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The alluvial aquifers of small tributarires within the Yampa River drainage <br />will be impacted both in terms of water quantity and water quality. Water <br />levels of the alluvial aquifers may be higher or lower than pre-mining levels <br />depending upon the proximity of mining to the aquifer and the relative <br />contribution of the spoils springs to the associated stream. Where mining is <br />conducted in close proximity to an alluvial body the water level in the <br />alluvial aquifer may be expected to decrease due to pumping within active <br />surface mine pits. This may occur near the Edna Mine on Trout Creek. <br />Development of spoils springs may increase the water level in the alluvial <br />aquifers through increased flow in the associated streams. The higher stream <br />elevation would result in a higher alluvial aquifer water level. Spoils <br />spring run-off from the Meadows No. 1 Mine is projected to have a negligible <br />impact on alluvial well levels along the Yampa River, due to the small <br />relative contribution of spoils discharges compared with flow in the Yampa. <br />Mining in Twentymile Park is not expected to alter the water quality in the <br />alluvial bodies along the tributaries of Trout Creek during or after mining. <br />The alluvial aquifers will be recharged by the streams during spring runoff <br />when stream salinity levels are low. Very little recharge to the aquifer is <br />expected to occur during baseflow periods when the stream is gaining water <br />from the alluvium. This interaction between the stream and the aquifer will <br />prevent the salinity of the alluvial aquifer from increasing above the <br />material damage limit. The expected water quality degradation would not limit <br />pre-mining water uses. <br />Mining in the Twentymile Park Basin will result in increased salinity and flow <br />in Trout Creek and its tributaries due to spoils springs and underground mine <br />discharges. In lower Middle Creek, stream flow and total dissolved solids <br />concentrations would increase primarily as the result of backfilled spoils <br />springs discharges and secondarily as a result of discharge from the Foidel <br />Creek underground mine workings. Irrigation water used along the lower <br />portions of Middle Creek is diverted from Trout Creek upstream of the reach <br />that would be affected by mining and, therefore, the quality of the irrigation <br />water would not be affected by mining. Water from Fish Creek is also used for <br />flood irrigation. The analysis indicates that the total dissolved solids <br />concentrations of Fish Creek would not exceed the use criteria for flood <br />irrigated waters of 2000 mgfl during the low flow months (August through <br />September) of dry years. The predictions were based on summations of <br />long-term discharges and of affected ground water from surface and underground <br />mining and surface flows. Ground water discharges to the stream/alluvial <br />aquifer system. Flow in the alluvial aquifer would help buffer the effects of <br />mining. Both surface and alluvial ground water would be degraded, but surface <br />flows would not be affected to the extent predicted by the worst-case <br />analysis. The water quality on Fish Creek would still be within acceptable <br />limits to support existing and potential water use. <br />Lower Trout Creek and the adjacent Yampa River are used for both flood <br />irrigation and domestic water. The projected impacts from mining would not <br />limit these uses, due to adequate dilution capacity. <br />The cumulative hydrologic assessment indicates that the proposed mining <br />operation has been designed to prevent material damage to the hydrologic <br />balance outside the permit area. <br />-10- <br />