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MEMO <br />Date: January 20, 2005 <br />From: Tom Kaldenbach <br />To: File <br />Permit number: <br />Doc. Class: <br />Doc. Type/Sequence: <br />Doc. Name: <br />C-1981-023 (Chimney Rock Mine) <br />Revision <br />MR-53 <br />Memo -Summary of Adequacy Review <br />I have completed my review of the above-referenced MR, and conclude it is ready for <br />approval upon receipt of a certified copy of Figure 1. The results of my review aze <br />summarized below. <br />Selection of Dso - The consultant sized riprap for channel lining using Figure 5.3 of the <br />Surface Mining Water Diversion Manual (OSM TR 82/2, 1982). This method applies to <br />channels on steep slopes. The 40% slope at Chimney Rock is at the limit of the curves <br />shown in Figure 5.3, necessitating extrapolation of the Dso value from the curves. The <br />extrapolation appears reasonable. As a check, I ran SEDCAD's ditch design utility using <br />the Simons/OSM method (see attachment). The run verified the consultant's selection of <br />DSO= 12". <br />Riprap size gradation -For steep channels the main concern with gradation is smooth <br />gradation to riprap sizes smaller than DSO in order to avoid large voids (page 5.5 of the <br />OSM Diversion Manual). Section A-A' of Figure I of the design indicates such a <br />gradation. <br />Riprap thickness -Section A-A' of Figure 1 of the design indicates riprap thickness <br />would achieve the thickness of 1.25 X DSO recommended for steep slopes on page 5.8 of <br />the OSM Diversion Manual. <br />Riprap angularity - The design appropriately specifies angular rock. <br />Need for filter layer - A filter layer is not needed based on the recommended filter layer <br />specifications of the Army Corps of Engineers and Bureau of Reclamation (page 5.2 of <br />the OSM Diversion Manual), as shown below. <br />