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TRAPPER DINING INC. <br />July 31, 1985 <br />CERTIFIED P176278353 <br />Mr. Gregg Squire F.11n 2 ~{I,yC <br />Reclamation Specialist <br />Colorado Mined Land Reclamation Division 1 ~ <br />423 Centennial Building , <br />1313 Sherman Street <br />Denver, Colorado 80203 <br />Dear Gregg: <br />The following Technical Revision to our permit (No. CO-010-81) is submitted to <br />revise the configuration of our Johnson Gulch series of sedimentation struc- <br />tures. This change to the previously submitted configuration (Johnson Gulch <br />Technical Revision, March 23, 1984) was necessitated by the probability that <br />• Johnson Dam 7k6 would not survive during the regrade of north Ashmore Pit spoils. <br />Also, the original location for Johnson Dam I)10 was moved 300 feet up-drainage <br />in order to avoid a 2" high-pressure gas line. The gas line was discovered dur- <br />ing topsoil stripping operations. <br />The new configuration (shown on the revised M51 series of maps) includes Johnson <br />Dams d/1 (enlarged), d)7, 4)7A, /)8 (enlarged), 4)9 and //10. The total drainage area <br />is 1,326 acres which will produce 15.5 acre-feet of runoff. Total disturbed <br />acreage through 1986 is approximately 560 acres requiring 11.2 acre-feet of sed- <br />iment storage capacity. Thus the total impoundment requirement is 26.7 acre- <br />feet. The proposed series of ponds has a design storage volume of 28.59 acre- <br />feet. <br />SEDIMOT II software was used to evaluate the new configuration fur both a <br />10-year, 24-hour event and a 25-year, 24-hour event. All assumptions used are <br />shown in Appendix A, SEDIMOT Output. Also shown on the printout are dam design <br />criteria and pond performance. The SEDIMOT Ii model predicts a peak settleable <br />solid (SS) concentration of .0269 ml/1 for a 10-year, 24-hour event at the John- <br />son Dam dF10 outflow. Under our NPDES permit, we are held to .5 ml/1 SS concen- <br />tration for storm water runoff. Map 1 shows the dissection of the drainage into <br />junctions, branches, and structures as used in the program. Tab Le 1 provides <br />key elevations for sediment pond design in Johnson Gulch. <br />Two bypass ditches have <br />our series of ponds. <br />• Gulch Bypass Ditch Nos. <br />revised Map M51, sheet <br />Contd. <br />been implemented to route undisturbed runoff away from <br />Appendix B shows the design of these ditches (Johnson <br />1 and 2). The location of the ditches is shown on the <br />2. <br />P.O. Box 187 Craig, Colorado 81626 (303) 824-4401 <br />