2009-09-16_REVISION - C1980007 (3)

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BARR Barr Engineering Company 4700 West 77th Street • Minneapolis, MN 55435-4803 Phone: 952-832-2600 • Fax: 952-832-2601 • www.barr.com An EEO Employer Minneapolis, MN • Hibbing, MN • Duluth, MN • Ann Arbor, MI • Jefferson City, MO Memorandum To: Chris Nyikos From: Philip B. Solseng Subject: Stability Analysis Results Date: 16 September 2009 Project: Pond MBSE Evaluation c: Jed Greenwood, Brad Lindsay This memorandum presents the evaluation of stability performed by Barr Engineering Company (Barr) for the proposed Pond MBSE. The stability analysis addresses the requirements of the CDRMS. INTRODUCTION Pond MBSE is a proposed sediment control pond located on a terrace along the south bank of the North Fork Gunnison River, and below the existing screening plant at West Elk Mine. The pond will consist of two independently operated ponds that will allow one pond to be cleaned while the other pond is in operation. As part of the design, prior to construction of these ponds, Mountain Coal Company (MCC) is evaluating the stability of the ponds based on information from drawings by Roberts & Schaefer Company. As part of the evaluation, the proposed design of the Pond MBSE was reviewed, as well as data from a field investigation that included test pits to examine the existing conditions and a limited laboratory testing program to evaluate the physical characteristics of the existing soils. This information is summarized in Table 1. PROPOSED DESIGN The proposed design of Pond MBSE is shown on drawings CPP-COOS, CPP-0006 and CPP-0007 by Roberts & Schaefer Company. Relevant basic design information from these drawings is as follows: 1. Bottom of Pond Elevation (both ponds): 6039.5 2. Sediment Storage (each pond): 3. Detention Storage Elevation/Storage (both ponds): 1.5 acre-feet 6041.0/11.02 acre-feet