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• <br />Item 36 <br />0 <br />The results of our observations and/or investigation at each sedimentation <br />pond location were favorable. The pond embankments are small (10 feet or less <br />height). In our opinion, this investigation (Job No. 32,611) and our previous <br />investigation of embankment sites (Job No. 26,559) provides sufficient observation <br />and investigation of the pond sites to confirm stability. <br />Item 37 <br />Our stability analysis of sedimentation embankments (Job No. 26,559) <br />indicated factors of safety of in excess of 2.4 for clayey foundation soils. We have <br />analyzed the minor changes requested (H=10', crest width = 12' and water height = <br />7.5') as shown on Figs.1 through 4 attached. Factors of safety in excess of 2,3 were <br />calculated for clay foundation soils; in excess of 1.5 for sand. <br />Based on our investigations, sand foundation soils will be found nearer the <br />center of larger valleys (i.e. in Lorencito Valley). Clay or clayey sand soils are <br />expected in remaining areas. Our analysis shows a 10 percent slope below the <br />embankment. The clay foundation soils maintain adequate stability with a 20% base <br />grade. Clean sand foundation soils result in factors of safety less than 1.3 with the <br />base slope at 20 percent. Where clean sand soils are found, grades are naturally <br />flatter since the clean, sorted material is not found on steeper slopes. Therefore, we <br />believe stability concerns are reduced. <br />We did not measure slopes at each exact pond location. If the base slope <br />exceeds 10 percent with sand foundation soils, revisions will be required. Based on <br />our observations, this condition is very unlikely. If the base slope exceeds 20 <br />percent with clay soils, stability should be checked. Since ponds are desired in <br />flatter areas to maximize volume, we do not expect this condition will occur. <br />We hope this provides the information you require. Please call if you have any <br />questions. <br />Very truly <br />Mark rj: Gray, P.E. <br />Project Manager <br />MGG/lr <br />(5 copies sent) <br />~. <br />~. <br />~~bi14~ y <br />r <br />'r ( ' ~h~ <br />~~~ o ,~'~ <br />• LORENCI70 COAL COMPANY, LLC <br />tlo GREYSTONE <br />CTLlT JOB NO. J2,811 <br />