Laserfiche WebLink
Basin). In contrast, the maximum reported sulfate concentrations at the lower Yampa River monitoring site was <br /> 180 mg/1. <br /> III In cases where ambient concentrations were found to exceed applicable stream standards, mine impact analyses <br /> by the WATBALP prediction module or any other analysis would be expected to indicate such exceedances of <br /> stream standards. <br /> In summary, in an analysis separate from the modeling, ambient water - quality concentrations were assessed <br /> relative to those variables (primarily trace metals) considered in applicable stream standards promulgated by the <br /> State of Colorado. These involve Segments 13a, 13b and 13c (Trout Creek and tributaries outside of Routt <br /> National Forest) and Segment 2 (mainstream Yampa River). Primary emphasis was placed on comparing data <br /> for 15 monitoring sites in the Trout Creek Basin. Ambient conditions based upon historical data prior to the <br /> proposed expanded mining exceeded stream standards set by the Colorado Department of Health for the <br /> following water - quality parameters: sulfate, boron, cadmium, lead, mercury, zinc, total iron, and total <br /> manganese. Several of the excessively high concentrations occurred in headwater tributary reaches upstream <br /> from any current mining activity. In addition, a basinwide survey of water quality conditions for the Yampa <br /> River Basin revealed ambient conditions exceeding stream standards (Wentz and Steele, 1980). <br /> In the case of several trace metals (cadmium, lead, and perhaps mercury), the noted average or extreme <br /> concentrations may involve minimum analytical detection limits which are greater than the standard limits. At <br /> any rate, a critical assessment of currently applicable standards, and the extent to which they should be shifted <br /> downward to reflect more realistically ambient conditions, should be conducted before conducting a post mining <br /> mine impact analysis. <br /> No recent (since 1997) exceedances of discharge limits of pH were recorded at the mine. In addition no <br /> exceedances of the manganese or iron in- stream standards attributable to the mining operations have been <br /> 0 observed (Annual Hydrologic Reports). <br /> (Note: The previous calculations and analysis were based on the premise that EC and sulfate standards <br /> were applicable for Lower Trout Creek, based on the stream designation for water supply. Subsequent <br /> review by the WQCD determined that these standards are not applicable if there is no active water <br /> supply useage. So the following information is no longer valid) Exhibit 51, Tables E51 -12 to E51 -14 present <br /> predicted in- stream TDS, conductivity and sulfate values for Cases 1, 2 and 3 for normal and dry years. The <br /> tables indicate that the mine should be able to meet the conductivity limit of 1,500 µmhos /cm under most <br /> conditions, but will not be able to discharge at maximum rates during low flow conditions due to the inability to <br /> meet the sulfate standard (250 mg/L). Exhibit 51 Tables E51 -15 presents the maximum discharge rates from <br /> Sites 109 and 115 that will not cause an exceedance of the sulfate standard during a normal year. It indicates <br /> that in the future, Site 115 should be able to be discharged at higher rates than at present. Table Exhibit 51, <br /> Tables E51 -16 and E51 -17 present the in- stream flow rates required to not exceed the sulfate standard using dry <br /> year water quality data and maximum discharge rates from Sites 109 and 115. These tables also indicate that <br /> Site 115 may be able to discharge at higher rates in the future. Exhibit 51, Table E51 -18 shows the minimum <br /> in- stream flow rate required in order to meet the sulfate standard using low flow water quality data and the <br /> minimum discharge rates from Sites 109 and 115 required to dewater all inflow. This table indicates that the <br /> mine can discharge at these rates under most conditions. <br /> Discharge of Ephemeral Runoff From Disturbed Areas <br /> Runoff from surface areas disturbed during construction of roads and facilities or by activities during operation <br /> and reclamation would be expected to be higher in suspended solids. The potential problem of increased levels <br /> of suspended solids in the surface runoff will effectively be mitigated during operations by construction and <br /> 0 operation of sedimentation control structures. The sedimentation control structures will be operated to effect <br /> compliance with the effluent limitations of the NPDES permit. Under the stringent limitations of the NPDES <br /> permit, the suspended solid concentrations of the discharge will be lower than the streams during the spring run- <br /> off period. Successful completion of reclamation activities as described under Rule 2.05.4 will provide effective <br /> surface erosion control and will result in runoff characteristics similar to the premining conditions. <br /> PRO9 -08 2.05 -158 04/27/09 <br />