REV14092

• Permit No: C1981022
• IBM Index Class Name: Revision
• Doc Date: 5/6/1997
• Doc Name: SANBORN CREEK MINE C-81-022 TR 29
• From: DMG
• To: BILL CARTER
• Type & Sequence: TR29
• Media Type: D
• Archive: No

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If the ditch will actually end where the symbol ends, flow will be overland through an
undisturbed azea before it reaches the drainage. Please either clarify that the ditch will be
constructed until it intersects the drainage, or provide a plan for routing flows from the ditch
to the drainage.
8. Please provide additional information which will demonstrate that Second Drainage is capable
of carrying the additional flow from the upland diversion ditch without excessive erosion.
9. The two particle size distributions used by OCM in determining the required sediment capacity
of the Pond C include particles larger than those that would be entrained in sheet flow.
Typically, the largest particles entrained in rill or sheet flow aze sand sized, up to 2.5 mm.
The handbook for the SEDCAD+~"" model, which was used for OCM's submittal, indicates
that the input for pazticle size distribution is the erodible particle size. The model does not
account for erosion caused by channelized flows, which would be expected to entrain particles
larger than sand. The particle size distribution used for Pond B is appropriate. Please provide
a similar particle size distribution for the Pond C watershed.
10. Map OXWVF-03 shows Ditch D10 at a 3% slope, and references cross-section B/03.
Cross-section B on OXWVF-03 shows two ditches which do no[ resemble the description of
D10 in the design (triangular with 1:1 sideslopes). Also, the design for D10 indicates the
slope for the ditch is 0.01%. Please make the necessary corrections so that the design and
illustrations are consistent.
11. The designs for the refuse pile collection ditches specify rip rap lining with a 23" D50. OCM
proposes to reduce the D50 to 19" and augment with grout. Grout can degrade causing loss
of integrity of hte rip rap installation. Please provide additional information which further
explains the 4" reduction being offset by grout. A similaz proposal has been made for the
upland diversion at the refuse pile. This also should be further explained.
12. The permit application indicates discharge from Pond C will be routed to an existing 18"
culvert. Should the 100-year, 24-hour precipitation event occur, would the culvert safely
convey all water dischazged from the refuse area? If not, it would appear that overflow from
the pond might damage the railroad track adjacent to the spillway. While it is not a regulatory
requirement that OCM size the culvert for the 100-yeaz, 24-hour event, it might be additional
insurance for OCM in preventing damage to the track.
13. Please provide a detailed plan view and cross sections of Pond C so that the Division can
verify its capacity.
14. What is the spatial relationship between Ditch DIO and the Pond C embankment wall. Is there
potential for the ditch to cut around any portion of the wall?
15. Map E-3214, the Postmining Drainage Plan, does not include a permanent upland diversion
for the existing refuse pile. Please revise the map to include the diversion.
16. Map E-3211 does not include all ditches, berms, and culverts on site. If this map is meant
only to illustrate drainage features associated with TR-79, this should be noted and a reference
to additional maps made. If not, the map needs to be revised to include all drainage
structures. Also, the symbols shown on [he legend aze not applied consistently on the map
(ditches aze shown as blue dots as well as the conventional stream symbol). Please revise the
map to define all symbols used, and to be consistent in their application.
17. OCM proposes the use of berms to divert disturbed area runoff the sedimentation ponds or
other treatment structures. DMG is concerned that berms will not be as effective as ditches,
Bill Caner 2 May 6, 1997