2011-05-04_REVISION - C1982057

• Permit No: C1982057
• IBM Index Class Name: REVISION
• Doc Date: 5/4/2011
• Doc Name: Round 1 Adequacy Review
• From: Seneca Coal Company
• To: DRMS
• Type & Sequence: TR73
• Email Name: SLB
• Email Name: SB1
• Media Type: D
• Archive: No

Pond 016 Slide Remediation Plan
Page 7
the spillway invert height of 7,462.00', but indicates the riser height will be 2.5'. Is SCC
proposing to modify the drop inlet spillway?
Response: SCC is not proposing to modify the drop inlet spillway. The "new" design has been
revised to indicate the existing riser height of 5'.
26 The design submitted for Pond 016 includes the two stock tanks (T-26 and T-27) as
sediment control features. The previously approved language in the permit application
package, on page 11 of Tab 13, indicates that the stock tanks are not primary sediment
control structures. If SCC intends to rely on these structures to control runoff and
sedimentation, the language of Tab 13 will need to be revised accordingly. Also, SCC will
need to submit detailed design information, as required by Rule 4.05.6(5), indicating that
Stock Tanks T-26 and T-27 will comply with Rules 4.05.6 and 4.05.9.
Response: The text on page 11 of Tab 13 is correct; the stock tanks are not primary sediment
control structures. If the SEDCAD design is closely reviewed, it shows that there is no sediment
retention incorporated. These structures were included in the SEDCAD run because they are
currently inplace as an integral part of the drainage system. Any structure constructed in a runoff
channel provides some runoff control by slowing the velocity of runoff at that point.
The Stock Tanks as designed and built have been approved in the permit and do not appear to
require further detailed design information until they are requested as permanent structures as
discussed in Tab 13, Attachment 20-2, Permanent Structures Documentation, page 20-2.5, Stock
Ponds.
27. If the stock.tanks are an integral part of the runoff and sediment control system as
indicated in the proposed Pond 016 drainage area plan, they would need to be maintained
at their design capacity until SCC can make a demonstration, under Rule 4.05.2(2), that
the quality of untreated drainage from the disturbed area meets applicable water quality
standards. Both stock tanks are a considerable distance from LU-6 (T-27 is about 1,500'
away and T-26 is about 500' away). SCC will need to address access to the stock tanks for
maintenance during the period of time that the stock tanks are necessary for sediment
control.
Response: Once again, the stock tanks are not primary sediment control structures. There is no
required design capacity for water retention, only that they cannot retain more than 2 acre-feet of
water at the time they are requested as permanent structures. SCC has not yet requested that
these structures remain as permanent, that determination will be made prior to Phase I bond
release request for the specific locale. If access is necessary, the same cross country route will
be used for ingress and egress. No permanent access is planned.
28. The SEDCAD run for Pond 016 uses a curve number of 71 for reclaimed areas, based on
"good (> 70%) " vegetative cover and a C type soil group. This value appears to be based
on approved input values found in the permit application package, in Appendix 13-5B; the
tables in Appendix 13-5B are derived from NRCS TR-55. The vegetation monitoring
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