Laserfiche WebLink
<br />• <br />embankment fill volume. The ponds will detainrun-off. Emergency spillways and <br />pertorated riser pipe outlets are planned. <br />We recently reviewed operating conditions and stability for eight existing <br />pond embankments (Reference 9). For these ponds, the maximum water storage <br />height (difference in elevation between lower perforation of riser pipe outlet and <br />the interior toe of the embankment) was about 6 feet. The operating conditions for <br />the proposed ponds were not planned at this time. We assumed 10 feet maximum <br />height of water impoundment. <br />PREVIOUS INVESTIGATIONS <br />CTL ~ Thompson, Inc, has performed several previous geologiclgeotechnical <br />investigations at the site. Thesearelistedattheendofthisreport.Ourexperience <br />both from investigations and observations of spoil fill construction were considered <br />for this report. <br />GEOLOGIC CONDITIONS <br />Sedimentation ponds and embankments are planned in flatter portions of the <br />valley (Fig.1). Existing grades in the areas of the sedimentation ponds are about 5 <br />to 10 percent. <br />Bedrock at the site consists of interbedded sandstone, siltstone shale and <br />cgal of the Williams Fork Formation. Surticial soils consist of a thinner layer of <br />residual and colluvlal soils on steeperslopes,and deeper colluviallalluvial soils in <br />the valley bottoms. The colluviallalluvial soils typically consist ofgravel toboulder- <br />sized bedrockfregmentswithin aclayey sand matrix. The deposits can be stratified <br />with occasional sandy clay seams. No signs of mass instability were observed in the <br />area of the proposed sedimentation ponds. <br />NENNECOTT ENEROY <br />GOLOWYO COAL COMPANY -5011TH TpVLOR SEDIMENTATION POND <br />CTL~T JOB NO. 96,eb~ <br />z <br />• Each. 7-20F-6 Revision Date: 1/05/07 <br />Revision No.: PR-02 <br />