C values from SCS publication Technical Note 50,
figure 7. This figure is inappropriate for disturbed watersheds. Values
for disturbed watersheds are more likely to approximate values given in
Table 5. 4, page 202, Hydrology and Sedimentology of Surface Mined Lands by
Barfield and Haan (1978). In areas where C values change, e.g., refuse piles
and undisturbed rangeland, C values may be area weighted. GEX must use C
values in LISLE calculations which are either obviously conservative or derive
them from applicable tables or figures.
Spillway Designs: The use of Mannings equation for sediment pond spillway
design is inappropriate. As the spillways for several of the ponds are drop
inlet CMP a stage discharge relationship for changing controls (wier,
orifice, pipe) must be used (4.05.6(3)(d)).
_ Y
Dewatering Devices: Several of the ponds have no means of dewatering. As
per Rule 9.05.6(3)(c) all ponds must have a dewatering device.
Detention Time: GEX must address the question of detention time in each
of their ponds in order to evaluate the likelihood of the effluent limitations
(4.05.2(7)) being met.
Sediment Cleanout: GEX has stated that they intend to remove accumulated
sediment every three (3) years. As this represents the entire sediment
storage volume for the ponds this maintenance schedule is unacceptable. GEX
must propose a more acceptable maintenance schedule. The Division would
prefer a maintenance schedule which calls for sediment removal when 60~
of the sediment storage volume is filled or before. A permanent marker placed
at the approved cleanout level in the ponds would assist the operator and
insper_tion personnel in providing proper maintenance.
Short Circuiting: Pond 3 at ti.e Railroad Spur has an inlet very close to
the outlet spillway. GEX must either redesign the pond or provide sufficient
baffling to prevent short circuiting 4.05.6(6).
4.10 Coal Processing Waste Banks
1. The application must contain the results of geotechnical analysis,
discussion of embankment stability, cross-sections and all other information
required by 9.10 for both the Cameo and Roadside coal processing waste
embankments. A11 pertinent information submitted for approval in 1980 should
be adequate.