2009-09-01_PERMIT FILE - M2009018 ‎(9)‎

• Permit No: M2009018
• IBM Index Class Name: PERMIT FILE
• Doc Date: 9/1/2009
• Doc Name: Request for Continuance
• From: Varra Companies, Inc.
• To: DRMS
• Email Name: MAC
• Media Type: D
• Archive: No

ENVIRONMENTRL SERVICES
CGRS August 28, 2009

Varra Companies
8120 Gage Street
Frederick, Colorado 80516
Attn: Mr. Brad Janes
Subject: Slope Stability Review Response
Heintzelman Pit 116
Platteville, Colorado .
CGRS No. 1-135-10807ab
Dear Brad:
We have reviewed the August 7th Adequacy Review by Division of Reclamation, Mining and
Safety (DRMS) and provide responses to comments by item based on our evaluation. Other
items will be addressed by Varra Companies.
1. The soils at the site generally consist of 5 feet of eolian deposits underlain by sand
and gravel. The average thickness of the sand and gravel deposits is 45 feet, thus a
total excavation depth of 50 feet.
2. Items addressed by Varra Companies.
3. The shear strength parameters assigned in the slope failure model were based on
direct shear test results for soils obtained from the Varra Durham pit, which
documented an internal friction angel of 49 degrees for sand. The test results are
attached as Attachment A. Geologic investigations and mining activities less than
one-half mile from the Heintzelman pit document soil conditions similar to those
encountered at the Durham pit. Meyerhof, 1956 and others document the
relationship of penetration resistance to internal friction angles. This relationship is
provided as a table in Attachment B. Investigations conducted by CGRS in close
proximity to the subject property documented sand and gravel densities as dense to
very dense. The table in Attachment B shows a corresponding internal friction angel
of between 40 and greater than 45 degrees for dense to very dense sand, which was
the basis for our model input. We understand that geologic properties can vary
greatly over short distances; however, we chose to use field data rather than table
values for our analysis. This included geotechnical data for the Pierre shale bedrock.
In summary, we feel the input data used in our analyses are more representative of site
conditions than generic table values. A slope failure analysis using a more conservative
internal friction angle value is attached.
O:Wrojects_ArchivelSite 10000 thru 109991108071Environmenta1110807ab\CorresplHeintzelmanSlopeReply.doc
P.O. BOX 1489 o FORT COLLINS, COLORADO 80522 a PHONE: [phone] FAX: [phone]