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-24- result in an increase in dissolved calculations below). This impact total ground water quality in the any water quality criteria. solids of approximately 80 mg/l. (See is considered to be insignificant to the basin and will not result in exceedance of Dissooved Solid Concentration Unmined portions of the Vermejo Formation - 829 mg/1 Mined area within Twin Pines permit area - 1019 mg/1 Mined area within Dorchester permit area - 1660 mg/1 Concentration of TDS = .004 (1019)mg/1) + .03 (166Qng/1) + ,966 (829mg/1) = 909 mg/1 .0 Net increase in TDS = 909 mg/1 - 829 mg/1 = 80 mg/1 Impacts on Surface Waters The Division, based on review of the permit applications for the mining operations considered in this assessment, has identified several possible effects of mining on surface water quality and quantity in the Canon City Coal Field. Surface water quality may be effected by: 1) Erosion and subsequent increased sediment loads to streams; 2) Discharge of mine water to receiving streams; 3) Seepage water through waste rock or coal a refuse material; or 4) Depletion of stream flow via subsidence-induced infiltrations. 1) Surface flow from disturbed areas from the one proposed and three permitted coal operations would carry higher sediment concentrations than natural runoff. However, Rule 4.05.2 requires that all disturbed flow pass through a properly designed sediment control pond. Effluent from the pond is required to meet NPDES limitations prior to discharge. During operation, monitoring and inspection by the Division ensures that the sediment control system is maintained to function as designed. At the close of operations, surface disturbances would be reclaimed and the sediment control system would be removed following the ensuing liability period. As a result, the increased sediment load carried by disturbed flows would not be expected to reach receiving streams. Furthermore, discharge points for each of the four mines are into ephemeral drainages which are characterized by very high sediment loads in their natural states. 2) Only one mine, the Dorchester No. 1 Mine, has proposed to discharge mine water into a receiving stream. The mine water will pass through a treatment facility prior to discharge. The company has stated, in Section 2.05.6(3) of their Second Adequacy Response, that the quality of the discharges will comply with effluent limitations. Quantitative assessments of the impact of this potential discharge have not been made. (See the Probable Hydrologic Impact of the Dorchester Mine for a further discussion.)