2013-08-15_REVISION - C1982057

• Permit No: C1982057
• IBM Index Class Name: REVISION
• Doc Date: 8/15/2013
• Doc Name: Adequacy Response 1
• From: Seneca Coal Company
• To: DRMS
• Type & Sequence: TR80
• Email Name: JLE
• Email Name: SB1
• Media Type: D
• Archive: No

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August 14, 2013
Mr. Jared Ebert
Division of Reclamation, Mining and Safety
1313 Sherman Street, Room 215
Denver, CO 8020 -4
Seneca Coal Compan
RECEIVED
RE: Seneca II -W Mine (Permit C -82 -057) 0 15 2013
TR -80, Adequacy Response 1
DMSIpr! OF RECLAMATION
Mr. Ebert, MINING AND SAFETY
Seneca Coal Company (SCC) has reviewed Technical Revision No. 80 (TR -80) Adequacy
Review (dated August 8, 2013) and is providing the following responses.
SCC has proposed the addition of two culverts (PM -3A and HRC J3A) as supplemental
culverts to assist in conveying design flows, and has not included design information for
those culverts. The omission of design information is appropriate in this case. However,
if at some future date SCC revises the drainage plans to rely on these culverts, design
information would be required.
Response: No response required.
2. SCC provided a SEDCAD Utility Run for Culvert PM -19, using a base flow value of 0.31
cfs. It is not clear how SCC arrived at this base flow value. The approved PM -2 channel
design assumes a flow of 24.10 cfs in a 10 year -24 hour precipitation event. The Division
understands that the purpose of this culvert is to provide a low water crossing for
equipment but needs a better understanding of the design premise to determine if the
culvert will convey the typical base flow without siltation/clogging, which would result in
an impediment to conveyance of the design flow in the ditch. Please provide additional
information on how SCC determined the base flow value to be 0.31 cfs.
Response: What SCC is referring to as base flow is perennial flow that comes from a spoil
spring that comes to surface next to the main channel between PM -2A and PM -213. This flow
has been measured on a regular basis, by SCC's hydrologist, for the past 2 years showing a
maximum one time measurement of 0.31cfs. Since culvert PM -19 will only be used after the
spring runoff flow (assumed 24.1 cfs) has ceased, the only flow in the channel will be an
assumed maximum 0.31 cfs. Any siltation/clogging of this installed 10" pipe will not affect the
integrity of or cause an impediment to conveyance of the design flow in channel PM -2, since the
existing channel has been constructed in significant excess of the 0.8 feet depth approved (> 5.0
feet deep).
Seneca Coal Company • P.O. Box 670 • Hayden, Colorado 81639
Telephone [phone] • FAX [phone]