_GENERAL DOCUMENTS - C1981017 (283)

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.0-- -33- 60th North Thompson Creek and Middle Thompson Creek exhibit similar baseline characteristics. Total dissolved solids content is low, generally between 100 and 300 mg/l . Suspended solids content is also low, except during snowmelt situations or thunderstorm events. The Fourmile Creek drainage also exhibits good water quality. Total dissolved solids concentrations average 150 mg/l , while total suspended solids concentrations normally fall below 100 mg/l. For comparisons of selected water quality characteristics,. please refer to Table 3. Probable Hydrologic Consequences - Surface Water The Coal Basin mine plan is designed to minimize the impacts on the surface water hydrology of the area. Mid-Continent has designed and constructed water control structures and closed water use systems to mitigate adverse impacts on the hydrologic balance. For more information on the drainage control plan, see Appendix II-8-7 in Volume 3 of the application and Section V of this document. The hydrologic consequences of mining in Coal Basin are expected to be minimal . The applicant' s statement of probable hydrologic consequences on page 22.1 of Chapter IV, Volume 7, predicted no affect on the quantity and quality of surface water other than increased sediment loading, but provided no supporting discussion. Therefore, the following is the Division's assessment based upon information contained in the permit application in Volumes 4, 5, and 7. The Coal Basin mine plan is designed to minimize impacts on the surface water hydrology of the region. Drainage from all disturbed areas is routed through one or more of 21 sedimentation ponds. Based on information presented by the applicant, there should be no effects on surface water quality from sediment pond discharge near the mines. Total dissolved solids, major ions, and metal contents are all similar to the receiving stream levels. However, discharge from the sediment ponds near the preparations plant will have an effect on water quality. Discharge from the sediment ponds at the preparations plant increases the soluble salt conten tw-an average of 8 mg/l . The metal content of the discharge and total suspended solids are lower than the receiving stream. This will not lower water quality. The release of sediment deficient waters into Coal Creek should not create any additional downcutting because of the rocky nature of the stream bed. Additional points where soluble salgs are added to the surface .eater system are the min t and seepage along Coal Creek from the refuse pile. The refuse pi e'seepage is the only additive source of metals at the mine site. The i on content of Coal Creek is increased by 0. 11 mg/1 which should 'nave an insignificant effect on water Quality. Seepage from the refuse pile a so incr=atpc `ha gn111ole salt r concentration oy an average of 4 ,ng/l which, is also insignificant.