GENERAL35516

• Permit No: C1994082
• IBM Index Class Name: General Documents
• Doc Date: 4/2/1997
• Doc Name: YOAST MINE C-94-082 SEDIMENT POND II
• From: DMG
• To: JIM BURNELL
• Permit Index Doc Type: STIPULATIONS
• Media Type: D
• Archive: No

III IIIIIIIIIIIII III
999
STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman 51., Roam 215

Denver, Colorado 80?03 ~~~~
Phone p03) 866-3567
FA%: (3031 872-8106
DEPARTMENT OF
NATURAL
RESOURCES
Roy Romer
DATE: April 2, 1997 eOVefgOf
lames S Lochhead
/
/ Enecmive Director
TO: Jim Burnell rt~chael B. Long
Drvivon Director
FROM: Erica Crosby
RE: Yoast Mine (C-94-082)
Sediment Pond 11
Jim, per Larry's request I reviewed the SEDCAD+ designs for sediment pond 11 to be
constructed at the Yoast Mine. When the Yoast Mine permit was approved, a stipulation was
added to demonstrate that Pond 11 will be located as near as practicable to the disturbed area,
and that the pond embankment has a minimum static safety factor of 1.3. It is my understanding
that [he pond will be located along grassy creek, as originally proposed, due to the number of
landslides in the area.
I reviewed the designs that are currently in the permit in Attachment 13-4 as well as the original
adequacy letter sent to Seneca Coal Company on January 23, 1995. Question number 39 of the
original letter requested that Seneca split the Pond 11 watershed into disturbed and undisturbed
subwatersheds with different Curve Number (CN) factors, change the particle size distribution,
and include a base flow of .017 cfs. On March 14, 1995, Seneca responded by changing the pond
designs to reflect a CN of 85 for the disturbed area and changed the particle size distribution. On
April 27, 1995, the Division requested that a CN of 94 be used in the SEDCAD+ model because
it is more appropriate for freshly graded spoil. It was agreed verbally that a CN of 91 could be
used in the model. On June 19, 1995, Seneca revised the SEDCAD+ model to reflect a CN of 91
for regraded spoil. Based on what is in the permit and the original correspondence, Pond I 1 is
appropriately designed. I do have a few comments that should be passed to the operator;
Stipulation #5 states that the pond embankment has a minimum static safety factor of 1.3.
I am not aware [hat this has been submitted to the Division.
2. In the original adequacy letter (question #39), the Division requested that the operator add
a base flow of .017 cfs. This was not included in the SEDCAD+ model. The only need to
include base flow in the model is if Seneca plans on pumping pit water into the pond under their
current operations, or if there is a natural spring that drains into the pond. Seneca typically