HYDRO22971

• Permit No: C1981012
• IBM Index Class Name: Hydrology
• Doc Date: 4/5/1991
• Doc Name: MEMO NEW ELK MINE WASTE PILE UNDERDRAIN DESIGN PN C-81-012
• From: MLRD
• To: BERHAN KEFFELEW
• Permit Index Doc Type: CORRESPONDENCE
• Media Type: D
• Archive: No

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999
STATE OF COLORADO
MINED LAND RECLAMATION DIVISION

Department of Natural Resources of ~o
,~~.=~t~Ry
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1313 Sherman St., Room 215
Denver, CO 80203
Nei%
303 866-3567
FAx: [phone]
Roy Romer,
Goverwr
DATE: April 5, 1991
T0: Berhan Keffelew
FROM: Jim Pen dl eton
RE: The New E roe's ste Pile Underdrain Design
it No: C-81-012)
Fred R. Banta.
Division Director
In response to your recent request, I have reviewed the permit documents for
the New Elk Mine's coal refuse disposal structure. You have indicated the
receipt of a ten day letter from the OSMRE questioning the design of the
structure's underdrain.
The application design documents depict an 8' x 16' rods underdrain, as
required by the regulations in place at the time of its approval. Since that
time the OSMRE regulations have been modified, deleting the specified cross
section area. Figures 5 through 10 within the design document stability
analysis report depict the cross section and longitudinal profiles of the
approved underdrain system.
The New Elk underdrain is intended to serve primarily as an interceptor of
sub grade seepage and percolation through the pile's superstory. The
underdrain is designed to weep into the sediment pond located at the toe of
the refuse pile. I have visited the site at least annually since the pile's
commencement and have never observed flow from the underdrain. Surface runoff
from the pile does collect within the pond.
In ~ experience the 8' x 16' underdrain cross section is grossly oversized
for our semi-arid climatic conditions. The boiler plate requirement, like
many others inherited from the OSMRE regulations, reflects experience in humid
climates in other portions of the USA. Practices such as head-of-hollow fill
construction with chimney drains necessitate large cross-sectional drains
capable of accommodating significant flows. In Colorado we have not
encountered situations reminiscent of these eastern and mid-continent design
situations.
In conducting mineral program mine plan reviews I have occasionally required
the applicant to complete detailed sub drain designs, considering flow
projections, drain siltation and cavitation potential, drain matrix mechanical
strength and abrasion characteristics, etc. Specifically, several large
proposed spent shale disposal piles :sere required to complete detailed design
procedures. Even in those situations, representing piles as large as
300 million cubic yards wish depths of up to 1300' with chimney drains