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<br />CONCLUSIONS <br />Based on the subsurface information obtained during this supplemental geotechnical <br />evaluation, the proposed configuration of the Refuse Disposal Area (RDA) and the <br />current construction practices, it appears that the completed slopes for the refuse <br />disposal area will have a minimum overall factor of safety against failure ranging from <br />l.6 to 1.7. <br />Based on the results of the laboratory investigation, it appeazs that the shear strength <br />values of the compacted, processed waste coal materials encountered a[ the si[e will be <br />equal [o or grea[er than the lower case value assumed and used in the original design <br />report prepared by CTL/Thompson. However, it appears that a ponion of the <br />processed waste coal materials being placed in [he RDA are not free draining, as was <br />assumed in the original report. The laboratory test results indicate that the majority of <br />the waste coal materials being placed in the RDA are cohesive and relatively <br />• impermeable in a compacted state. Therefore, the construction sequencing of the RDA <br />will have [o be modified to ensure [hat the processed waste coal materials aze properly <br />drained and dried ou[ prior to placemen[ and compac[ion. <br />A discussion of the geotechnical considerations rela[ed to the stability and construction <br />of the RDA are outlined herein. <br />PURPOSE AND SCOPE OF STUDY <br />This report presents the results of a supplemental geo[echnical investigation and stability analyses for the <br />Refuse Disposal Area (RDA) under construction within the Foide] Creek Mine in Routt County, <br />Colorado. 'T'his repon has been prepared to supplement the Geo[echttical Investigation prepared by <br />CTL/Thompson, Inc. which was prepared for dre RDA under their Job Number 22,253 and dated <br />January 17, 1995. <br />A field exploration program was conducted to ob[ain information on the portion of the RDA which has <br />been completed as of this date. Ma[erial samples obtained doting the subsurface investigation were [es[ed <br />• in the laboratory [o provide data on the classification and engineering chazacteris[ics of the processed <br />rob No. 97-3216 Northwest Colorado Consultants, inc. Page 1 <br />