2011-07-01_PERMIT FILE - C1982057A ‎(3)‎

• Permit No: C1982057A
• IBM Index Class Name: Permit File
• Doc Date: 7/1/2011
• Doc Name: Shrub Plot Slide Remediation Plan
• Section_Exhibit Name: Tab 20 Attachment 20-D
• Media Type: D
• Archive: Yes

• j0 rtn try est c.olorado Consultants Inc.
eotechnical /Environmental Engineering •Materials Tescing
October 28, 2010
Seneca Coal Company
P.O. Box 670
Hayden, CO 81639
Attn: Roy Karo
Job Number: 08 -8099
Subject: Site Observations and Slope Stabilization
Recommendations, Pond 016 Area Slides, Seneca IIW
Mine, Routt County, Colorado.
Gentlemen,
As requested by our client, Seneca Coal Company (Seneca), NWCC, Inc. (NWCC) has completed this report to
summarize our observations made of the landslides /slope failures that have occurred in the Pond 016 Area at the
Seneca IIW Mine in Routt County, Colorado. The subject landslides are located uphill (east - northeast) of Pond 016,
uphill (east - southeast) of Pond 016A, and downhill (west- northwest) of the Shrub Plot. A plan showing the existing
. conditions in this area is provided in the Pond 016 Area Remediation Plan Existing Conditions, Exhibit No. 20 -D.1,
Sheet 1 of 1 provided in Appendix C.
This report provides additional recommendations for stabilizing and dewatering the landslide area located upslope of
Pond 016, as well as recommendations for stabilizing the failed areas situated upslope of Pond 016A and downslope of
the Shrub Plot. These recommendations are based on the conditions observed at the site as of this date, the Pond 016
Area Remediation Plans dated October 2010, and the recommendations provided in the Geotechnical Evaluation and
StabilizationlReconstruction Recommendations report previously prepared by NWCC for the Pond 16 Landslide and
dated August 3, 2009.
Pond 16 Landslide - Site Observations: NWCC visited the project site on several times in August and September
2009, and May 2010 to observe the test trench/pits (trenches) being excavated to the east/northeast of the Pond 16
Landslide, as well as to take additional groundwater level measurements from the monitor wells installed within and
above the landslide area.
Based on our observations made at the site in 2009, it appeared that the extreme upslope (northern) ends of the trenches
had been advanced through the natural clays and into the underlying weathered claystone materials. A moderate
amount of groundwater seepage was encountered at the northern end of the eastern trench and only a slight amount of
groundwater seepage was encountered at the northern end of the western trench/pit. The groundwater was collecting in
the base of the trenches and then being diverted into Pond 016. It should be noted that the remaining portions of the
trenches /pits had been excavated through the fill materials and into the natural clays that are overlying the weathered
bedrock materials.
(970) 879 -7888 • Fax [phone]
2580 Copper Ridge Drive • Steamboat Springs, CO 80487