2010-01-25_PERMIT FILE - C1981044A (3)

Home Browse Search

Ground water discharge from bedrock aquifers probably occur where the bedrock aquifers subcrop in the Yampa and Williams Fork Rivers. Groundwater from these aquifers flows into and recharges the alluvium. Due to the low permeabilities of the bedrock aquifers and the alluvium, this recharge is presumed small. Very few springs occur near the mine site, and their flows total less than 20 gpm. None of the springs appear to originate in any of the major bedrock aquifers. A spring survey was conducted by EC in 1982 and 1983. Detailed information concerning springs within the EC Permit area and [he spring survey are presented in Section 2,04.7, Hydrology Information. The direction of ground water flow in the alluvial aquifers is generally sup-parallel with the river valley or towards the river valley. Ground water discharge from [he alluvium to the river adds to the base flow in the rivers during the late summer, fall, and winter months. During the spring months, high flows in [he rivers recharge the alluvium. SURFACE WATER HYDROLOGY Surface water hydrology near [he EC Mine site is dominated by two rivers, the Yampa River and the Williams Fork River. The Yampa River is the major river and flows in a southwesterly direction across the pemtit area. Bear Creek, the headwater of the Yampa River, originates above Yampa, Colorado in the Sierra Madre Mountains. The Yampa River is characteristic of snowmelt streams with as much as 75 percent of the total annual discharge occurring during the months of April through June. Less than two (2) percent of the annual discharge occurs during [he fall and winter months, at which time the flow consists mostly of ground water discharge and base snowmelt. The second river of importance is the Williams Fork River. The Williams Fork River is a major tributary to the Yampa River and joins the Yampa River within the mine permit area. The headwaters of the Williams Fork River originate in the vicinity of Dunckley and Beaver Flattops. The Williams Fork River flows in a northerly direction through the mine permit area. The Williams Fork River like the Yampa River, is a snowmelt stream. Approximately 85 percent of its annual discharge occurs during the spring runoff. There is no major ground water reservoir that feeds the Williams Fork River. Therefore, sustained base flow during the fall and wiener months is very low. Intermittent tributaries to the Yampa and Williams Fork Rivers contribute to the total annual discharge. These tributaries are ungauged and there is no quantitative information available to predict their runoff. However, because these tributaries yield water only during infrequent periods of thunderstorm activity or during the spring snowmelt, their contribution is not considered significant. Most of the flow for both the Yampa and Williams Fork Rivers is derived from headwaters of basins where the winter snowpack is greatest. A generalized picture of the regional hydrology is presented on the Regional Hydrology and Geology Map (Map 11). WATER OUALTI'Y Surface water quality within the EC Permit area is suitable for most uses including irrigation, livestock watering, and industrial use. Suspended solids concentrations are normally low except during periods of high runoff caused by spring snowmelt or summer thunderstorms. Ground water quality in bedrock aquifers is suitable for most uses including potable supply, irrigation, livestock watering, and most industrial uses. Dissolved solids concentration in most instances meet recommended drinking water standards. Metal concentrations are usually less than maximum permissible limits for drinking water. The quality of ground water in alluvial sediments is generally poor. Dissolved solids and metals concentrations typically exceed maximum recommended and maximum permissible drinking water standards. Often ground water quality in alluvial sediments exceeds recommended standards for agricultural uses. The quality of water discharged from the No. 5 Mine is usually suitable, with limitations, for some uses including irrigation. The relatively high dissolved solids concentrations from these discharges usually render them unsuitable Permit Revision 04-34 2.04-4 Revised 7/2/04