PERMFILE102773

• Permit No: M1999098
• IBM Index Class Name: Permit File
• Doc Date: 2/23/2000
• Doc Name: ADEQUACY REVIEW RIVERVIEW RESOURCE M-99-098
• From: TUTTLE APPLEGATE INC
• To: DMG
• Media Type: D
• Archive: No

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Consultants for Land, Mineral and Water
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February 22, 2000
Ms. Christina L. Kamnikaz
Division of Minerals and Geology
1313 Sherman Street, Room 215
Denver, Colorado 80203
,~=CEIVED
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Subject: Adequacy Review - I2iver~ie+v Resources - .#M -99-098
Dear Christina:
G ~ g 2 3 2000
~.,~,,:~ „i nAinerab & Ge01o9Y
In answer to your letter dated January 20, 2000, We have prepazed the following response:
Item #1 -The presence of de-watering trenches aze included in the stability model. The height of
the mined slope is approximately five feet higher than the bore logs indicate the gravel reserve to
be. This is done to account for any de-watering trench that may be necessary. The phreatic surface
shown starts at the toe of the slope and transitions back to the normal ground water surface
elevation as shown in the attached borelogs. This represents a highly conservative estimate of the
phreatic surface found next to a mined gravel highwall with a de-watering trench located at the toe
of the slope.
C
~.~' Item #2 -You have requested that the bedrock andemeath the gravel reserves be modeled with a
,.)` '~ cohesive value of 0. We do not believe this to be a valid assessment of the strength of this material.
~~ ~ The zero cohesive strength is referring to the residual strength of a clay material. This type of
analysis is not appropriate in this case for several reasons:
1. Gravel high walls aze considered to be temporary structures. It can take several years for the
clay material to reach its "residual strength" if at all.
2. The weathered claystone under the gravel reserve will not be disturbed. It will not have the
surcharge load removed. The ground water level will fluctuate in this azea but the pore water
pressure in the bedrock will remain relatively unchanged. These are all important factors in
determining the strength of a clay material.
3. It is impossible to perform a soils test (direct shear test) on an undisturbed sample of this
material. Simply by sampling the material the characteristics of the "in situ" claystone material
has been altered. A direct sheaz test can be performed on a remolded sample of the bedrock but
this test is not indicative of the strength associated with an undisturbed sample.
11990 Grant St. • Suite 304 • Denver, CO 80233 5441 Boeing Drive. • Suite 200 • Loveland, CO 80536-8855
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