Laserfiche WebLink
On a smaller than regional scale, some impacts are expected. The sizes of drainage areas for some <br /> ephemeral and intermittent creeks within the mined area will be changed, thus altering runoff <br /> quantities. Other expected changes include: <br /> • Hydraulic transmissivities within backfilled pits will be altered, thus changing the <br /> hydrologic balance. <br /> • Base flow in creeks may be reduced during mining and for several years after mining. <br /> • Peak flows in creeks will be reduced due to pits. <br /> • Natural springs might experience increased or decreased flow or be completely <br /> eliminated. <br /> The Mine' s consumption of surface water will possibly affect the agricultural practices on a minor <br /> portion of the Good Spring Creek valley floor. However, since Colowyo owns the property to be <br /> withdrawn from irrigation and since these lands are not an integral part of any ranching or farming <br /> operation, the effect will be minimal. Exhibit 7 of the approved PAP discusses the water rights <br /> augmentation plan for the mine. <br /> Potential Effects on Surface Water Quality <br /> The 1982 Findings Document projected that no significant adverse impacts to surface water quality <br /> from mining operations will occur in or adjacent to the permit area. Subsequently, however, the <br /> Division has determined that some impacts are anticipated. Spoil spring development and increased <br /> salinity due to leaching in the backfilled pit areas is anticipated to be the most significant impact to <br /> the hydrologic balance in and adjacent to the mine area. Degraded spoil water will move down <br /> gradient through undisturbed strata and emanate as springs on the steep hillsides. This degraded <br /> water will mix with flow in receiving waters, including Good Spring Creek. Colowyo has provided a <br /> calculation of salinity increases in Good Spring Creek down gradient of the confluence of the West <br /> Fork of Good Spring Creek in Section 2.05.6(3)(b)(111) of Volume 12 of the PAP. Impacts to <br /> irrigated areas immediately downstream of monitoring site EFGSC are possible and are discussed in <br /> the alluvial valley floor section of this document. <br /> In the past, the Division has found that the operations at the Colowyo Mine have been designed to <br /> prevent material damage to the hydrologic balance outside the proposed permit area. The Division is <br /> in the process of analyzing recent data from water quality sampling of the Yampa River and <br /> tributaries potentially impacted by the Colowyo Mine. <br /> Three streams could potentially be affected by mining in the Collom area which include Little <br /> Collom Gulch, the West Fork of Jubb Creek and Collom Gulch. Evaluations of each stream was <br /> made for changes in direct surface runoff, changes in stream base flow amounts, changes in surface <br /> water interactions, effects from discharge of water from sediment ponds and effects from discharge of <br /> excess dewatering well flows. Potential effects on surface water quality for the Collom area is <br /> outlined in Volume 15, Section 2.05.6 in the PAP. <br /> 36 <br /> Permit Revision No.5(PR-05),C-1981-019 <br />