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Craig Ranch Pit — General Stormwater Comments <br />Page 4 <br />June 23, 2011 <br />a. The Applicant shall provide separate calculations for each proposed sediment <br />pond. Alternatively, the Applicant may provide calculations demonstrating that <br />one or two sediment ponds are adequate to store the design storm runoff volume if <br />it is also demonstrated that collection ditches are sized adequately to convey <br />unattenuated peak flows from all areas ignoring sediment ponds for which no size <br />calculations are provided. Calculations shall address both operating and post - <br />reclamation conditions. <br />b. The Applicant shall provide a map delineating contributing areas for each <br />proposed sediment pond. <br />8. Page I -1, Soils Information — The third listed primary soil appears to be mislabeled as <br />"137 ". According to the Soil Survey Report — Engineering Tables that follow page I -1, <br />the number should be "45 ". Note: including the Hydrologic Soil Group (HSG) tables <br />would be helpful in supporting CN selection. <br />9. Page M -1, Other Permits — Item 2 states a process water discharge permit will not be <br />needed. However, a stormwater discharge permit will be required. <br />10. Pursuant to Rule 6.3.3(g), hydrologic analyses should include: <br />a. Maps delineating contributing areas, <br />b. Methodology summary (e.g., TR -55 using upland method for times of <br />concentration), and <br />c. Runoff transformation methodology, assumptions (e.g., SCS curve numbers, <br />including rationale and areas for each value selected, and calculations for times of <br />concentration for peak flows), and computations or model results. <br />11. Pursuant to Rule 6.3.3(g), hydraulic analyses should include: <br />a. Peak flow from the hydrologic analyses, <br />b. Channel shape including depth with freeboard (1.0 feet recommended), side <br />slopes, and bottom widths (if applicable), <br />c. Maximum and/or minimum longitudinal slopes, <br />d. Manning's roughness assumptions for channels (roughness values for both <br />capacity — i.e., highest expected Manning's n; and stability — i.e., lowest expected <br />Manning's n should be considered), <br />e. Estimated maximum flow depth in the channel using the capacity Manning's n, <br />f. Estimated peak flow velocity using the stability Manning's n (note: flow <br />velocities exceeding 5 feet per second will require revetment protection such as <br />riprap — sized appropriately), <br />g. Sediment pond spillway sizing (typically performed using weir equations), and <br />h. If any Culverts are planned, include sizing calculations or nomographs. <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 />m:\min \tc1 \m- 1986 -002 craig ranch\ stormwatercomments _mem21jun11.docx <br />