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, toner- E_ngineering & ,__jurve ing, <br />Date: lune 30, 2015 <br />To: Marcia L. Talvitie, P.E. <br />Environmental Protection Specialist II <br />DRMS-Durango Field Office <br />691 Co. Rd. 233, Suite A-2 <br />Durango, CO 81301 <br />From: Ryan Griglak, P.E. <br />Stoner Engineering & Surveying <br />Re: King Coal II — Preliminary "As -Built" Hydrology Analysis Permit C-1981-035 <br />Enclosed is the preliminary "as -built" hydrological analysis for GCC Energy, LLC's King II Mine <br />located at 6473 County Road 120, Hesperus, Colorado 81326. The analysis includes all the <br />drainage control structures located on the site. The computer modeling was done with SEDCAD <br />version 4.0. The information for the analysis was obtained from aerial topography <br />supplemented with a detailed field survey. <br />The aerial topography has a much greater degree of accuracy than what was available for the <br />original study. The basin size was slightly reduced and the soil properties modified to more <br />accurately reflect the actual site conditions included the original report. Please see the <br />enclosed information for the actual values. These changes resulted in an increase in the <br />amount of run-off the East and West Clear Water Ditches experience during the design event. <br />The increased flows do not exceed the capacity of either of the clear water ditches. <br />The minimum culvert installed on-site is a 16 -inch CMP due to maintenance considerations. <br />This results in the internal culverts being generally oversized from the results of the SEDCAD <br />modeling. The detention pond has the necessary volume available to store the 25 -year, 24- <br />hour storm event. <br />Please let me know if you have any questions or comments in regards to the information <br />provided. <br />Sincerely, <br />Ryan M. Griglak, P.E. <br />P.O. Box 1163 <br />970.565.7483 <br />28 South Washington Street <br />tcneren nee <br />_r« fronyet net <br />__. <br />Cortez, Colorado 81321 <br />970.565.7704 <br />_VIRI as <br />D c— c— 2—U VS <br />