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JD -8 Mine Drainage Design Plan — General Stormwater Comments <br />Page 2 <br />August 22, 2011 <br />2. Page 5, Section 2.2. Design Criteria. The third paragraph discusses design criteria for <br />riprap -lined channels. The reviewer could not find any peak flow analyses /calculations <br />or channel designs in Drainage Design Plan or the EPP. Please provide analyses and <br />designs to demonstrate the drainage ditches /channels have the capacity to pass the peak <br />flow resulting from the 100 -year, 24 -hour design storm. <br />3. Page 7, Section 2.4 and Table 6. There are some inconsistencies and errors in the table: <br />a. The stormwater pond area in the first paragraph (8,050 ft is inconsistent with the <br />pond area in Table 6 (8,047 ft DRMS acknowledges this is a rounding <br />difference, but requests consistent numbers be used. <br />b. The volume in cubic feet, in Table 6 is in error when compared to the volume in <br />acre -ft and gallons. It is also identical to the volume in Table 7. Please correct <br />the volume. <br />4. Page 7, Section 2.4. The last sentence of the first paragraph discusses passing the <br />remaining storm volume across the preexisting roadway through a culvert. The applicant <br />must: <br />a. show the location of the proposed culvert on Figure 2, and <br />b. Provide analyses and designs to demonstrate the proposed culvert has sufficient <br />capacity to pass the 100 -year peak flow. <br />5. Page 7, Section 2.4. The last sentence of the second paragraph suggests the applicant will <br />use silt fence to retain sediment should the pond not be able to be constructed as designed <br />and the pond overtops. In essence the applicant is intending to use silt fence to extend the <br />elevation of the retention pond crest. This is not acceptable. Silt fence is not intended to <br />be used as an embankment and will fail rather quickly if used for this purpose. The <br />applicant must commit to either increasing the area of the pond or building a higher <br />engineered embankment to provide the required storage. <br />6. Page 7, Section 2.4 (Routing Capacity). DRMS did not find any discussion related to <br />required spillway capacity or spillway design for the existing drainage conditions. Please <br />provide analyses and designs to demonstrate the retention pond spillways have the <br />capacity to pass the peak flow resulting from the 100 -year, 24 -hour design storm. <br />7. Page 9, Section 3.2 (Routing Capacity). DRMS did not find any discussion related to <br />required spillway capacity or spillway design for the operational and post- mining <br />drainage conditions. Please provide analyses and designs to demonstrate the retention <br />pond spillway has the capacity to pass the unattenuated peak flow resulting from the 100 - <br />year, 24 -hour design storm. <br />General Comment: <br />8. The applicant shall provide design specifications certified by a licensed professional <br />engineer for all Environmental Protection Facilities intended to convey, transport or <br />divert surface water and capture and /or retain surface water runoff from areas affected by <br />the Designated Mining Operation pursuant to Rules 6.4.21(10)(a)(ii) and (iii). <br />If either you or the applicants have any questions regarding the comments above, please call me <br />at (303) 866 -3567, extension 8169. <br />c:\documents and settings\grm\desktop\work folder \permits \cotter \jd -8, m -84 -014 epp \epp <br />review \stormwatercomments_mem22aug l l .docx <br />