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2.04.7 Hydrology Description <br />Generally, seasonal variations in stream discharge shows peak rates in late <br />spring and early summer (April-July). Low flows begin in October and end in <br />March. Daily peak flows are typically around 12 midnight and low flows are <br />around 12 noon, due to snowmelt. <br />(b) (ii) (A through G) <br />Water quality data identifying seasonal variations are presented in this section <br />and Volume III, Exhibit 3. <br />Generally, seasonal variations in water quality are functions of flow rates. Total <br />suspended solids and flow peaks coincide due to the erosional nature of run-off <br />due to snow melt events. <br />Total dissolved solids and electro-conductivity diminish as functions of peak flows <br />due to the diluting effect of run-off events. The pH values or acidity of surface <br />waters usually remain stable during peak flows and either increase during low <br />flow due to increased concentrations of caliche derived soluble material, or <br />decrease due to higher concentrations of humic material, depending upon <br />vegetation influences on the drainage basin. <br /> <br />(3) Mining in the D-Seam could dewater saturated portions of the seam and may <br />temporarily dry the D-Seam outcrop and the related springs and seeps. After <br />mining, the eastern section of the mine should fill with water to approximate <br />premining levels. The water quality in the mine could be degraded because it will <br />be exposed to collapsed strata. The probable impact would be an increased <br />concentration of TDS, iron and manganese and possibly sulfate. Although no <br />data for permeability or transmissivity of the saturated portions of the coal bearing <br />member of the Mesaverde Formation are available within the permit area, the <br />experience by others (Brooks, 1983) suggests the Mesaverde Formation <br />transmits little water. Therefore, the coal mining operation is not expected to <br />result in the contamination, diminution, or interruption of an underground or <br />surface source of water. The surface drainage system in the surface facilities <br />area will not be interrupted. The mining operation could impact the surface <br />drainage system by increasing the sediment load in the streams. This impact <br />should not occur because run-off from disturbed areas will be passed through <br />sediment ponds or some other form of alternative sediment control. Mine water <br />discharge could impact the surface drainage system by mixing mine water with <br />surface water. Mine water is typically high in total dissolved solids (TDS) relative <br />to surface water so mixing mine water with surface water would be expected to <br />increase the TDS of the resultant mix. <br />Hubbard Creek and Terror Creek are located east and west of the projected mine <br />plan area. These creeks will be protected from the effects of subsidence. See <br />section 2.05.6. <br /> <br />PR-10 <br />1) PPRav~D <br />2.04 - 35 - 09/26/08 <br />