PERMFILE114059

• Permit No: M2000144
• IBM Index Class Name: Permit File
• Section_Exhibit Name: ATTACHMENT A
• Media Type: D
• Archive: No

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ROCKY MOUNTAIN CONSULTANTS, INC.
Inc
Premiere Bulltling
825 Delaware Ave., Suite 500
Longmont, CO 80501
[phone]
Metro [phone]
FAX [phone]
(first Initial, lost name)@long.rmcco.com
February 10, 2001
Mr. Tom Schreiner
State of Colorado
Department of Natural Resources
Division of Minerals and Geology
1313 Sherman Street, Room 215
Denver, Colorado 80203
Re: Hall-Irwin Corporation North La Poudre Resource -Stability of the Sinclair Pipeline
File No. M-2000-144
Dear Mr. Schreiner:
Rocky Mountain Consultants, Inc. (RMC) was asked by Hall-Irwin Corporation to provide a design
for stabilization of the Sinclair pipeline lateral berm as requested by the Division of Minerals and
Geology (DMG) in a letter dated December 26, 2000 (Attachment A). The DMG letter specifically
required that a design be generated which would demonstrate and ensure equalization of
hydrostatic pressure between the two mining pods as it relates to the stability of the Sinclair
pipeline embankment.
RMC reviewed the Weld County FEMA Flood Maps and other available studies and determined
that the flow direction of the flood waters is generally from north to south in the project area,
immediately south of State Highway 392. Attachment B is a copy of the Weld County Flood
Insurance Map in the project area.
Two potential operational scenarios were evaluated for creating potentially erosive or destabilizing
conditions of the Sinclair pipeline. A description of each evaluated operational scenario,
conclusions drawn from the review of each scenario and design recommendations follow.
Scenario 1: West mining pod is full (or is not constructed) and the East pod is dewatered
Water flowing from north to south could spill from west to east into the empty east mining
pod eroding the toe of the mining slope and subsequently cause back-cutting of the
embankment.
RMC recommends that a soil embankment be constructed between the east and west pods
in a north-south orientation to prevent water from entering the east pod from the west. The
toe of this "erosion control embankment" should be constructed at least 10 feet west of the
proposed 3 horizontal to 1 vertical (slope stability Factor of Safety greater than 1.5) mining
excavation which parallels the Sinclair pipeline embankment. Refer Attachment C for
CIVIL AND ENVIRONMENTAL ENGINEERING PLANNING