1988-04-11_PERMIT FILE - C1981008A (14)

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COLORADO DEPARTMENT of HEALTH Water Quality Control Dlvlsion 42.10 Last llth Avenue Denver, Colorado 110220 RATIONALE AMENDMENT NO. 1 PEA13ODY COAL - NUCI.A COAL MINE PERMIT NUMBER CO-0000213 MONTROSE COUNTY By letter of April 10, 1987, , the permittee has informed us of a new source of wastewater being discharged through outfall 001. Spoils spring water has begun emanating and Peabody has routed it into the 001 pond. The permit was written with Federal BAT limitations to cover discharges of surface runoff only. This new source necessitates a reassessment to determine whether additional limitations are needed to cover this mostly continuous source. For continuous sources, State water quality standards (WQS) must be met. The division uses a mass balance formula to calculate limits, then compares the limits to monitoring data to determine whether the limits must be imposed in the permit. The calculations for several parameters for this outfall are shown in Appendix A. The stream segment (Segment 12) which includes Tuttle Draw (immediate receiving water for outfall 001) has no metals standards. For this reason the division looks at maintaining the standards in the next segment (Segment 5, San Miguel River Subbasin, Gunnison River Basin). The 7-day, 10-year low flow for the San Miguel River at confluence with Tuttle Draw (7.0 cfs) is used. This looks at a worst case situation, that being where the entire flow in Tuttle Draw emirates from outfall 001 and the flow in the San Miguel River is at the Q7-10• Tile effluent flow which is used is the highest reported flow on file. The permittee submitted monitoring results from seventeen samples of the spoils spring prior to mixing with any waters in the pond 001. This data is used by the division for comparison. It is expected that effluent concentrations will be less than or equal to this data, due to settling which occurs in the pond. 7-6-33