PERMFILE53729

• Permit No: M2004022
• IBM Index Class Name: Permit File
• Doc Date: 5/13/2004
• Doc Name: Slope Stability Analysis and Proof of Notification
• From: Banks and Gesso LLC
• To: DMG
• Media Type: D
• Archive: No

ENGINEERING SOLUTIONS FROM THE GROUND DOWN
26 March 2004
File No. 103070-001
JCB Engineering, LLC
106 Rock Bridge Court
Windsor, Colorado 80550
Attention: John Vazquez
President
Subject: Slope Stability Analysis for Town of Windsor Water Pipeline
Raindance Sand and Grave] Mine
Windsor, Colorado
Mr. Vazquez
Lyman Henn, Ina (Lyman Henn) is pleased to present JCB Engineering, LLC (JCB) the results of a slope
stability evaluation of the proposed final excavation and reclamation slopes adjacent to the Town of Windsor
water pipeline at the proposed Raindance Sand and Gravel Mine (a.k.a. Whiting Farm Reservoir). The proposed
mining plan consists of an eastern and western pit separated by native soils which support the pipeline alignment
The pipeline alignment is north/south direction, as shown in Figure 1.
Lyman Henn performed these stability analyses using proposed slope configurations provided by JCB. Since the
geometry of the proposed slopes are nearly identical on both the east and west sides of the existing pipeline,
Lyman Henn performed an analysis of the proposed excavation configuration to the east side of the existing
pipeline, which was approximately 3 feet higher. We analyzed the two scenarios, 1) during mining, where the
excavation came closest to the pipeline, and 3) at final build out with an operating reservoir. The analyses were
performed using; 1) existing information from the site provided by JCB and Banks & Gesso, LLC, 2)
conservative assumptions for material strengths for the natural soil materials in the proposed cut slopes, 3) worst
case piezometric (groundwater) conditions for the slopes, and 4) Lyman Henn's understanding of the proposed
mining plan. Lyman Henn has prepared this letter report summarizing the results of the analyses. We also
recommend a meeting with yourself and Mr. Martin Lind to present our findings.
SITE CONDITIONS
Based on information provided in Teracon's preliminary sand and gravel mineral evaluation report for the
proposed gravel pit, Lyman Henn understands that the subsurface conditions in the vicinity of the pipeline consist
of topsoil, overburden, and sand and gravel overlying sedimentary bedrock. Top soil was encountered at the
surface and consisted of a 6 to 8 inch layer of silty cultivated soil. Overburden was encountered beneath the
topsoil and extended to depths of approximately 4 to 10 feet below ground surface. The overburden consisted of
cohesive clayey sand and sandy lean clay. N values ranged from 2 to 6.
110 16th Street, Suite 900 - Denver, CO 80202-5202 -Tel: [phone] -Fax: [phone] - www.LymanHenn.com
Geotechnical, Tunneling and Construction Services