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~ • iii iiiiiiiiiiiu iii <br />HEPWORTH-PAWLAK GEOTECHNICAL~INC. 5020 Road 1St 999 <br />Glenwood Springs, CO 81601 <br />• December 2, 1994 Fax 303945-8454 <br />Phone 303 945-7988 <br />NCIG Financial, Inc. <br />Attn: Peter Mattheis <br />0364 Storm King Road <br />New Castle, Colorado 81647 Job No. 194 548 <br />Subject: Comments Regazding Stability of Graded Cut and Fill Slopes, New Castle <br />Energy Mine Facilities, County Road 335, Gazfield Coun[y, Colorado. <br />Gentlemen: <br />As requested, we have reviewed the geotechnical reports and grading plan prepared for the <br />subject site and made a cursory review of the constructed grading conditions. The <br />purpose of our work was to develop opinions on the overall stability of the graded slopes. <br />Our review does not include the portal slopes. <br />Previous Studies: We were provided a geotechnical report prepared for grading design <br />and processing facilities by Chen & Associates (Chen, 1985). The grading plan was <br />prepared by Schmueser & Associates. A reproduction of the grading plan presented in <br />Chen's report is attached. <br />• Subsoil Conditions: TIIe subsoils encountered in the development azea by Chen's borings <br />consist mainly of gravelly sand and clay. Soils of higher gravel content and less clay were <br />also found. No free water was encountered to the drilled depths of 15 to 70 feet and the <br />natural moisture was relatively low. <br />Site Grading: We have not been provided an as-build grading plan. It appears from our <br />cursory observations of the site that the grading was generally conducted according to <br />Schmueser's grading design. The design cut and fill slopes range to a maximum height of <br />25 feet and maximum grade of 1 3/4:1 (horizontal to vertical) according [o the Chen <br />report. The on-site soils were used to construct the fill embankments. <br />Slope Stability: We did not observe indications of overall instability of the constructed <br />slopes. The soil conditions identified by Chen & Associates appear appropriate for the <br />stability analysis. Accordingly, we have assumed the following parameters: <br />Internal Friction: 32° <br />Cohesion: 200 psf <br />Moist Unit Weight: 125 pcf <br />Maximum Slope Height: 25 feet <br />Maximum Slope Grade: 30° (13/4:1) <br />Fully drained embankment and foundation <br />• We understand that graded slopes steeper than 2:1 require a safety factor of at least 1.3. <br />Based on the assigned subsoil and grading pazanleters, the calculated safety factor against <br />