REV00295

• Permit No: M2000087
• IBM Index Class Name: Revision
• Doc Date: 11/19/2001
• Doc Name: MEMO
• From: ROCKY MOUNTAIN CONSULTANTS INC
• To: ROCKY MOUNTAIN CONSULTANTS INC
• Type & Sequence: AM1
• Media Type: D
• Archive: No

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ROCKY MOUNTAIN CONSULTANTS, INC.
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MEMORANDUM
Inc
Premiere Building
825 Delaware Ave.. Suite 500
Longmont, CO 80501
3 3 172-5282
etro [phone]
FAX [phone]
(first initial, last name)@long.rmcco.com
TO: Danna Ortiz, Rocky Mountain Consultants, Inc.
FROM: Tim Cox, Rocky Mountain Consultants, Inc. ~~~
DATE: November 19, 2001
RE: Groundwater Analysis of Proposed Slurry Wall, Aggregate Industries Milliken
Site, Weld County, Colorado; R1vIC Job No. 80-3919.007.00
A groundwater analysis of the proposed slurry wall at the Milliken site was performed. The U.S.
Geological Survey's finite-difference computer program, MODFLOW (Groundwater Vistas version
2.5), was used to develop a demonstration model for the Milliken site. The model encompassed most
of Sections 7, 8 and l8 in Range 66 West, Township 4 North, covering approximately three and one-
halfsquare miles. The model was centered around the irrigation well (Permit No. 83028) on the
Kammerzell property. The Kammerzell property is immediately west of the ivtilliken site. The
irrigation well is 48 feet deep and was reported to yield 1,800 gpm in 1981 when the well was
reconditioned (personal communication, Mr. Kammerzell). The objective of the modeling was to
assess the impact of the proposed slurry wall on the imgation well.
MODEL SETUP
A two-dimensional model was constructed that simulated the alluvial aquifer within the South Platte
River valley (Figure I). The model consisted of 100-foot by 100-foot grid cells, 90 cells in the east-
west direction (columns) and l 10 in the north-south direction (rows). The underlying bedrock
formed the bottom of [he model. The model was bounded on the north by the Big Thompson River
and on the southeast by the South Platte River. The [,vo rivers were specified as constant head
boundaries and assigned elevations that approximated the slope (gradient] of the rivers. The east and
west boundaries were no flow.
The model simulated the saturated alluvium (sand and gravel) in the site vicinity. Bore holes drilled
on the Milliken site encountered alluvium to depths of 39 to 58 feet below ground surface, but the
bore holes did not penetrate the underlying bedrock. This suggests that bedrock may be greater than
58 feet deep in some areas of the Milliken site. The depth to bedrock on the Kammerzell property is
said to be from 35 to 66 feet (personal communication, Mr. Kammerzell). Therefore, [he saturated
alluvium in the model area could be as little as 3~ feet deep to 66 feet deep based on the available
data. The bottom of the mode] was assigned an elevation of zero and constant head elevations of the
two rivers were set so that the simulated water table would be approximately ~0 feet in elevation on
CIVIL AND ENVIRONMENTAL ENGINEERING PLANNING