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stormwater discharge permit as is currently in affect is appropriate and sufficient for this operation. The operator will forward any coorespondence to DMG as soon as it is a~~ailable. 15. From your comments on page 2 of your adequacy review coorespondence dated 12-26-96, I assume that the design of the storm ditch from pond # 1 across the existing pit and stockpile area to the north end of the existing pit is acceptable to the Division. From that point non:hwards to sediment ponds 5, 6, and 7, a stormditch will be constructed with the following desil~r criteria: the ditch dimensions will minimally facilitate the maximum peak discharge anticipated, 200 cfs, in a trapezoid shaped with minimum 4 feet measured across the bottom of said ditch and 2:1 sloping sides with minimum depth of ditch 2 feet vertical. This will result in a ditch dimension of app. 12 feet wide as measured across the top of the ditch. Where the ditch is located in bed- rock, no geotextile liner will be used. In areas where soils or other unconsolidated material is encountered, Typar Class A Drainage Geotextile (CDOT specification) will be applied prior to rip-rap placement. The typar geotextile will be secured to the surface via 6" steel staples on 3 foot centers where possible and sides of the typar will be interlocked into the soil by trenching, stapling, and backfilling the edge of the geotextile in a 6" deep ditch running along the edge of the typar application. At intervals of 50 feet, the typar liner will be interlocked to the: substrate materials via a 1 foot deep by 1 foot wide trench cut perpendicular to the line (across) the ditch direction. The typar will be folded into the trench, stapled, and backfilled prior to continuing with the typar application in the ditch. The interlocking cross ditch trenching will al::o be used for all end of run and joining of separate typar sections. A graphic representation of a typical typar installation can be reviewed following page 6 in the permit application package which shows a typical spillway construction method, with the exception of the rip-rap placement. Rip-rap placement will follow current CDOT and Corp of Engineers design criteria fir placement and depth of rip-rap placement in drainage channels and storm ditches. Along the path the stormditch, rip-rap will be sized as follows: less than 2% grade, up to 1 foot rip-rap placed directly on a bed rock ditch or on typar liner at a minimum depth of 2 feet, at ;trades of 2- 4%, minimum 1 foot rip-rap up to 2 foot diameter rip-rap placed at a minimum depth of 4 feet on bedrock or properly installed geotextile, and in runs of ditch over 4% grade, minir, rum 2 foot rip-rap up to 3 foot rip-rap placed at a minimum depth of 6 feet over bedrock or geotextile. The exact location of the inlet of the first (upper) sediment pond will be based on placing the sediment ponds as low an elevation as possible within the affected land boundaries for the longest effective term of use given the slow but continuing lowering of final elevation within the pit. The mine operator will utilize the existing topographic features (natural drainage channels) as much as possible to connect the stormflow diversion with the series of sediment ponds. A constant grade from the north end of the existing pit area to the first sediment pond is not planned. Flatter stretches of ditch will be connected to steeper runs of ditch follovvin;; the general guidelines as explained above. With these parameters in mind, it is likely that most of the storm ditch path will be lined with 3 foot rip-rap minimally 6 feet deep. This siziag and depth of rip-rap is designed to stay in place and effectively handle stormflows up to 200 cfs and stream velocities in excess of 15 fps. 5