PERMFILE46723

• Permit No: M1988112
• IBM Index Class Name: Permit File
• Doc Date: 11/8/1988
• Section_Exhibit Name: APPENDIX Q ADEQUACY REVIEW QUESTIONS AND RESPONSES
• Media Type: D
• Archive: No

r 53. Please provide peak flow calculations for the South Waste Rock Disposal
Facility haul road culvert.
t Response: These calculations are provided on Table D.9-2. A WASHED printout
for this drainage area has been added to Appendix G.
Table D.9-2 and Appendix H revised 2/15/89.
54. A headwater-to-diameter ratio of about 2 was used in sizing culverts.
This design is acceptable if the downstream face of the embankment and
a sufficient )ength of channel bottom are armored with riprap. A design
for riprap size and extent should be submitted. The riprap
specifications required for the low-velocity drainage swale on the
river haul road crossing should also be included.
Response: Riprap design calculations are presented in Appendix L' for the
culvert outlets at the South Waste Rock Disposal Area Haul Road
Culvert and the Rito Seco crossing.
In summary, 12" DSO riprap is proposed for the South Waste Rock
Disposal Area culvert outlet for a length of 35 feet downstream
of the outlet. A 24" thick blanket is proposed for the channel
invert with an ]8" thick blanket over the channel sideslopes.
' For the Rito Seco crossing, 18" DSO riprap is proposed for a
length of 50 feet downstream of the culvert outlet. 36" and 27"
blankets are proposed for the channel invert and side slopes,
respectively.
The calculations are based on a riprap design method presented
in Urban Storm Drainage Criteria Manual (Wright-McLaughlin
Engineers, 1969). Very erodible materials were assumed to exist
in the channels for design purposes. Figure D.9-3 showing typical
riprap outlet protection has been adder to Section D.9. The
material used will be run of mine material placed using mine
equipment.
' Exhibit D, Section D.9 revised 2/15/89.
55. It appears that no erosion control/runoff control measures have been
1 established for the mill and concentrated ore stockpile areas. Please
locate a small ditch/bean similar to a roadside ditch, sized to the 10
year, 24-hour flow, around the perimeter of both areas.
j Response: The details of drainage within the mill site area are part of the
detailed mill site plans which are being developed by others and
_ have not been completed. Details of the mill site drainage will
' be provided upon completion of the mill design.
Exhibit D, Section D.9.2 revised 4/20/89.
56. Pease explain what is meant by "Geotextile (6" and 12" minimum cover)"
in Typical Profiles (A-A'J and Typical Cross Section (B-B') in Figure
D.9-2.