REV102573

• Permit No: C1980006
• IBM Index Class Name: Revision
• Doc Date: 4/28/1994
• Doc Name: MR 17 TO MODIFY THE DESIGNS FOR POSTMINING DITCHES B-1 & B-2
• From: TERRA MATRIX
• To: DMG
• Type & Sequence: SL1
• Media Type: D
• Archive: No

TerraMatrix 999 ~~~~,~~F
Engineering S Environmental Services ~~''"
1475 Pine Grove Road • PO Box 774018 ~ ~' ~~ hhn
Steamboat Springs, Colorado (10477 era/S
303-879-6260 • fax [phone] & GeO,~
~~ -UED
April 28, 1994 ~~l!t~'
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Mr. Randall P. Price Q,;,
Division of Minerals and Geology ~~ ,C,d'S ~ e01p9Y
1313 Sherman Street -Room 215
Denver, Colorado 80203
Re: Kerr Coal Company -Marr Mine (Permit No. CO-80-006), Minor Revision MR-17 to
Modify the Designs for postmining Ditches B-1 and B-2
Dear Mr. Price:
Accompanying this transmittal is revised design information for postmining Ditches B-1 and B-2
for Kerr Coal Company's (Kerr) Marr Mine. The revised designs reflect reduction of ditch
width consistent with practical construction constraints and applicable regulatory design
requirements. Kerr respectfully requests that the Division of Minerals and Geology (DMG)
review and approve the revised designs as a minor revision to Kerr's existing approved permit
(Permit No. CO-80-006).
In conjunction with the recently submitted request (3/15/94) for partial bond release for the
Marr Mine, Kerr Coal Company (Kerr) completed a comprehensive review of current approved
reclamation plans and designs to verify consistency between the approved reclamation plans and
the "as-built" configuration and features of reclaimed areas. With one exception there was good
correlation between the actual reclaimed configuration and features and the approved
reclamation plans and designs. The noted exception was in the as-built configuration of
postmining Ditches B-1 and B-2 which are designed to intercept runoff from upgradient areas
and convey it across the reclaimed 720 Pit area to Pond B.
During backfilling and grading of the 720 Pit it became obvious that construction of Ditch B-2,
as originally designed and approved with a 10 foot bottom width and 3H:1V sideslopes, would
be difficult and could result in the potential for ditch or slope instability in the area where the
ditch traverses the regraded slope on the west side of the 720 Pit. Kerr, therefore, requested that
TerraMatrix review the ditch design to determine if overall width could be reduced whip still
effecting compliance with applicable regulatory and engineering design requirements. Design
review resulted in a determination that since the contributing drainage area is less than one
square mile (65.4 acres for Ditch B-2 and 111.7 acres for Ditch B-1), the designs can be based on
the 10-year, 24-hour rather than the 100-year, 24-hour storm event consistent with Rule 4.05.3(3)
and modification of the designs for both Ditch B-2 and downgradient Ditch B-1. In reviewing
and comparing the recently completed reclaimed configuration with the approved reclamation
plans, Kerr discovered that, through an apparent oversight, the revised ditch designs had not
been submitted and approved. This transmittal is, therefore, intended to correct this oversight.
You should also note that given the permanent nature of the subject ditches, Kerr plans to
install a riprapped road crossing in lieu of a culvert where Ditch B-2 crosses the existing road.
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