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A. The site bench sedimentation pond collects run-off from <br />the highwall fill slope, the bulk of the mine site, the ramp <br />to the North Spoil Area, and eventually the North Spoil <br />Area. Mine water discharge is also pumped into the pond. <br />Settled water from the pond is discharged through a 10" pipe <br />into Lewis Gulch. An energy dissipating structure has been <br />provided at the outlet in Lewis Gulch. Fill slopes have now <br />obtained a good cover of vegetation thus reducing sediment <br />load in the ponds. <br />B. The lower sediment pond collects run-off from the ramp to <br />the upper bench, the southern elevated portion of site <br />bench, the fill slopes and access road below the site bench, <br />and the truck loading and stockpile area at Lewis Gulch. The <br />lower pond discharges directly into Lewis Gulch. <br />During major storm events experienced at the mine site a portion <br />of the run-off from the slopes above the upper bench will flow <br />into the Bench Sedimentation Pond. <br />Top soil stockpile areas adjacent to the Mine Access Road have <br />produced substantial vegetation and have been provided with a <br />berm to contain run-off from the piles. <br />Details of the ponds and initial calculations are shown on Sketch <br />nos. TPS-1 & TPS-2. Drainage plans and the location of berms, <br />ponds etc. are shown on the "Mine Site Plan", drawing no. TP-3. <br />• The ponds have met performance standards during the first 7 years <br />of operation of the mine. They have been subjected to storm <br />events which in all probability exceeded the design event with <br />satisfactory performance. Discharge from the ponds is monitored <br />in accordance with the NPEDS permit issued by the Colorado <br />Department of Health. No violations for standards set forth in <br />the permit have been received. <br />Twin Pines does commit to maintaining the sediment level in the <br />ponds in accordance with the Regulations. <br />Run-off from the mine yard is collected in a drainage swale which <br />runs in front of the Mine entries and terminates in the 24" CMP <br />intake to the bench pond. The swale was designed to contain the <br />run-off from the mine yard and protect the underground entries <br />from the intrusion of storm water. The swale varies in section <br />and will carry normal run-off from a 25 year storm event. <br />Also included in the mine plan is a fill across Lewis Gulch which <br />serves as a truck loading and coal stockpile area. To accommodate <br />flood flows in the dry gulch, a 60" CMP was chosen to handle a <br />100 year 24-hour flood. Incorporated with the fill is the lower <br />sedimentation pond. The facility does provide detention for flood <br />flows in Lewis Gulch. The embankment is classified as a roadway <br />fill and therefore does not fall under the jurisdiction of the <br />State Engineer. Design calculations of the culvert are included <br />in Appendix A. <br />~C <br />Ph'GE1~ REVISED ~ra~ •~' ` .; '~~. <br />ii/30/4 ~ , ~- <br />