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' `~ <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />t <br />1 <br /> <br /> <br />1 <br />1 <br />1 <br />-, <br />F ~ X ~ Consulting Engineers and Geologists <br />F.M. FOX 8 ASSOCIATES, INC. <br />47651NDEPENDENCE STREET <br />WHEAT RIDGE, COLORADO 80033 <br />(303) 424-5578 - FMFOX <br />Grand Mesa Coal Company December 31, 1979 <br />P.(), Box 2?6 <br />Delta, Colorado 81416 Job ;lo. 1-1364-4448-O1M <br />Subject: Revised Design and Construction Criteria for Rentention Dams at the Red <br />Canyon Mine Site Near Cedar Edge, Delta County, Colorado <br />Reference: Our Subsoil Investigation, Job N'o. 1-1364-4448-OOM, Dated December 3, 1979 <br />Gentlemen: <br />It is our understanding that only Dam Flo. 1 •,vill be constructed and will have a one <br />year life span. We have revised our design and construction criteria for this dam <br />based on the above and on the assumptions that the maximum pool depth of 10 feet trill <br />he utilized and that the foundation soils exhibit generally uniform permeability char- <br />acteristics. The compacted embankment soils and bedrock are assumed to be impervious <br />relative to the found aticn soils. <br />Based on the above, the follovring revisions can be ma:ie. The cutoff trench and relief <br />wells may be eliminated. In order to protect the dov+nstream toe of the dam from seep- <br />age uplift forces, a toe drain should be constructed as shown on Figure 1, attached. <br />In lieu of constructing the cutoff trench, the dcn embankment may be constructed on <br />properly prepared foundation soils. All ex ist.ing coal slag and sands encountered <br />at or near the around surface should be removed and vrasted from the site. The top <br />1 foot of the underlaying clay should be sca;°ified and recompacted to a minimum of <br />95Y of F4odified Froctor density (ASTM D-1557-70). Other items discussed under "Con- <br />clusions and Recommendations" and "Construction Recommendations" in the referenced <br />report concerning design and construction recommendations should be carefully fol- <br />lowed. <br />Ore are available to discuss the details of this report with you. W'e should be called <br />during construction to supervise and control the placement of fill and to inspect <br />the foundation soils prior to fill placement. If plans arc modified in the future, <br />r+e should be called to review arld revise our rr.cenlmendations and construction details <br />as necessary. Please call when further consultation or inspections are required. <br />F.M. FOX i; ASSOCIATES, INC. <br />w~^ - <br />David W. Potter <br />Staff Engineer <br />DWP/pcs <br />' Copies: 10 <br />1 <br />*~$~4395w~ <br />:4~ > . <br />ilk ~ ~ dV:,~ 0 <br />.~rf;~~ xCOyoq~ <br />ALBUOUEROUE • DENVER • PHOENIX <br />Revi ed by: <br />9t.. • , ~' <br />Donald R. f, ark, P.E. <br />Division Manager <br />